Molecular architecture
Polymer properties depend on molecular
architecture (the structure of the molecules) and
the physical state of the polymer.
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HOW DO WE DEFINE
MACROMOLECULAR
ARCHITECTURE?
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Macromolecular architecture
• Constitution: type of atoms in the chain (backbone), type of
side groups/branch groups, type of end groups, monomer
sequence, molecular weight distribution
• Configuration: arrangement of neighboring atoms along the
backbone or chain segments
• Conformation: the arrangement of the chain in space
Constitution and configuration are usually set in the polymerization
and/or blending processes.
Conformation is a product of the polymer’s environment.
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BR-PE.avi
BR-PE_2.avi
1_butene.avi
1_butene_2.avi
CASE STUDY: LDPE
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Low density polyethylene
Constitution
• The high pressure synthesis of LDPE via free radical reactions was one of
the first commercial processes at supercritical conditions for the solvent
(ethylene is near or above Tc).
• Constitution: polymerized from ethylene monomer in a process initiated
by free radicals. Some oxygen in the monomer accelerates the process.
Other free radical initiators can be used.
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Low density polyethylene
Configuration
• Statistically, local rearrangements of the chain near the free radical chain
end results in short chains being formed (15-25 per 1000 monomer units;
2 – 8 carbon atoms long)
• This product has similar properties to ethylene/a-olefin copolymers with
0.25 mol % a-olefin.
• Some long chain branching also occurs (0.5 – 4 per 1000 monomer units
long).
• Both types of branching interfere with crystallite growth and structure.
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Low density polyethylene
Conformation
• Arrangement of the backbone and side chains in 3-D.
• In dilute solution, the C-C backbone will be in the zig-zag conformation,
i.e., for carbon atoms lying in the same plane.
• This particular conformation represents a local state of low energy for the
chain; which can be calculated using conventional molecular dynamics
methods
• Branches/side chains will disrupt the zig-zag conformation and three
dimensional ‘packing’ of neighboring chains in their vicinity.
• Much of the LDPE material will form small crystallites, that can act as
physical crosslinks. This means that the bulk material will be a flexible
solid between Tg (Tg < -100° C; difficult to measure due to rapid
crystallization) and Tm (98 < Tm < 115° C).
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HOW DOES MOLECULAR
ARCHITECTURE AFFECT
PROPERTIES?
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LDPE properties
• Crystallites:
– Fewer defects means higher crystallinity
– Even single crystals are not 100% crystalline due to edges and corners,
and defects in the crystallite surfaces themselves.
– See Table 1, Appendix B, p. 614 for different polyethylenes
– Linear LDPE has ~ 80% crystallinity, Tm ~ 135 °C compared to LDPE
with 45-55% crystallinity, and a lower Tm.
• Performance:
– Excellent flexibility and easy processing
– Good structural strength
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Generalization
• Within one polymer family, it is possible to
infer differences in performance with changes
in constitution, configuration and
conformation.
• It is more difficult to compare across families
due to the influence of the different chemical
building blocs
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Constitutions
Configurations
Homopolymers
Copolymers
C, O, N are the most common elements in synthetic polymer chains
Table 2.1 – elements that form long chains
SYNTHETIC POLYMERS
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Synthetic polymers with the highest # of literature references.
This list is skewed toward thermoplastics. Thermosets and other matrix
materials have greater diversity in building blocks, and therefore have
fewer specific literature references.
TOP 100 POLYMERS
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TOP 100/GENERAL USE
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Top 100/general use
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Top 100/general use
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TOP 100/ENGINEERING PLASTICS
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Top 100/engineering plastics
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TOP 100/THERMOSETS
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Top 100/thermosets
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TOP 100/ELASTOMERS
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Top 100/elastomers
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TOP 100/ADHESIVES
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Top 100/adhesives
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TOP 100/SPECIALTY
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Top 100/specialty
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Top 100/specialty
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Top 100/specialty
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Medical application example
Citation data – one way to look for future trends
SciFinder Scholar
1985 - 2005
WHERE’S THE ‘ACTION’ IN
POLYMERS?
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Medical applications are a
rich applications area for
polymers.
Local variations in surface
roughness at the nanoscale
can induce strains in cell
membranes, leading to the
growth of F-actin stress
fibers that span the length
of the cell.
W.E. Thomas, D. E. Discher, V. P. Shastri,
Mechanical regulation of cells by materials
and tissues, MRS Bulletin, 35 (2010), 578583.
POLYMER SCIENCE DIRECTIONS
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Cells feel their environment
• Tissues are hydrated natural polymers with controlled
elasticity
• Most animals cells require adhesion to a solid to be
viable
• Tissue elasticity (~ kPa’s) is important for regulating cell
growth, maturation and differentiation. Brain – 0.2 < E <
1 kPa; fat – 2 < E < 4 kPa; muscle – 9 < E < 15 kPa;
cartilage – 20 < E < 25; bone – 30 < E < 40 kPa
• Nanoroughness seems to affect a number of cell
processes
• 3D scaffolding is important
• Mechanotransduction: cells adhere to surfaces via
adhesive proteins attached to adaptor proteins, to the
actomyosin cytoskeleton.
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There has been a major decline in publications on the physical properties
of polymers, dropping from ~23% in 1985-9 to ~13% over the last two
years. Plastics manufacturing, processing and fabrication has been
relatively steady, but may have declined recently. Information on
fundamental polymer chemistry seems to be nearly constant at 10% of
the total. Information about pharmaceutical applications is increasing
significantly, from 6% to ~12% recently.
TOPICS 1-5
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The synthetic high polymers category seems to be discontinued.
Coatings and inks seem to be fairly steady at 2 %. There is significant
growth in the areas of electric phenomena, optical, and radiation
technology. These three areas together constitute ~11% of the current
publication volume.
TOPICS 6-10
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There may be some renewed interest in the near term in photochemistry
applications. Synthetic elastomers show some fluctuations, as do textiles
and fibers. However, both surface chemistry + colloids, and biochemical
methods show significant growth.
TOPICS 11-15
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Ceramics applications seem to be decline, despite that fact the ceramers
are creating new interest. Cellulosics seems to be relatively steady, while
general biochemistry is growing. The textile topic is now combined with
fibers, and fossil fuel applications are dropping off dramatically.
TOPICS 16-20
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Semiconductor industry
Biomedical devices
POLYMERS FOR SPECIFIC
APPLICATION AREAS
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Semiconductor industry
•
•
•
•
•
•
•
•
PolyBenzImidazole
Polyimide
PolyAmide-Imide
PolyEtherImide
PolyEtherEtherKetone
Polyphenylene Sulfide
Polyvinylidene Fluoride
Ethylene-ChloroTriFluoroEthylene
• Ethylene-TetraFluoro-Ethylene
• Polyethylene Terephthalate
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• Polyfluorene derivatives
• Polymer transport layers:
– Polyanaline (PANI)
– Poly(3,4ethylenedioxythiophene)/Pol
y(styrenesulfonate) [PEDOTPSS]
• Polypyrrole
• Polythiophene
• Polydiacetylene
• Polyaryl ethers containing
Perfluorocyclobutyl (PFCB)
linkages; replacement for PMMA
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Biomedical applications
•
•
•
•
•
•
•
Polyanhydrides
Polyphosphazenes
Polyurethanes
Polyvinylchloride (PVC)
Polyethylene (PE)
Polypropylene (PP)
Polymethylmethacrylate
(PMMA)
• Polystyrene (PS)
• Polyester
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•
•
•
•
•
•
•
•
•
Polyamide
Polyacetal
Polysulfone
Polycarbonate
Polysiloxane
Polylactide (PLA)
Polyglycolide (PGA)
Poly(glycolide-co-lactide); PLGA
Poly(dioxanone)
Poly(carbonate)
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CARBON-CARBON BASED CHAINS
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Poly(acrylic acid). PAA_2.avi
Polyacrolein
Polyacrylamide
Polyacrylonitrile
Poly(methyl methacrylate)
Poly(2-hydroxyethyl methacrylate)
POLYACRYLICS
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Polyethylene
Chlorinated polyethylene
Polypropylene
Poly(1-butene)
Poly(isobutylene)
Polystyrene
Poly(2-vinyl pyridine)
POLY(OLEFINS)
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Poly(1,4-butadiene) BR (butadiene rubber)
Polyisoprene NR (natural rubber)
Polychloroprene CR, Neoprene
Polynorbornene
Poly(pentenamer) Ring-opening monomer
POLYDIENES
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Configurations for dienes
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Lower costs than ethylene-based polymers
Bond energies: C-F: 461 kJ/mol; C-H: 377 kJ/mol; C-Cl: 293 kJ/mol; C-Br:
251 kJ/mol; C-I: 188 kJ/mol
PTFE + copolymers with hexafluoropropylene, perfluoropropylvinylether
PTFCE
PVC
PVDF
PVDC
POLYHALOCARBONS
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Poly(vinyl acetate)- inexpensive emulsion systems (paints)
Poly(vinyl alcohol) - adhesives
Poly(vinyl formal) -adhesives
Poly(vinyl butyral) - adhesives
Poly(vinyl methyl ether) – adhesives, plasticizers
Poly(2-vinyl pyrrolidone) -
OTHER VINYL POLYMERS
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CARBON-NITROGEN CHAINS
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Perlons –[NH-CO-R]- ring-opening polymerizations
Nylons – [NH-R-NH-CO-R1-CO-]; Nylon x,y; Nomex, Kevlar
POLYAMIDES
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Poly(isocyanic acid), Nylon 1- [NH-CO-]; [CO-NR-CO-]
Kapton
POLYIMIDES
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Polyimines – [NH-CHR-]; polymerization of nitriles, hydrogenation;
poly(ethylene imine) is a flocculating aid
Poly(carbodiimides) – from isocyanates to give open cell rigid foams for
reaction injection molding
Polyurethane foams: diisocyanate + dialcohol to [-R-NH-CO-OR-]. Fibers,
films, paints, adhesives, foams, elastomers, image reproduction.
Polyureas: [-R-NH-CO-NH-]
POLYIMINES/POLYURETHANES
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Polyacetals: [-CHR-O]; engineering thermomplastics, low water
absorption, good wear resistance.
Polyethers [-R-O]. Poly(ethylene oxide) – water soluble packaging films,
surfactants. Poly(propylene oxide) – polyurethane intermediate,
lubricants, surfactants. Poly(tetrahydrofuran) – thermoplastic elastomers
and artifical leather.
Epoxies: based on epichlorihydrin. coatings, circuit boards, adhesives,
composites, road coatings.Bisphenol A is a major component.
PEEK: poly(ether ether ketone)
CARBON-OXYGEN CHAINS
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Phenolic resins
Polyesters:
aliphatic – lactones and self-condensed a- and w- hydroxy acids,
diols + dicarboxylic acids or chlorides,
aromatic – polycarbonates, poly(ethylene terephthalate), PBT,
crosslinked- phthalic anhydride + glycerol; alkyd paints (now mostly
replaced with latex paints)
CARBON-OXYGEN CHAINS
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Polysulfides: poly(phenylene sulfide) – Ryton, can be made to be
conductive by addiitives; poly(alkylene sulfide)s – Thiol Rubber
Polysulfones: oxidation of polysulfides, or polymerization via nucleophilic
substitution. Aromatic polysulfones have high use temperatures.
CARBON-SULFUR CHAINS
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Boron nitride – ‘parquet’ polymers, 2000 C.
Poly(siloxanes)-oils, elastomers, resins, inert.
Poly(dichlorophosphazene) – no uses; replace
chlorine with alkoxy, aryloxy or amino groups
INORGANIC POLYMERS
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GENERAL TYPES OF
CONSTITUTIONS AND
CONFIGURATIONS
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Both chain and step polymerizations yield linear homopolymers.
Vinyl polymers: head-to-head addition and head-to-tail addition
Tacticity: stereoregular arrangement of C-C backbone polymers
atactic – no regular repeating structure; amorphous, no Tm
syndiotactic – functional group is on alternate sides of the C-C chain; Tg
and Tm
isotactic – functional group is on the same side of the C-C chain; Tg and
Tm
Elastomers: cis and trans configurations. Tg and Tm
LINEAR HOMOPOLYMERS
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Comb, ladder, semiladder, star, dendrimer
IUPAC Compendium of Chemical Terminology, 2nd Ed., 1997.
NONLINEAR HOMOPOLYMERS
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‘dendron’ = tree (arborol;
cascade molecule)
Repeatedly branched
molecules; nearly spherical
Usually symmetric around a
core
www.wikipedia.com/dendrimer
DENDRIMERS
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Divergent: 1978- Vogtle, 1981 Denkewalter
(Allied Chemical), 1983, Tomalia (Dow
Chemical); 1985, Newkome
Convergent: 1990, Frechet
SYNTHESIS
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Low molecular weight: dendrimers, dendrons
High molecular weight: dendronized polymers, hyperbranched polymers,
Polymer brush
Dendrimer functionalization: mimics the site of biological molecules
Add water solubility by using hydrophilic groups for the outermost layer
Control of: toxicity, chirality, crystallinity,
TYPES
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Convergent – three addition cycles; 3rd generation dendrimer
Each generation increases the size by 2
GENERATIONS
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0 generation: ethylene diamine + methyl acrylate + ethylene diamine
Low generations: flexible molecules with no inner regions
G3 to G4: internal space separate from outer shell
G7: solid-like particles with dense surfaces
Multiple steps mean that synthesis is difficult
EXAMPLE-POLY(AMIDOAMINE)
PAMAM
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Multifunctional core
Each step must be driven to completion to ensure symmetry
DIVERGENT SYNTHESIS
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Small molecules end up on the sphere surface
CONVERGENT SYNTHESIS
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Encapsulation of hydrophobic
compounds and anticancer drugs
Monodisperse, hydrophilicity,
variable functionality
Covalent links; ionic bonds,
encapsulation
DRUG DELIVERY
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Network: phenolformaldehyde
resin
IPN: two crosslinked
polymers not bonded to
each other
Semi-interpenetrating
polymer network:
crosslinked epoxy with
vinyl polymer
Long sequences: block, graft, star, blend,…
Networks: crosslinked, interpentrating, co-terminous
COPOLYMERS
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CONFORMATIONS
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0 
k  Mw
R 
2 3/2
0

k1  M w
M w 
3/2
1

Mw
R0 = end-to-end distance; proportional to the
square root of molecular weight

Coil shapes are dynamic
The most probable shape is bean-like: oblate ellipsoid (3 unequal axes;
1.36/0.78/0.50)
Least probable shapes are spherical, rod-like
RANDOM COIL CONFORMATION
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Human serum albumin conformation.
www.wikipedia.org
Shape changes with pH, T, salts, ionic strength,
ion types.
Chain assumes a minimum conformation in solution; beyond this T, the
polymer precipitates
Good solvent: polymer expands beyond the random coil conformation
Globular proteins have conformation similar to random coils.
THETA SOLVENT
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Extended chain – repulsive groups
Random coil – interactions between
chain/chain and chain/solvent units
are similar
Folded chain – zig-zag conformation
for C-C backbone systems
Helix – nylons, PP
CRYSTALLINE, LINEAR POLYMERS
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Isotactic, syndiotactic C-C backbone chains: polypropylene
Unsubstituted linear addition polymers: polyoxymethylene
Addition polymers with di-substituted vinyl groups: poly(vinylidene
dichloride)
Straight chain condensation polymers: PET
Symmetric ring-containing condensation polymers: poly(phenylene
terephthalamide)
Some nonstereoregular asymmetric polymers: poly(vinyl alcohol)
Helix: bulky side groups, low energy conformation
WHICH POLYMERS CRYSTALLIZE?
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Polyacrylonitrile; polystyrene; polybutadiene
Crystalline; amorphous; elastomer
TERPOLYMER SYSTEM
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MIXTURES, COPOLYMERS
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