A Practical Guide to Polymeric Compatibilizers for Polymer Blends,
Composites and Laminates.
Jozef Bicerano, Ph.D.
Introduction
Fundamental Considerations
Overveiw of Available Compatibilization Technologies
Representative Examples of Vendors and their Technologies
Technology Outlook
Introduction
The development of polymer blends, composites and laminates is a very active area of
science and technology; of great economic importance not only for the plastics industry but
also for many other industries where the use of such products is becoming increasingly more
common.
Most pairs of polymers are immiscible with each other. Even worse is the fact that they also
have less compatibility than would be required in order to obtain the desired level of properties
and performance from their blends. Compatibilizers are often used as additives to improve the
compatibility of immiscible polymers and thus improve the morphology and resulting properties
of the blend. Similarly, it is often challenging to disperse fillers effectively in the matrix polymer
of a composite, or to adhere layers of polymers to each other or to other substrates (such as
glass or metals) in laminates. Continued progress in the development of compatibilization
technologies is, hence, crucial in enabling the polymer industry to reap the full benefits of such
approaches to obtaining materials with optimum performance and cost characteristics.
Term
Additive
Definition
Substance added to a polymer.
Holding together of two bodies by interfacial forces or mechanical
Adhesion
interlocking on a scale of micrometers or less.
Adhesion promoter
See Coupling agent.
Adhesion in which two bodies are held together at an interface by ionic
Chemical adhesion
or covalent bonding between molecules on either side of the interface.
Capability of the individual component substances in either an
Compatibility
immiscible polymer blend or a polymer composite to exhibit interfacial
adhesion.
Process of modification of the interfacial properties in an immiscible
polymer blend that results in formation of the interphases and
Compatibilization
stabilization of the morphology, leading to the creation of a polymer
alloy.
Polymer or copolymer that, when added to an immiscible polymer
Compatibilizer
blend, modifies its interfacial character and stabilizes its morphology.
Immiscible polymer blend that exhibits macroscopically uniform
Compatible polymer blend
physical properties throughout its whole volume.
Multicomponent material comprising multiple different (nongaseous)
Composite
phase domains in which at least one type of phase domain is a
continuous phase.
Topological condition, in a phase-separated, two-component mixture, in
Co-continuous phase
which a continuous path through either phase domain may be drawn to
domains
all phase domain boundaries without crossing any phase domain
boundary
Phase domain consisting of a single phase in a heterogeneous mixture
Continuous phase domain through which a continuous path to all phase domain boundaries may
be drawn without crossing a phase domain boundary.
Interfacial agent comprised of molecules possessing two or more
Coupling agent
functional groups, each of which exhibits preferential interactions with
the various types of phase domains in a composite.
Measure of the strength of the interfacial bonding between the
Degree of compatibility
component substances of a composite or immiscible polymer blend.
Discontinuous or discrete Phase domain in a phase-separated mixture that is surrounded by a
or dispersed phase
continuous phase but isolated from all other similar phase domains
domain
within the mixture.
Substance, especially a diluent or modifier, added to a polymer to
Extender
increase its volume without substantially altering the desirable
properties of the polymer.
Filler
Solid extender.
Phase domain of microscopic or smaller size, usually in a block, graft,
Hard segment phase
or segmented copolymer, comprising essentially those segments of the
domain
polymer that are rigid and capable of forming strong intermolecular
interactions.
Immiscibility
Inability of a mixture to form a single phase.
Immiscible polymer blend Polymer blend that exhibits immiscibility.
Adhesion in which interfaces between phases or components are
Interfacial adhesion
maintained by intermolecular forces, chain entanglements, or both,
across the interfaces.
Bonding in which the surfaces of two bodies in contact with one another
Interfacial bonding
are held together by intermolecular forces.
Region between phase domains in an immiscible polymer blend in
Interfacial region
which a gradient in composition exists.
Laminate
Material consisting of more than one layer, the layers being distinct in
composition, composition profile, or anisotropy of properties.
Matrix phase domain
See Continuous phase domain.
Capability of a mixture to form a single phase over certain ranges of
Miscibility
temperature, pressure and composition.
Miscible polymer blend
Polymer blend that exhibits miscibility.
Shape, optical appearance, or form of phase domains in substances,
Morphology
such as high polymers, polymer blends, composites and crystals.
Multiphase copolymer
Copolymer comprising phase-separated domains.
Composite in which at least one of the phases has at least one
Nanocomposite
dimension of the order of nanometers.
Region of a material that is uniform in chemical composition and
Phase domain
physical state.
Polymeric material, exhibiting macroscopically uniform physical
properties throughout its whole volume, that comprises a compatible
Polymer allloy
polymer blend, a miscible polymer blend, or a multiphase copolymer.
Macroscopically homogeneous mixture of two or more different species
Polymer blend
of polymer.
Composite in which at least one component is a polymer.
Polymer composite
Phase domain of microscopic or smaller size, usually in a block, graft,
Soft segment phase
or segmented copolymer, comprising essentially those segments of the
domain
polymer that have glass transition temperatures lower than the
temperature of use.
Melt-processable polymer blend or copolymer in which a continuous
elastomeric phase domain is reinforced by dispersed hard (glassy or
Thermoplastic elastomer
crystalline) phase domains that act as junction points over a limited
range of temperature.
Table 1: IUPAC-recommended definitions1 of key terms.
Before proceeding any further, it is important to summarize the definitions of some key terms,
as recommended by the International Union of Pure and Applied Chemistry (IUPAC), in order
to avoid any confusion. These IUPAC definitions are listed in Table 1.
This report provides a practical guide to the science and technology of polymeric
compatibilizers for polymer blends, composites and laminates. This definition of its scope has
several important implications:

The report does not include any quantitative information regarding current or projected
market sizes and market segmentation by product type and geographical region.

The focus of the report is on additives that are used as compatibilizers, rather than
being on polymer blends, composites, or laminates themselves. Consequently, while
many blends, composites and laminates are discussed as examples of the optimum
selection, use and effects of compatibilizers, we do not catalog and review the vast
range of existing and developmental polymer blends, composites, laminates and their
applications. It suffices to state that automotive and electrical/electronic applications
provide the broadest range of opportunities for new compatibilizers. Significant
opportunities also exist in the packaging, major appliance, sports/recreation
equipment and medical device industries; as well as in the continued development of
plastics recycling technologies.

Since our focus is mainly on "polymeric compatibilizers" (additives that are polymers)
used in blends, composites and laminates, many types of compatibilization additives
(surfactants, most liquid or powder additives of low molecular weight, silane and
titanate coupling agents; and silane, phenolic, titanate and zirconate adhesion
promoters) are not discussed.

Our focus is on providing a "practical guide" consisting entirely of information that
specialty chemical and polymer producers and compounders can use. Consequently,
a lengthy review of the vast and rapidly growing academic literature on
compatibilization is avoided. We also avoid a lengthy review of the rapidly growing
patent literature, much of which consists of patents on technologies which (while they
may have significant merit) will never become commercially significant. The author
believes that these deliberate omissions are essential in order to help focus the
reader's attention on the information that will be most useful in practice by avoiding
lengthy digressions from the practical focus.
Section 2 presents the "practical fundamentals" of compatibilization. The five key factors that
every compatibilization additive developer must consider in order to improve the likelihood of
achieving technical and commercial success simultaneously are identified and discussed.
These five factors are (1) performance versus price, (2) the thermodynamic equilibrium phase
diagram, (3) metastable morphologies often induced by processing conditions, (4) practical
implications of kinetic barriers to equilibration and (5) morphology-property-connections.
Section 3 provides a brief overview of the commercially available polymeric compatibilizers.
The largest number of compatibilizers, by far, are modified polyolefins, most of which contain
polar groups enhancing the compatibility of polyolefins with polar polymers, their ability to
couple with (and thus disperse) inorganic fillers more effectively, and their ability to adhere to
substrates. Some modified polyolefins contain reactive groups that may further enhance their
effectiveness. Styrenic block copolymers constitute the second largest class of
compatibilizers. These thermoplastic elastomers have hard blocks that segregate into a glassy
glassy hard phase and soft blocks that segregate into a rubbery soft phase. Other polymeric
compatibilizers include methacrylate-based polymers, polycaprolactone polyesters,
polycaprolactone polyester / poly(tetramethylene glycol) block polyols,
methacrylate-terminated reactive polystyrene, and mixtures of aliphatic resins of low or
medium molecular weight.
Section 4 discusses selected products of specific vendors as representative examples. The
multiple roles that the same additive can perform (especially blend compatibilizer, filler
coupling agent, adhesion promoter and impact modifier) are highlighted with many
examples
Section 5 provides an outlook on compatibilization technologies.
Fundamental Considerations
Performance Versus Price
As an empirical rule2 shown in Equation 1, if a polymeric product remains a commodity
material competing for use in commodity-type applications, the price that the average
customer is willing to pay will only increase proportionally to the logarithm of the improvement
in its performance:
In this equation, Price2>Price1, Performance2>Performance1 are the corresponding
performance levels, "c" is a positive proportionality constant and "ln" is the natural logarithm.
See Figure 1 for a schematic illustration. This equation can be generalized readily to more
complex cases where the overall "desirability" for a particular application depends on several
performance criteria that have different levels of relative importance.
Figure 1: Schematic illustration of the "commodity trap";
namely, the empirical rule2 that, if a polymeric product
remains a commodity material competing for use in
commodity-type applications, then the price that the average
customer is willing to pay for this material will only increase
proportionally to the logarithm of the improvement in its
performance
The main implication of this equation is that whatever is done to improve the performance of a
polymer (blending, incorporation of fillers, lamination, processing in a different way, etc.) must
not be allowed to increase by much the sales price required to make a profit if its improved
performance remains in the commodity product range. We will refer to this fundamental
limitation on the price that the market will be willing to pay for a commodity polymer as the
"commodity trap". It is only if the performance can be increased sufficiently to make the
material competitive for higher-valued specialty applications (thus escaping the "commodity
trap") that a significant price increase can be allowed. A few examples will be provided below.
Car manufacturers are usually reluctant to pay a large price premium (sometimes any price
premium at all) for the improved performance of parts fabricated from engineering plastics
unless they are producing extremely expensive (and prestigious) vehicles such as Rolls Royce
or Ferrari. More generally, automotive consumers are often willing to pay for features that are
noticeable by their five senses (such as more attractive fascia, more comfortable controls,
high-intensity discharge headlights, advanced sound systems and a quiet interior), as well as
for major enhancements in vehicle quality and safety. On the other hand, if the effects of a new
feature or component of a vehicle cannot be "sensed" by the consumer and if it also has no
implications in terms of significantly enhanced real or perceived quality and safety, consumers
will not be willing to pay any price premium for it and cost will be the overriding consideration.
If an inexpensive polymer (such as a polyolefin) can be modified so that its properties become
competitive with those of an expensive engineering plastic, it can escape the "commodity trap"
since new potential applications become possible for it. It can then command a significant
price premium over the "ordinary" (commodity) grades of the polymer. It must, however, still
remain cheaper than the engineering plastic which it displaces in a higher-valued application.
See Figure 2 for a schematic illustration.
Figure 2: Schematic illustration of two situations where
blending and/or compounding are especially attractive from a
commercial viewpoint. The thick vertical brown line
represents the minimum acceptable performance required to
qualify a material for a certain application. The ellipses
represent regions on the "price-performance plane". EP1 is
an expensive engineering polymer that far exceeds the
performance requirements of the application. EP2 is a
cheaper blend or composite of EP1 with less expensive
ingredients, still exceeding the minimum performance
requirements. CP1 is a commodity polymer that does not
meet the performance requirements of the application. CP2 is
a blend or composite of CP1 that exceeds the minimum
performance requirements and can thus be sold at a
substantially higher price.
Most people agree about the desirability of recycling but are unwilling to pay any price
premium at all for plastic parts with enhanced recyclability. As a result, the growth rate of
post-consumer recycling enabled by the use of compatibilization additives has been
considerably slower than it would have been if its environmental benefits really outweighed
economic factors in most people's minds. This is clearly an area where new or improved
compatibilization technologies can make a significant impact.
The effects of market forces summarized above are sometimes modified (on some occasions
drastically) by governmental regulations. Such regulations are most often related to safety or
to environmental benefits. Regulations can involve international, national, or local governing
bodies. They can differ significantly between different regions of the world, such as the United
States and the European Union. They can modify the technologies and products that are
available, as well as the relative costs of the available choices. Examples include
governmental demands for increasing fuel economy and reducing tailpipe emissions in
vehicles and for increasing the amount of plastic recycling. When such changes are mandated
by governments, the cost-effectiveness of useful polymer compatibilization technologies can
change drastically.
Thermodynamic Equilibrium Phase Diagram
The latest edition of a book by Bicerano3 and illustrations of compatibilizer structure and action
posted on the website of SpecialChem were used as the main resources for this subsection.
The rapid screening of possible compatibilizers by predicting how their molecular
architectures, chemical structures and concentrations affect the thermodynamic equilibrium
phase diagram is a challenging but useful starting point. ("Molecular architecture" refers to the
overall pattern of construction of a molecule. For example, a molecule that contains five
subunits of chemical structure A and five subunits of chemical structure B could have its A and
B subunits arranged randomly, or in an alternating fashion as in ABABABABAB, or in "blocks"
of A and B subunit as in AAAAABBBBB, etc.) At present, such relatively routine predictive
screening is only feasible for formulations without reactive components since the techniques
for dealing with complexities introduced by chemical reactions in reactive compatibilization are
less developed.
The fundamentals of compatibilization have been studied for many years, especially for the
equilibrium (thermodynamic) properties. Methods for predicting the phasic behavior of
nonreactive mixtures have advanced tremendously in sophistication and accuracy (and hence
in reliabilty and practical utility) in recent years. It has been shown that, with the proper
selection of the material parameters describing the system components and their mutual
interactions, the same fundamental physical theory can give all observed types of phase
diagrams. Different simulation methods differ mainly in the details the calculation of how the
enthalpy (H) and the entropy (S) change upon mixing. Thermodynamic equilibrium is
determined by the drive towards minimum Gibbs free energy, G=H-TS, where T is the
absolute temperature.
The simplest example involves the calculation of the phase diagrams of binary amorphous
polymer blends. These phase diagrams can be predicted (or can at least be correlated) quite
easily as functions of the chemical structures and molecular weights of the component
polymers by using the Flory-Huggins solution theory. According to this theory, the enthalpy of
mixing ( Hmix) between mixture components A and B (and thus the deviation from ideal mixing
at thermodynamic equilibrium) is proportional to the "binary interaction parameter" AB. The
case of AB=0 indicates ideal mixing where Hmix=0. The very rare case of AB<0 indicates an
enthalpic driving force towards mixing ( Hmix<0). For the vast majority of mixtures, AB>0 (and
hence Hmix>0), indicating that the components enthalpically prefer to be surrounded by other
molecules of their own kind. Larger positive AB indicates stronger enthalpic driving force
towards phase separation. Entropy always favors mixing. The total free energy of mixing,
Gmix, is the sum of enthalpic and entropic terms. For a binary blend of polymers A and B, it is
given by Equation 2, where R is the gas constant, Vtot is the total volume of the two polymers,
Vref is a reference volume (in practice, Vref=100 cm 3/mole is often used), A and B are the
component volume fractions and n A and n B are their degrees of polymerization in terms of
Vref.
Phase separation occurs if AB has a sufficiently large positive value to overcome the entropic
effect. The entropic effect decreases rapidly in relative importance with increasing effective
degree of polymerization n, so that miscibility decreases with increasing n. The product AB?
quantifies the combined effects of degree of polymerization and intermolecular interactions on
miscibility. Equation 3, where d0, d1, d2 and d3 are fitting parameters, can produce all of the
observed types of binary amorphous polymer blend phase diagrams shown in Figure 3. This
equation can be used either correlatively by fitting the theory to experimental data on phasic
behavior or predictively by fitting to the interaction energies predicted by atomistic simulations.
Figure 3: Schematic illustration of possible types of polymer blend phase
diagrams, for binary blends where additional complications that can be
introduced by competing processes (such as the crystallization of a
component) are absent.3 The coefficients d1 and d2 refer to a general
functional form (see Equation 3) for the binary interaction parameter AB.
While most commercially successful compatibilizers are random copolymers, block
copolymers consisting of dissimilar blocks (most commonly, blocks differing greatly in chain
rigidity) have always been viewed as obvious candidates for use as compatibilizers. Each type
of block interacts more favorably with a different polymeric component in the blend. Since the
blocks are connected to each other by covalent bonds, they cannot "get away" from each
other. Consequently, their favorable interactions with and penetration into the phase domains
of dissimilar polymers force these polymers to become more intimately mixed.
Compatibilization is considered to have occurred if the phase domains of the immiscible
polymers in the blend become small enough that the blend can be considered to manifest
"microphase" instead of "macrophase" separation. It is even better if the componenta can be
mixed at the nanoscale.4 The design of nanostructured blends creates opportunities to develop
novel materials whose property profiles can be tailored more precisely for specific applications.
The use of block copolymers as compatibilizers provides the ability to achieve such nanoscale
self-assembly.
The thermodynamics of blend compatibilization by block copolymers have been investigated
extensively by Leibler5 and by Balazs et al. 6,7 These researchers formulated models for
predicting the molecular architecture and composition of effective compatibilizers for any given
binary polymer blend. While Leibler's model can be applied equally to premade and reactive
compatibilizers, the latter have more complexity due to the intriguing interfacial reaction
kinetics. The role of such reaction kinetics in blend compatibilization has been studied both
theoretically (Fredrickson and Milner,8,9 O'Shaughnessy et al.10,11 ) and experimentally
(Macosko et al.12 ) in recent years, but much remains to be done before robust models that can
routinely be used to guide reactive blend design become available. Preliminary data on the
compatibilizing influence of fillers in polymer blends have been reported by Rafailovich et al. 13
(for organoclays) and by Lipatov et al. , 14,15,16 (for silica). This is also an area where much
further work is needed to develop robust models that can truly guide polymer blend as well as
polymer composite design.
In addressing a specific set of problems via modeling, one can usually readily decide which
method is most appropriate. Once a choice is made, a particular experimental and/or modeling
capability to screen additives and processing conditions can generally be found. The ability to
predict the thermodynamic equilibrium mixing behavior in a blend, mixture, or composite with
reasonable reliability helps target experimental work towards the most promising directions.
This statement is valid regardless of the intended application of the blend, mixture, or
composite material. A recent review article on industrial applications of polymer modeling
17
includes some examples of applications of thermodynamic equilibrium mixing considerations.
The three major classes of compatibilizers can be distinguished from each other in terms of
the primary mechanism by which they reduce the interfacial tension between incompatible
polymers and thus favor finer dispersion with more regular and stable equilibrium
morphologies:
Figure 4: Use of a block copolymer for
compatibilization. The block copolymer will prefer to
migrate to the interface to reduce the interfacial
tension. Red blocks are compatible with Polymer A
(matrix). Blue blocks are compatible with Polymer B
(dispersed phase). The consequence will be lower
interfacial tension, better interfacial adhesion and
better dispersion.

Block or graft copolymers (Figure 4).
Figure 5: Use of an nonreactive polymer containing
polar groups for compatibilization by the creation of
nonbonded interactions [in order of increasing
strength, dispersive, polar cohesive and hydrogen
bonding (strongest type of polar cohesive)]. If all else
is kept equal, the stronger and more "specific" the
nonbonded interactions, the higher is the
compatibilization effectiveness. In general, the
compatibilizer must be compatible with one phase
(generally with the nonpolar phase) and must create
specific interactions with the other phase.


Nonreactive polymers containing polar groups (Figure 5).
Figure 6: Use of a reactive functional polymer for
compatibilization. Reaction at the interface between functional
groups on the different polymers creates, "in-situ", a grafted
block copolymer. The functionalized copolymer is miscible with
the matrix and can react with functional groups of the dispersed
phase.


Reactive functional polymers (Figure 6). Many compatibilizers of this class also
contain nonreactive polar groups in addition to reactive groups. Maleic anhydride
(MAH, see Figure 7 for an example of how it works) is the most commonly used type
of reactive group in such polymers. The second most commonly used type of reactive
group is glycidyl methacrylate (GMA, see Figure 8 for an example of how it works)
which introduces epoxy functionalities.
Figure 7: Compatibilization by MAH-grafted reactive functional
polymers. Maleated polymers can be prepared directly by
polymerization or by modification during compounding via the
reactive extrusion process. Their anhydride groups can react with
amine, epoxy and alcohol groups. In this example, the reaction
between a maleated polymer and the -NH2 end groups of
Polyamide 6,6 (Nylon 6,6) compatibilizes a polyamide/polyolefin
blend.
Figure 8: Compatibilization by GMA-grafted (epoxidized) reactive functional
polymers. They react with amine, anhydride, acid and alcohol groups, making them
effective in compatibilizing polar polymers with nonpolar polymers according to the
mechanism shown above.
Some of these types of polymers (especially those containing polar functional groups and/or
reactive groups) are often also effective as coupling agents between polymers and inorganic
fillers in composites (Figure 9) and/or as adhesion promoters between incompatible polymers
in a laminate or between polymers and a substrate such as glass or a metal. In all cases, they
owe their effectiveness to the same fundamental underlying cause; namely, their favorable
effect in modifying the thermodynamic equilibrium state towards which the morphology of the
system will evolve unless its evolution is hampered by kinetic barriers as will be discussed
next.
Figure 9: A polymeric coupling agent
attaches an inorganic filler to the polymer
matrix and thus compatibilizes the filler with
the polymer by nonbonded (physical)
interactions and/or chemical bonds. It must be
compatible with the polymer (ideally, it should
have the same chemistry as the polymer), as
well as being able to interact with, react with,
or even better "glue" to the filler.
Metastable Morphologies Induced by Processing Conditions
The latest edition of a book by Bicerano3 was used as the main resource for this subsection.
The morphology of a polymer blend or composite is often not at thermodynamic equilibrium but
instead at a metastable state that the morphology is "frozen into" as a result of the processing
conditions used in fabrication. Metastability refers to the ability of a system to exist indefinitely
in a state separated by an energy barrier from a thermodynamically more stable state. The
"classic" example is that people often say that "diamonds are forever" although graphite is
thermodynamically more stable than diamond. A diamond will, in fact, become transformed
into graphite if it is heated for a sufficiently long time at a sufficiently high temperature. In
polymer blends and composites, factors that can cause and influence deviations from
thermodynamic equilibrium include the relative viscosities of polymeric components during the
blending process, details of mixing equipment and conditions and post-fabrication physical
aging by annealing.
High shear may produce morphologies that deviate strongly from thermodynamic equilibrium;
broadening greatly the volume fraction range over which phase co-continuity may occur in a
polymer blend. Such morphologies may be "frozen in" by kinetic barriers when the specimen is
cooled. A dramatic example is how the use of optimal melt processing conditions along with
appropriately chosen compatibilizers has led to lamellar co-continuous morphologies, thereby
producing blends whose solvent and gas barrier properties differed drastically from those of
ordinary blends of the same composition.18 In this example, kinetic barriers were used to help
design metastable morphologies with desirable properties. It is also possible to use high shear
to help disperse fillers in polymers and to create morphologies where stiff anisotropic fillers
(such as fibers and platelets) have a preferred orientation.
Annealing tends to coarsen the blend morphology, by reducing the total interfacial area per
unit volume so that the interfacial components of the Gibbs free energy G can be minimized.
Economic value can be gained by the development of combinations of blend or composite
formulations and processing conditions that enable the components to mix well at lower shear
rates. Less sophisticated (and hence less expensive) mixing equipment can then be used to
attain the desired morphology, reducing equipment costs. Energy costs can sometimes also
be reduced, provided that the ability to process at a lower shear rate can be attained without
requiring a substantial increase in the processing temperature. It is also valuable to design
processing conditions that can shorten cycle times and/or enable thin or complex-shaped
objects to be manufactured faster and with better quality. Metastable morphologies induced by
the processing conditions are important in making any of these process improvements.
It is crucial, for promising blend and composite formulations, to explore how the phase
structure depends on the processing conditions. Physical phenomena in polymers take place
over a vast range of length and time scales. Atomistic simulations describe physical processes
whose trea™ent requires the explicit consideration of the atoms. Simulations at the continuum
level describe the behavior of the bulk material. Mesoscale simulation methods (such as
dissipative particle dynamics and dynamic density functional theory) bridge between these two
scales. They describe phenomena taking place at length and time scales that are larger than
atomistic but smaller than macroscopic, such as the collective behavior of chain segments
consisting of several repeat units lumped together into "beads" connected to adjacent "beads"
by "springs". They provide valuable insights on morphology evolution over time in
heterophasic polymer systems. There is, therefore, intense ongoing research to improve their
abilities to predict the dynamic pathway along which the morphology evolves from an initial
state towards thermodynamic equilibrium. Nonetheless, much additional work is needed to
develop reliable rules for predicting (even at a merely qualitative level) kinetic effects on the
phase structure. An empirical "statistical design-of-experiments" approach is, hence, currently
(and possibly for the foreseeable future) most often the best approach for optimizing such
effects.
Practical Implications of Kinetic Barriers to Equilibration
The compatibilization of immiscible polymers is one of the most important, widespread and
difficult problems in contemporary applied polymer science. In investigating various methods
of compatibilizing immiscible blends, one can roughly distinguish two broad types of
approaches:
1. Modification of Processing Conditions. These methods could include:
(a) Increasing the processing temperature.
(b) Increasing the motor speed and/or improving the mixing by some other means.
2. Modification of Polymer Formulation. The additives could include:
(a) "Standard" (premade) compatibilizers.
(b) Reactive compatibilizers.
(c) Other substances (such as silica, carbon, or clay nanoparticles) that may manifest a
compatibilizing effect under some conditions.
Some techniques [such as 1(a), 2(a) and 2(b) and perhaps in many cases also 2(c)] rely on
thermodynamics to "break up" macrodomains and ensure "true" homogeneity of the system.
Other methods [1(b) and 2(c)] rely on kinetics to "break up" domains constantly and force the
system to remain "approximately" homogeneous in metastable morphologies with domain
sizes not exceeding ~1 micron. Several of these techniques are often combined in practice.
For example, it is quite common to increase both the temperature and the shear rate during
processing, while also including both a compatibilizer and other substances in the formulation.
It is difficult to prescribe a priori which method should be used for any particular problem. Each
method has its own advantages and disadvantages. For example:

If it were practically feasible, increasing the processing temperature to the point where
two polymers become miscible would certainly solve thermodynamic incompatibility
problems. However, this solution is impractical for many realistic systems in which the
transition from a two-phase system to a one-phase system occurs far above the
decomposition temperature of one or both components.

Improving mixing can be relatively easy and straightforward, but the mixture can
quickly phase separate into large droplets once shear (a kinetic factor) is removed.

Compatibilizers (such as short chains of block copolymers or random copolymers) can
reduce the interfacial tension to near-zero levels and promote mixing on the
nanoscale. However, this effect is limited by the migration knietics of compatibilizer
molecules towards interfaces and can thus be very slow,.

Reactive compatibilizers rely on chemical reactions that take place during processing
to attach themselves to the polymers that are being blended and thus compatibilize
immiscible polymers with each other. In practice, they can be either more effective or
less effective than standard compatibilizers, depending on the choices of reactive
groups and catalysts.

The addition of lower molecular weight molecules (compatibilizers) sometimes leads
to a dramatic worsening of various properties (such as stiffness, toughness, or flame
retardancy) even if these additives improve the compatibility of the polymers in the
blend.

The addition of nanoparticles may be a useful and interesting method of
compatibilization, but its mechanism is not well-understood and so far there have been
only a few studies describing this effect which is at the frontiers of compatibilization
science and technology.
Morphology-Property Connections
The latest edition of a book by Bicerano3 was used as the main resource for this subsection.
The qualitative connections between polymer blend or composite morphology and mechanical
properties, as well as the mechanisms by which an additive can improve the mechanical
properties, are known. Many additives can often perform multiple roles and sometimes do so
simultaneously in a given polymeric system. Here is a summary of the most commonly found
multiple roles. These roles will be illustrated with many examples in later pages of this report.

A "blend compatibilizer" often also functions as an "impact modifier". The
morphological changes resulting from enhanced compatibility can increase the impact
strength at ambient temperature and also help retain acceptable impact strength at
lower temperatures than is possible in the absence of the additive. These
morphological changes typically are the development of much smaller (in some
instances, interpenetrating) phase domains that are better connected to each other,
enabling improved load transfer across phase boundaries.

If a polymer (or blend) contains reinforcing fillers (such as inorganic fibers), an additive
that can compatibilize the polymers in a blend may also act as a "coupling agent"
between the polymer(s) and inorganic fillers, helping disperse the fillers and bond
them to the polymer(s) and thus increase the stiffness (modulus), strength and impact
toughness of the composite.

A compatibilizer may often also act as an "adhesion promoter" between a polymer (or
blend) and a substrate, or between adjacent layers consisting of dissimilar polymers in
a multilayer structure. Better interlayer adhesion results in better mechanical
properties.
Both analytical (micromechanical) and numerical simulation (most commonly, finite element)
methods for the semi-quantitative prediction of such effects are still under development. For
multilayer systems with good interlayer adhesion and known layer properties, the equations of
lamination theory or numerical simulations can often be used to predict some key properties
quantitatively as a function of the properties and the arrangement of the layers in the laminate.
More generally, the ability to make reliable quantitative predictions remains further in the
future.
In a practical blend or composite design project, it will generally be useful to use the qualitative
and semi-quantitative insights that can be gained from theory and simulations to provide some
guidance to experimental work intended to link the formulations of products of interest to their
final mechanical properties. It will, however, be essential both to verify the qualitative validity of
anticipated connections between morphology and mechanical properties and to quantify these
connections as a part of product design and optimization, by means of careful experiments.
In relation to the mechanical and other properties, it is important to keep in mind when blends
and composites can provide the most value and thus offer the greatest profit potential. It is
when their properties are not simple weighted averages of the properties of their components,
with all of the compromises and tradeoffs inherent in such an average. The best blends and
composites offer far more than just a compromise between the properties of their components.
Instead, they offer synergies whereby the product can provide combinations of performance
characteristics that are unattainable by using any single polymer, at a reasonable price. If an
additive supplier is able to provide compatibilizers that enables certain polymers to blend
better or certain fillers to be incorporated more effectively into polymers and thus provide such
synergistic combinations of properties, it will be rewarded by the market.
Here is an example of what is meant by a synergistic combination of properties. Polymers (just
like other materials) become embrittled as the temperature is lowered. It is highly desirable for
exterior body panels in cars to have high impact strength at very low temperatures. A car
producer would want to be able to sell the same car in Alaska, with comparable safety and
quality attributes, as it is able to sell in Texas. On the other hand, plastic parts used in exterior
body panels are normally painted by the "e-coat" electrostatic painting process where they are
subjected to elevated temperatures for a prolonged period in a baking oven. One needs to
avoid warpage and/or other dimensional changes of a panel during this manufacturing step so
that the polymer must be able to maintain its high stiffness ("modulus") up to very high
temperatures and thus avoid "creep". In other words, the polymer needs to have a very high
"heat distortion temperature". An empirical trend (with fundamental underlying physical
causes) is that the low-temperature fracture toughness (resistance to brittle fracture under
impact) of a polymer decreases with increasing high-temperature stiffness (elastic modulus).
One reason why General Electric's NORYL™ GTX blends have been successful in this
application is that they are able to provide a desirable combination of adequate
low-temperature toughness and high-temperature stiffness, while still remaining at a
reasonable price.
Another interesting example of a synergistic combination of properties comes from the
frontiers of composite materials development, in nanocomposites where the "exfoliation" and
dispersion of highly anisotropic clay platelets with a thickness of ~1 nanometer in
polypropylene is improved by using MAH-grafted polyropylene. For low clay loadings (up to
2.5% by weight), it is observed that the tensile strength, modulus and fracture toughness all
increase substantially. 19
It should be clear by now that any polymeric compatibilizer can potentially also serve as an
impact modifier, if incorporated in the right amount, into an appropriate polymeric system, by
using a suitable processing technique. It is important to emphasize, next, that while all
polymeric compatibilizers thus have the potential to serve as impact modifiers, all polymeric
impact modifiers are not necessarily compatibilizers. It is possible for some polymeric additives
to serve as highly effective impact modifiers in certain polymeric systems without also playing
the role of a compatibilizer. In order to understand this subtle but important distinction, we
must delve deeper into the mechanisms of toughening a polymer by incorporating another
phase in it.
Rubber particle incorporation is a common toughening method. However, voids and even rigid
particles are sometimes used as tougheners. Toughening occurs by imparting either the ability
to craze (in brittle matrix polymers such as polystyrene) or the ability to undergo shear
yielding (in pseudoductile matrix polymers such as Polyamide 6,6) more effectively. It has also
been shown, in work on rubber-toughened polypropylene, that energy dissipation due to
viscoelastic relaxation may sometimes be an additional toughening mechanism. The main
initial role of the inclusion (whether it is a rubber particle, a void, or a rigid particle such as
CaCO3) is to act as a stress concentrator in its vicinity because of the difference between its
stiffness and the stiffness of the surrounding matrix material. The local initiation and then the
propagation of many crazes or shear bands (or both, in polymers which exhibit mixed failure
modes) increases the energy dissipation required to cause failure so that the polymer
becomes "tougher". The optimum rubber phase morphology correlates with the nature of the
matrix phase. The extent to which a polymer can be toughened at a given rubber volume
fraction depends on its intrinsic toughness:

For brittle (crazing) thermoplastic matrix polymers, the controlling parameter is the
optimum rubber particle size. This parameter decreases with increasing matrix
ductility, so that if the matrix polymer is less brittle then smaller rubber particles may
be able toughen it.

For pseudoductile (shear yielding) thermoplastic matrices, the controlling parameter is
the critical average distance between the surfaces of two neighboring rubber particles.
This parameter increases with increasing matrix ductility, so that if the matrix polymer
is more ductile then rubber particles that are further apart from each other may be able
to toughen it.

Much work has been reported on the quantification of these trends in terms of intrinsic
characteristics of polymers (such as characteristic ratio and entanglement density),
the morphologies of polymers (such as the effects of crystallinity), and characteristics
of the particles of the second phase (volume fraction, size distribution and spatial
distribution).

It has also been found that rubber-toughenable thermosets with high glass transition
temperature (Tg) are more readily obtained if the high Tg is attained by enhancing the
chain stiffness than if it is attained by increasing the crosslink density.
It should be clear from the paragraph above that many entities can act as impact modifiers
without serving as compatibilizers. These entities include rubber particles (which are
polymers), and in some instances voids or even rigid particulate fillers. Such entities can
"toughen" a polymer without playing any role in compatibilizing immiscible polymers, in
coupling polymers to fillers, or in helping enable the adhesion of dissimilar materials in
laminates. The focus of this report is on compatibilization technologies. Consequently, while
many examples of impact modification by compatibilizers will be highlighted to provide a
complete perspective of their versatility as additives, we will not discuss impact modifiers
which are not also compatibilizers.
Overveiw of Available Compatibilization Technologies
The information provided in this section was assembled through extensive searches on the
worldwide web which has become the best available source of product information. Most
companies provide detailed information online regarding their products, often including case
studies describing the use of their products and/or citations to relevant articles in the open
literature. There are also many online databases [such as SpecialChem (which contains a very
extensive additives database), Omnexus, MatWeb, CAMPUS and IDES Prospector] of
commercial polymers, blends and additives. These databases all provide free access to their
compilations, but some require the payment of fees to gain access to their "premium content".
The author considered whether to list the URLs of the many worldwide web pages from which
information was extracted and decided not to list them. Unlike a book or a journal article, URLs
are quite ephemeral. They can change and/or be removed at any time, potentially resulting in
considerable frustration and waste of time for a person looking for them a year or two after
they were cited. Readers interested in more detailed information about the products discussed
in this section are recommended, instead, to visit the most current websites of the online
databases named above and of the companies named below.
Companies sometimes change identity because of events such as mergers and acquisitions.
Furthermore, product lines are sometimes sold from one company to other. Trademarks
generally outlive such events. Consequently, searching the worldwide web by using the
tradename of a product as a keyword may also be a good strategy to find the most recent
information about a product line a few years after the completion of this report.
Company
Product
Tradename
MODIFIED POLYOLEFINS
Ethylene-VAc-CO (CO denotes carbon monoxide),
ethylene-BA-CO and ethylene-BA-GMA terpolymers; ethylene-MA,
ethylene-EA and ethylene-BA copolymers.
Elvaloy
DuPont

Use of CO as a comonomer results in the incorporation
of -C(O)- (ketone) groups along the chain backbone.
DuPont
A very broad range of MAH-grafted polyolefins.
Fusabond
Ethylene-methacrylic acid (MAA) ionomers. Zn2+ or Na+ is used as
the counterion in the different product grades.
DuPont


DuPont
Surlyn
MAA repeat unit: -CH2-C(CH3)(COOH)-.
Anionic MAA repeat unit: -CH2-C(CH3)(COO-)-.
Poly(vinyl alcohol), repeat unit: -CH2-CH(OH)-.
Elvanol
STYRENIC BLOCK COPOLYMERS
BASF
Styrene-butadiene (SB) diblock copolymers.
Styrolux

BASF
B repeat unit: -CH2-CH=CH-CH2-.
Styrene-butadiene-styrene (SBS) triblock copolymers.
Styroflex
Styrene-butadiene-styrene (SBS) and styrene-isoprene-styrene
(SIS) triblock copolymers.
VECTOR
Dexco Polymers

I repeat unit: -CH2-CH=C(CH3)-CH2-.
SBS and SIS triblock copolymers, their hydrogenated midblock
Kraton Polymers
versions and their hydrogenated midblock versions grafted with
KRATON
functional groups such as MAH. .
SBS and SIS triblock copolymers (hydrogenated B or I block).
Kuraray

SEPTON
See Figure 22 for the chemical structures.
OTHER TYPES OF COMPATIBILIZERS
Degussa
Methacylate-based polymeric compatibilizers.
DEGALAN
Polycaprolactone (PCL) polyesters, PCL polyester /
poly(tetramethylene glycol) (PTMEG) block polyols.
Dow Chemical
Polymer
Chemistry
Innovations
TONE

PCL repeat unit: -(CH2)5-COO-.

PTMEG repeat unit: -(CH2)4-O-.
Methacrylate-terminated reactive polystyrene.

Methacromer
See Figure 27 for the chemical structure.
Mixture of aliphatic resins with a molecular weight below 2000
STRUKTOL
Struktol
g/mole, blend of medium molecular weight resins.
Table 2: A representative (but not comprehensive) selection of polymeric compatibilizer suppliers and
their products, some acronyms used in this report, and trade names for the products. The products
listed below will be discussed further in Section 4.
Table 2 lists the companies and products that will be discussed further in providing examples
of the use of polymeric additive technologies. The information provided in Table 2 is intended
to constitute a representative sampling of the types of additive technologies and is not (nor
was it intended to be) a comprehensive listing. The suppliers of polymeric compatibilizers cited
in Table 2 will be discussed in the next section, in alphabetical order. It is hoped that sufficient
detail will have been provided in this broad survey to give the reader a good idea of the type of
additive product that may be most appropriate for his/her needs and thus focus further effort.
The largest number of polymeric compatibilizers, by far, are the modified polyolefins.
Polymeric additives manufactured by DuPont are used in this review to provide illustrative
examples of such additives and their utility. Most types of modified polyolefins contain polar
groups that enhance their compatibility with polar polymers, and their abilities to couple to (and
disperse) inorganic fillers more effectively and to adhere to substrates. In some modified
polyolefins, some or all polar functional groups are reactive. Reactive functionalities may
further strengthen the effectiveness of an additive by creating chemical bonds to a polar
polymer, filler, or substrate. The abundance of competing modified polyolefin additive
technologies from many vendors reflects the tremendous commercial importance of the
polyolefins as inexpensive commodity polymers that can be used for a wide range of
applications. The importance of polyolefins has been growing in recent years. This trend is
driven both by advances in catalyst technology that have made it possible to "tailor" polyolefins
more precisely than was possible in the past and by the desire to expand the use of polyolefins
in applications where the incumbent materials are much more expensive engineering
thermoplastics.
Styrenic block copolymers constitute the second largest general class of compatibilizers.
These thermoplastic elastomers have hard blocks that segregate into a glassy glassy hard
phase and soft blocks that segregate into a rubbery soft phase. The growth of this technology
(as illustrated here in the context of products from BASF, Dexco Polymers, Kraton Polymers
and Kuraray) is a result of the synergistic superposition of three key factors that encourage
intense research and development activity towards its continued development:
1. These types of block copolymers have many important applications on their own right, in
addition to their use as additives.
2. Polystyrene is a relatively inexpensive commodity polymer that has a very broad range of
applications. Consequently, new additives that improve its properties and/or allow it to be
blended with a broader range of polymers will be valuable.
3. Advances in anionic polymerization technology, as well as in the ability to predict the effects
of molecular architecture on the properties of a block copolymer, have resulted in the ability to
"tailor" styrenic block copolymers increasingly more precisely for targeted applications.
Other types of commercially available polymeric compatibilizers include methacrylate-based
polymers (Degussa), polycaprolactone polyesters and polycaprolactone / poly(tetramethylene
glycol) block polyols (Dow Chemical), methacrylate-terminated reactive polystyrene (Polymer
Chemistry Innovations), and mixtures of aliphatic resins of low or medium molecular weight
(Struktol).
Automotive and electrical/electronic applications provide the broadest range of opportunities
for new polymeric compatibilizers; as blend compatibilizers, coupling agents, adhesion
promoters and/or impact modifiers. Significant opportunities also exist in the packaging, major
appliance, sports/recreation equipment and medical device industries; and in the continued
development of plastics recycling technologies.
Representative Examples of Vendors and Their Technologies
BASF
Figure 10: Characteristics and applications of BASF's Styroflex SBS triblock copolymers.
BASF makes the Styrolux™ styrene-butadiene (SB) diblock and Styroflex™
styrene-butadiene-styrene (SBS) triblock copolymers. These polymers have many important
applications on their own right, in addition to being useful as polymer blend compatibilizers and
as impact modifiers in polymers (especially polystyrene) and blends. See Figure 10 for the
characteristics and applications of Styroflex. Such versatility is also shared by the styrenic
block copolymers (SBCs) of other manufacturers (discussed later) and enhances the growth of
SBC technology.
Degussa
The DEGALAN™ products of Degussa are specially-designed thermoplastic
methacylate-based polymeric compatibilizers for polymer blends. Acrylic polymers typically
manifest excellent resistance to UV light and saponification, colorfastness and durable gloss
and good chemical resistance. The selection of suitable methacrylic comonomers makes it
possible to obtain coating systems with excellent resistance, especially to outdoor exposure.
Coatings manufactured according to standard formulations do not yellow even after prolonged
weathering and show no change in color. They are also remarkable for their durable high gloss
and very low tendency to chalking. Applications include heat-seal lacquers, PVC finishes,
concrete coatings, marine and container paints, low-odor interior paints, metal coatings,
printing inks, exterior paints, ceramic transfer lacquers and halogen-free plastisols.
Dexco Polymers
Dexco Polymers is a joint venture between Dow Chemical Company and ExxonMobil
Chemical Company. It makes VECTOR™ styrene-butadiene-styrene (SBS) and
styrene-isoprene-styrene (SIS) triblock copolymers, which are thermoplastic elastomers, via
anionic polymerization.
Different VECTOR polymer grades differ in their relative amounts of rigid (polystyrene) and
soft (polybutadiene or polyisoprene) blocks, molecular weights, molecular architecture
(whether the arrangement of the blocks is linear or radial), whether any residual diblock
copolymer is present, whether any other component is present and/or the physical form in
which the product is supplied (pellet or powder). These differences cause variations in
properties and processing characteristics. For example, increasing molecular weight generally
improves mechanical properties but reduces the ease of melt processing. Increasing the
relative amount of the rigid blocks results in a stiffer (higher modulus) polymer. Any change in
the composition or molecular architecture can also alter the thermodynamics and kinetics of
mixing with other polymers and thus affect the action of these polymers as blend
compatibilizers and/or impact modifiers.
VECTOR block copolymers are used by producers and compounders of olefinic and styrenic
thermoplastics, engineering resins, thermosets, blends and alloys, to enhance the toughness
and impact strength of such materials at ambient and low temperature. When used in blends,
they enhance the compatibility between appropriate types of dissimilar polymers (such as
styrenic polymers and olefinic polymers). Diblock-free grades also extend the
high-temperature performance range of the modified base resin compared to conventionally
polymerized styrenic block copolymers containing diblock residues. Some grades can be used
as base feedstocks for the manufacture of more advanced engineering resins. Others are
tailored to overcome the deleterious effects of additives such as flame retardants. The superior
heat resistance of halide-free VECTOR grades manifests itself in in the improved color stability
of the base resin and is especially evident after multiple-heat exposures of in-plant recycle.
Some VECTOR grades may be qualified for certain food contact and/or medical applications.
The recycling of plastics (where compatibilization of dissimilar polymers is of crucial
importance) is another focus of product development activities. For homogeneous recovered
plastics, VECTOR block copolymers can renew the properties, resulting in near-virgin product
performance.
The VECTOR grades available as of the date of this report are 2411, 2411P, 2518, 2518P,
4461, 6241, 6507, 7400 and 8508 (SBS); and 4111A, 4113A, 4114A, 4211A, 4215A, 4230 and
4411A (SIS). The product grades containing the letter "P" (2411P and 2518P) are provided as
powders while the other grades are provided as pellets. The following grades include a diblock
copolymer component: 2411, 2411P, 4113A, 4114A, 4215A and 4230. In VECTOR 7400, a
linear, pure SBS triblock copolymer is extended with 33% mineral oil. The molecular
architecture is radial in VECTOR 2411, 2411P and 4230; and linear in the other grades.
Dow Chemical Company
The TONE™ polycaprolactones are truly biodegradable when composted and thus of special
interest when biodegradability is desired. TONE P-767 and P-787 are linear polycaprolactone
polyesters with high crystallinity and a low melting temperature, used in various thermoplastic
blend applications. They have broad miscibility or mechanical compatibility with many
polymers (see Table 3), resins and pigments. Applications include use as dispersants,
compatibilizers and reactive modifiers for other polymers such as polyesters and nylon fibers.
TONE P-767 can be injection molded, extruded, slot-casted into films, or blended with other
polymers. It is available in pellet or powder form. TONE P-787 can be extruded or blended with
other polymers. It was specially formulated for use in high melt strength thermoplastic
applications.
Poly(vinyl chloride) (PVC), poly(styrene-co-acrylonitrile) (SAN, 24 % to 29 %),
poly(acrylonitrile-co-butadiene-co-styrene) (ABS), polydroxyether of bisphenol-A,
Miscible
phenoxy resin, polycarbonate, nitrocellulose, cellulose butyrate, cellulose
propionate, chlorinated polyether, polyepichlorohydrin, poly(vinylidene chloride),
styrene/allyl alcohol copolymers.
Polypropylene, poly(1-butene), polyethylene, natural rubber, styrene/butadiene
Mechanically
elastomers, styrene/butadiene block copolymers, unsaturated polyesters, epoxies,
Compatible
phenolics, poly(vinyl acetate), poly(vinyl butyral), polybutadiene, ethylene/propylene
rubber, polyisobutylene, polyoxymethylene, polyoxyethylene.
Table 3: Miscibility and compatibility of polymer blends containing poly( -caprolactone).
The TONE polyol-based urethane product family consists of grades which are either liquids at
room temperature (25°C) or have melting temperatures not too far above it. They can be
formulated for adhesion to various substrates at ambient and at elevated temperatures. The
applications of TONE 7241, a linear polycaprolactone polyester / poly(tetramethylene glycol)
(P™EG) block polyol designed for use in elastomers and microcellular systems with enhanced
flex-fatigue performance and hydrolytic stability, include polyol blend compatibilization.
DuPont
DuPont makes four product lines of functionalized polyolefins. The many applications of these
materials include polymer blend compatibilization, coupling of polymers to fillers, promotion of
adhesion of polymers to substrates as well as to dissimilar polymers in multilayer structures
and impact modification of polymers. Different grades of each product line are optimum
choices for use in different applications. Many of these polymers meet the requirements of the
Food and Drug Administration of the USA for use in a number of regulated applications.
Elvaloy™ ethylene-VAc-CO (VAc: vinyl acetate, CO: carbon monoxide), ethylene-BA-CO and
ethylene-BA-GMA terpolymers; and ethylene-MA, ethylene-EA and ethylene-BA copolymers,
can toughen (impact modify) and flexibilize (plasticize) other polymers. Because of their high
molecular weights, unlike conventional plasticizers, they do not migrate to the surface and
hence are not lost through evaporation or extraction. They can flexibilize and toughen many
polymers; such as PVC, ABS, polypropylene, PET, PBT and polyamides. They also serve as
compatibilizers in polymer blends and coupling agents between polymers and fillers.
Fusabond™ MAH-grafted polyolefins include modified conventional as well as metallocene
polyethylenes, ethylene propylene rubbers, polypropylenes, ethylene-BA-CO terpolymers and
ethylene-VAc copolymers. They are used as coupling agents between polymers and fillers and
as high-performance impact modifiers for engineering polymers. Each grade offers its own
specific interpolymer adhesion characteristics. Their functionalization makes them effective in
helping bond together polymers used in toughened, filled and blended compounds. For
example, MAH-grafted polyolefins can compatibilize and thus help blend, polyamides with
polyolefins. Polyamide-polypropylene blends that can be made by using such compatibilizers
can be used in applications such as parts for automotive cooling systems. Such applications
require the high-temperature properties of the polyamide. However, since moisture absorption
can degrade the polyamide, polypropylene is also needed to reduce moisture absorption. The
Fusabond coupling agents can also provide new levels of functionality in polymer-wood
composites and in other wood alternatives.
Surlyn™ ethylene-methacrylic acid ionomers (with Zn2+ or Na+ used as the counterion in the
different product grades) provide impact toughness, abrasion resistance and chemical
resistance various consumer and industrial products. They can either be used by themselves
or blended with other polymers. They can be injection-molded, extruded, foamed,
thermoformed, or used as a powder-coatings or resin modifiers. The resulting applications
range from tough, cut-resistant golf ball and bowling pin covers, to footwear components,
glass coatings, abrasion resistant surfaces and buoys. Their high resistance to chemicals and
oils enables them to provide unique packaging options for perfumes and cosmetics.
Polymer Blend
Compatibilizer
DuPont's Recommendations
PA6/PE
PE-g-MAH, E-MAA (Zn)
Fusabond E, Surlyn 1652
PA6/PP
PP-g-MAH
Fusabond P
PBT/PP
Ethylene-BA-GMA
Elvaloy PTW
PBT/PA
Ethylene-BA-GMA
Elvaloy PTW
PET/Polyolefin
Ethylene-BA-GMA
Elvaloy PTW
PC/ABS
Ethylene-Acrylate
Elvaloy AC, Elvaloy PTW
PC/PBT
Ethylene-Acrylate
Elvaloy AC, Elvaloy PTW
Table 4: Some important types of polymer blends and both the best generic compatibilizer chemistries
and the compatibilizers recommended by DuPont for each of them. PA6 denotes Polyamide 6 (Nylon
6). PC denotes polycarbonate.
Figure 11: Example showing the finer dispersion and more regular
and stable morphologies that can result from compatibilization. Both
micrographs show the morphology of a blend of 30% Polyamide 6
with 70% linear low-density polyethylene. A grade of Fusabond has
been used at a level of 10% as a polymeric compatibilizer in one of
the two samples.
Table 4 lists some important types of polymer blends and provides both the best generic
compatibilizer chemistries and the compatibilizers recommended by DuPont for each of them.
Compatibilization reduces the interfacial energy between two polymers and thus increases the
adhesion between them. Compatibilizers also generally provide finer dispersion, more regular
and stable phase morphology, better mechanical properties, improved surface characteristics
and enhanced recyclability. Figure 11 shows a dramatic example of the finer dispersion and
more regular morphologies that can result from the addition of a suitable compatibilizer.
Figure 12: Effects of using a small amount of Elvaloy as an impact modifier in
polymers. (a) PC(50)/PBT(50)/Additive(10) blend compared with PC(50)/PBT(50).
Effect the choice of impact modifier on notched Izod impact strength at room
temperature (23 °C) and at 0 °C. (b) Great increase in impact strength of PVC, with
negligible reduction in heat distortion temperature.
Figure 12 shows the effects of using a small amount of Elvaloy as an impact modifier. Figure
12(a) illustrates how an additive can often perform more than one role in a blend. Various
grades of Elvaloy, which compatibilize polycarbonate (PC) with poly(butylene terephthalate)
(PBT), also serve as impact modifiers in PC/PBT blends. It can also be seen that, while the
use of any of these additives improves the impact strength compared with the
uncompatibilized blend, various grades differ drastically in the magnitude of their
effectiveness. This example thus also illustrates the need to select the specific product grade
within a given additive product line very carefully to obtain the desired level of properties at the
lowest possible cost. Figure 12(b) shows that a small amount of suitable grade of Elvaloy can
improve the impact strength of poly(vinyl chloride) (PVC) drastically with very small reduction
in the heat distortion temperature.
Figure 13: General structure of a multilayer film (laminate).
Multilayer structures ("laminates", see Figure 13) are used in many packaging applications.
The combination of layers generally provides a mix of the individual performances of the
polymers involved (such as barrier, sealability, moisture or chemical resistance and stiffness)
that is usually impossible to achieve with a single polymer. The recyclability of the resulting
multilayer material is also desired. The interlayer compatibilization of multilayer.polymeric
materials (such as Polyamide/PE, Polyamide/EVOH/PE, PE/EVOH/PP, PE/EVOH/PE and
PET/PE) is, hence, crucial. Functionalized polyolefins are very useful in such "adhesion
promoter" applications.
Elvanol™ 71-30 is poly(vinyl alcohol). It is prepared in aqueous solutions. Transparent films
with high tensile strength, tear resistance and barrier properties are formed upon evaporation
of water. Elvanol 71-30 provides excellent adhesion to porous, water-absorbent surfaces. It
also provides a combination of excellent film forming and binder characteristics. Its
applications are in adhesives, paper and paperboard sizing and coatings, textiles, films and
building products.
Kraton Polymers
KRATON Polymers makes both clear and oil-extended grades of its styrenic block
copolymers, which are thermoplastic elastomers.
KRATON D polymers are elastic and flexible. The choice of soft block influences the
properties. For example, styrene-butadiene-styrene (SBS) is especially suitable for footwear
and for the modification of bitumen/asphalt, while styrene-isoprene-styrene (SIS) is preferred
for the production of pressure-sensitive adhesives.
The middle blocks of SBS and SIS can be hydrogenated to make KRATON G block
copolymers. These polymers include styrene-ethylene/butene-styrene (SEBS) and
styrene-ethylene/propylene-styrene (SEPS). KRATON G block copolymers have the added
benefits of enhanced oxidation and weather resistance, higher service temperatures and
increased stability during processing by common thermoplastic processing technology. Their
applications include use as sealants and high performance adhesives.
KRATON FG polymers are KRATON G polymers that have been grafted with functional
groups such as maleic anhydride. KRATON FG polymers can manifest improved adhesion to
polar substrates such as metals and polyamides. They can be used as impact modifiers for
polar polymers such as polyesters, polyamides and epoxies. They can also help compatibilize
polyamides and thermoplastic polyesters with polyolefins.
Kuraray
Figure 14: Four types of SEPTON block copolymers: (Top left) Hydrogenated
poly(styrene-b-isoprene) [polystyrene-b-poly(ethylene/propylene) (SEP)]. (Top right)
Hydrogenated poly(styrene-b-isoprene-b-styrene)
[polystyrene-b-poly(ethylene/propylene)-b-polystyrene (SEPS)]. (Bottom left)
Hydrogenated poly(styrene-b-butadiene-b-styrene)
[polystyrene-b-poly(ethylene/butylene)-b-polystyrene (SEBS)]. (Bottom right)
Hydrogenated poly(styrene-b-isoprene/butadiene-b-styrene)
[polystyrene-b-poly(ethylene-ethylene/propylene)-b-polystyrene (SEEPS)]4 . Each type of
polymers has its own unique set of properties.
Kuraray uses its isoprene technology to make the SEPTON™ hydrogenated styrenic block
copolymers (Figure 14), which are thermoplastic elastomers.
Figure 15: Main structural and morphological features of the SEPTON hydrogenated
styrenic block copolymers made by Kuraray. The styrenic block copolymers made by
other companies (such as BASF, Dexco Polymers and Kraton Polymers) also possess
similar general features.
Prior to processing, the polystyrene end blocks are associated in rigid domains. In the
presence of heat and shear (such as the shear imposed during processing), the polystyrene
domains soften and permit flow. After cooling, the polystyrene domains reform and harden,
locking the rubber network in place. This physical phenomenon provides SEPTON its high
tensile strength and its elasticity. These general features are illustrated in Figure 15.
Figure 16: Scanning Electron Micrographs (×1000), illustrating
compatibilization by SEPTON.
When blended with polyolefins, SEPTON improves various properties, including the impact
strength. It can also compatibilize polyolefins with polystyrenes. In the Kuraray product
literature, examples are given of the use of SEPTON as a polypropylene impact modifier and
as a compatibilizer in blends of polypropylene with ABS. The much better mutual dispersion of
ABS and polypropylene in the blends using a SEPTON compatibilizer can be seen from the
micrographs shown in Figure 16.
Property
ABS(70)/PP(30) ABS(70)/PP(30)/SEPTON(5)
Notched Izod (J/m)
49
88
Unnotched Izod (J/m)
167
549
Flexural Modulus (MPa)
2040
1980
Table 5: Data from Kuraray, showing how its SEPTON 2104 compatibilizer, when added at a level of
5% by weight, improves the impact strength of a 70/30 blend of ABS and polypropylene (PP) at room
temperature (25 °C) drastically while causing only negligible loss in stiffness.
The data listed in Table 5 show that the notched and unnotched Izod impact strength both
increase drastically as a result of the improved morphology resulting from compatibilization,
while the loss in stiffness (as measured by the flexural modulus) is negligible. This example,
therefore, also illustrates how an additive can perform multiple roles. SEPTON clearly serves
both as a compatibilizer (Figure 16) and as an impact modifier (Table 5) in this particular blend.
Polypropylene
100 80
80
80
SEPTON 2004
0
20
0
0
SEPTON 2007
0
0
20
0
Ethylene-Propylene Rubber
0
0
0
20
Izod Impact Strength (J/m, at 25 °C) 117 614 547 164
Izod Impact Strength (J/m, at -20 °C) 38.5 141 122 90
Flexural Modulus (MPa)
752 572 671 656
Flexural Strength (MPa)
23.3 18.3 19.3 18
Table 6: Data from Kuraray, showing tremendous improvements in the Izod impact strength of
polypropylene at both ambient and low temperatures with the use of SEPTON 2004 or SEPTON 2007
as an impact modifier. Formulations are indicated in terms of the percentages of their ingredients by
weight. There are only small reductions in flexural modulus and strength. Note that SEPTON is far
more effective than ethylene-propylene rubber as an impact modifier.
Table 6 shows tremendous improvements in the Izod impact strength of polypropylene at both
ambient and low temperatures, with only small reductions in flexural modulus and strength.
Polymer Chemistry Innovations Inc.
Figure 17: Chemical
structure of
Methacromer™ PS12
reactive polystyrene.
More than 85% of the
polymer chains are
terminated with a
methacrylate group.
Polymer Chemistry Innovations Inc. makes the Methacromer™ PS12 methacrylate-terminated
reactive polystyrene. The chemical structure of this polymer is shown in Figure 17. Its physical
properties resemble those of polystyrene woth a low molecular weight. It allows formulators to
modify polymers with a high degree of control. It is especially attractive to adhesive
manufacturers since it can be used to increase the shear strength with only minor effects on
the peel strength. It is available in a standard molecular weight range of 11,000 to 15.000
g/mole, with 12,000 g/mole as the target molecular weight. The molecular weight can be
modified to meet individual specifications. The polydispersity is low: [(Mw/Mn)<1.1]. More than
85% of the polymer chains are terminated with a methacrylate group. It reacts readily with the
acrylates and acrylamides, imparting toughness while keeping the polymer thermoplastic.
Struktol
Struktol's product line of STRUKTOL™ polymer additives includes the STRUKTOL TR product
grades (among which TR 060 and TR 065 can be considered primarily as compatibilizers), as
well as the more recently developed STRUKTOL TPW product grades.
TR 060 and TR 065 are normally incorporated at low levels (0.5% to 1 %) into a formulation.
They both meet the requirements of the Food and Drug Administration of the USA for use in a
number of regulated applications.
TR 060 is a mixture of light-colored aliphatic resins with a molecular weight below 2000
g/mole. It has good solubility in aliphatic, aromatic and chlorinated hydrocarbons. It is a
compatibilizer and blending aid that reduces splay in colored and/or filled polyolefins. It is
very compatible with the polyolefins. It can be used to increase extrusion output rates. It has a
natural tackiness at process temperatures. This "adhesive" nature enables it to act as an
effective binder. This is especially important in polymers where high filler levels require the
most uniform blending in order to maintain or improve the physical properties. In addition, its
low molecular weight provides some viscosity reduction during processing, improving the flow
characteristics. TR 060 has been shown to improve the blending of thermoplastic olefin (TPO)
compounds, flame retardant formulations and filled polymer systems. In general, it is
recommended for use with polyolefins, ABS, styrene-acrylonitrile (SAN) copolymers,
general-purpose polystyrene, high-impact polystyrene, rigid poly(vinyl chloride) (PVC) and
polyesters such as poly(ethylene terephthalate) (PET) and poly(butylene terephthalate) (PBT).
TR 065 is a blend of medium molecular weight resins designed as a high temperature process
aid and blending agent. It works up to process temperatures of 370°C. Its compatibilizing
action is useful in blending polymers, processing recycle materials and incorporating impact
modifiers. It is effective in binding filler materials to the polymer system by virtue of its adhesive
nature at process temperatures. In many cases, especially when high filler levels are involved,
this more homogenous blend results in better physical properties and fewer processing
problems. Its components make it compatible with many polymers, whether polar or nonpolar
in nature. In general, it is recommended for use with polyesters such as PET and PBT,
polyamides, nitriles, PVC, ABS, SAN and general-purpose or high-impact polystyrene.
The new STRUKTOL TPW product grades are polymeric additives that have been developed
specifically for the improved processing of wood-filled thermoplastics. While they can be
viewed primarily as lubricants, their roles also include compatibilization. For example, the
general purpose grade (TPW 101), which consists of a mixture of zinc stearate and waxes,
can improve the processing characteristics of highly filled polyolefin compounds, as well as
improving filler dispersion and providing metal release for both molding and extrusion
operations. TPW 113, which is a blend of complex modified fatty acid esters, can provide
superior filler wetting and dispersion characteristics in a wide range of polymer systems.
Technology Outlook
The development of polymer blends, composites and laminates is of great economic
importance for the plastics industry and for other industries where the use of such products is
becoming increasingly common. Advanced polymer modification techniques have grown in
importance during the last two decades as the "point of diminishing returns" has been
approached in improving the performance/price balance by altering just the chemical
structures of polymers.
The most important polymer modification techniques are blending dissimilar polymers,
preparing composites where a matrix polymer is modified by fillers, and creating multilayer
(laminate) structures. The objective is to seek synergies between the components so that one
can attain better performance without increasing cost or maintain acceptable performance at
lower cost.
Polymeric compatibilizers are polymers that can be used (normally in small percentages) as
additives to help assemble dissimilar components into polymer blends, composites and
laminates with improved properties. These more attractive properties generally result from
phase separation on a finer scale (microscale or even better nanoscale, instead of
macroscale) along with stronger interconnections between phase domains. Impact
modification (toughening) is one major benefit that can often be attained by using polymeric
compatibilizers. It can be inferred from the anticipated continued growth of markets for
polymer-based heterophasic products that polymeric compatibilization technologies will also
contine to grow in importance.
The five key factors that every compatibilization additive developer must consider in order to
improve the likelihood of achieving technical and commercial success simultaneously are (1)
performance versus price, (2) thermodynamic equilibrium phase diagram, (3) metastable
morphologies often induced by processing conditions, (4) practical implications of kinetic
barriers to equilibration and (5) morphology-property-connections. Progress in the
development of predictive methods based on theory and simulation was summarized.
Methods for the prediction of the thermodynamic behavior of nonreactive systems are quite
well-established. Significant further progress is needed for the development of more robust
models for the thermodynanmic equilibrium state of reactive systems, for the dynamic
behavior of both nonreactive and reactive systems, and for the relationships between
morphology and mechanical properties under large deformation. While major progress can be
anticipated in all of these "frontier" areas of materials science over the next decade, a
semi-empirical approach will be most useful in the practical development of new technologies
for the foreseeable future.
The largest number of polymeric compatibilizers, by far, consist of modified polyolefins, most
of which contain polar groups and some of which also contain reactive groups. Styrenic block
copolymers, which are thermoplastic elastomers, constitute the second largest class of
polymeric compatibilizers. Other commercial polymeric compatibilizers include
methacrylate-based polymers, polycaprolactone polyesters, polycaprolactone polyester /
poly(tetramethylene glycol) block polyols, methacrylate-terminated reactive polystyrene, and
mixtures of aliphatic resins of low or medium molecular weight.
Significant progress can be anticipated over the next decade in the development of more
refined grades (tailored for specific applications) of both modified polyolefin and styrenic block
copolymer (and perhaps also selected non-styrenic block copolymer) technologies. A major
guiding principle for such work will be the desire to attain control over the resulting morphology
at an increasingly finer scale. The development of compatibilizers for biodegradable
polymer-based systems (a relatively minor area at this time) may also grow if the
environmental and regulatory driving forces towards biodegradable polymer technology
development gain strength.
Many companies are in the polymeric compatibilizer market with products falling into the
same two major classes (modified polyolefins, styrenic block copolymers) competing for
similar types of applications so that competition is fierce. On the other hand, these are
currently also the two most versatile polymeric compatibilizer families. The markets for other
types of polymeric compatibilizers (where the competitive landscape is less crowded) are more
limited.
Customized additive compunding services are provided by many companies. Organizations
that provide such services range from the technical service depar™ents of giant multinational
corporations to small specialty compounding shops. Customized compounders can provide
complete technology solutions and hence great value to their customers. It is anticipated that
such specialized services (the detailed discussion of which fell outside of the scope of this
review of polymeric compatibilizer products) will also continue to grow over the next decade.
Automotive and electrical/electronic applications provide the broadest range of opportunities
for new polymeric compatibilizers; as blend compatibilizers, coupling agents, adhesion
promoters and/or impact modifiers. Significant opportunities also exist in the packaging, major
appliance, sports/recreation equipment and medical device industries. The continued
development of plastics recycling technologies may also stimulate the growth of
compatibilization technologies if it becomes driven by stronger environmental and regulatory
forces in the future.
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