Chapter 4- Polymer Structures
Chapter 4- Polymer Structures
ISSUES TO ADDRESS...
What are the basic
• Classification?
• Monomers and chemical groups?
• Nomenclature?
• Polymerization methods?
• Molecular Weight and Degree of Polymerization?
• Molecular Structures?
• Crystallinity?
• Microstructural features?
TEM of spherulite structure in natural rubber(x30,000).
• Chain-folded lamellar crystallites (white lines) ~10nm thick extend radially.
MatSE 280: Introduction to Engineering Materials
©D.D. Johnson 2004, 2006, 2007-08
MatSE 280: Introduction to Engineering Materials
Polymer Microstructure
©D.D. Johnson 2004, 2006, 2007-08
Polymer Microstructure
• Polymer = many mers
• Covalent chain configurations and strength:
More rigid
Van der Waals, H
Adapted from Fig. 14.2, Callister 6e.
Polyethylene perspective of molecule
Direction of increasing strength
Adapted from Fig. 14.7, Callister 6e.
A zig-zag backbone structure with covalent bonds
MatSE 280: Introduction to Engineering Materials
©D.D. Johnson 2004, 2006, 2007-08
MatSE 280: Introduction to Engineering Materials
©D.D. Johnson 2004, 2006, 2007-08
1
Common Examples
Common Classification
- Textile fibers: polyester, nylon…
• Thermoplastics: polymers that flow more easily when
squeezed, pushed, stretched, etc. by a load (usually at
elevated T).
- IC packaging materials.
– Can be reheated to change shape.
- Resists for photolithography/microfabrication.
• Thermosets: polymers that flow and can be molded
initially but their shape becomes set upon curing.
- Plastic bottles (polyethylene plastics).
– Reheating will result in irreversible change or decomposition.
- Adhesives and epoxy.
• Other ways to classify polymers.
– By chemical functionality (e.g. polyacrylates, polyamides,
polyethers, polyeurethanes…).
– Vinyl vs. non-vinyl polymers.
– By polymerization methods (radical, anionic, cationic…).
– Etc…
- High-strength/light-weight fibers: polyamides,
polyurethanes, Kevlar…
- Biopolymers: DNA, proteins, cellulose…
MatSE 280: Introduction to Engineering Materials
MatSE 280: Introduction to Engineering Materials
©D.D. Johnson 2004, 2006, 2007-08
Common Chemical Functional Groups
H
Ethylene
(ethene)
Methyl alcohols
C C
H
H
H
Propylene
(propene)
Common Hydrocarbon Monomers
Alcohols
H
©D.D. Johnson 2004, 2006, 2007-08
H
=
C C
H
H
Ethers
Dimethyl Ether
Acids
Acetic acid
C H
H
1-butene
2-butene
trans
cis
Aldehydes
Acetylene
(ethyne)
Saturated hydrocarbons
(loose H to add atoms)
MatSE 280: Introduction to Engineering Materials
Unsaturated hydrocarbons
(double and triple bonds)
©D.D. Johnson 2004, 2006, 2007-08
Formaldehyde
H C C H
Aromatic
hydrocarbons
MatSE 280: Introduction to Engineering Materials
Phenol
©D.D. Johnson 2004, 2006, 2007-08
2
Nomenclature
Some Common Polymers
Monomer-based naming:
poly________
Common backbone with substitutions
Polyacrylonitrile (PAN)
H
H
C
C
H
C
Monomer name goes here
e.g. ethylene -> polyethylene
N
Vinyl polymers (one or more H’s of ethylene can be substituted)
H
H
C C
H
X
H
H
C
C
H
X
if monomer name contains more than one word:
poly(_____ ____)
Monomer name in parentheses
e.g. acrylic acid -> poly(acrylic acid)
Note: this may lead to polymers with different names but same structure.
H H H H
…
C C C C
H H H H
…
…
H H H H
polyethylene
MatSE 280: Introduction to Engineering Materials
polymethylene
MatSE 280: Introduction to Engineering Materials
©D.D. Johnson 2004, 2006, 2007-08
Polymerization Methods
…
C C C C
H H H H
©D.D. Johnson 2004, 2006, 2007-08
Polymerization Methods
A. Free Radical Polymerization
A. Free Radical Polymerization
1. Initiation
H
R
H
R
C C
Free radical initiator
(unpaired electron)
H
H
2. Propagation
H
H
H
C
C
H
monomer
Radical
transferred
R
H
H
C
C
H
H
H
H
H
R
C C
H
H
H
C C
H
H
H
H
C
C
C
C
H
H
H
H
H
H
R
H
H
H
H
H
H
C
C
C
C
C
C
H
H
H
H
H
H
H
R
H
C
R
H
C
sp2 carbons
C
C
H
H
σ bonds
π bond
MatSE 280: Introduction to Engineering Materials
H
H
sp3 carbon
©D.D. Johnson 2004, 2006, 2007-08
H
R
H
H
C
H
H
C
H
H
H
C
C
Both carbon atoms will
change from sp 2 to sp 3.
H
MatSE 280: Introduction to Engineering Materials
©D.D. Johnson 2004, 2006, 2007-08
3
Polymerization Methods
Polymerization Methods
Loses water
(condensation)
B. Stepwise polymerization
A. Free Radical Polymerization
3. Termination
O
H2N
R
H
H
C
C
H
H
+
R
R
H
H
C
C R
H
H
R
C
O
O
+
H2N
OH
R
C
H2N
OH
R
C
N
H
R
C
OH
+
Proteins (polypeptides have similar composition)
R
H
H
C
C
H
H
+
R
H
H
C
C
H
H
R
H
H
H
H
C
C
C
C
H
H
H
H
O
H
N H C
C
R
R
Various R groups…
∑N j M j
O
H
€
j
∑N j M j =
Total # of polymer chains
j
∑ N j M€2j
∑W j M j
Mw =
j
∑W j
=
j
20 + 16 + 10
M monomer = 15.3M monomer
3
∑N j =
Total weight
Weight average
€ molecular weight:
€
10 mers
Mj = jmo
mass of polymer chain with length j
(mo = monomer molecular weight).
∑N j
j
16 mers
Nj = # of polymer chains with length j
j
=
∑N j
j
©D.D. Johnson 2004, 2006, 2007-08
H
n
©D.D. Johnson 2004, 2006, 2007-08
mo ∑ N j j
j
Mn =
Note:
MatSE 280: Introduction to Engineering Materials
+ (n-1)
C
Number average molecular weight:
Not only are there different structures (molecular arrangements)
…… but there can also be a distribution of molecular weights
(i.e. number of monomers per polymer molecule).
This is what is called number average molecular weight.
O
R
n
MatSE 280: Introduction to Engineering Materials
Molecular Weights
Average molecular weight =
H
N
Anionic polymerization, cationic
polymerization, coordination
polymerization…
©D.D. Johnson 2004, 2006, 2007-08
20 mers
H
C. Other methods
Intentional or unintentional molecules/impurities can also terminate.
MatSE 280: Introduction to Engineering Materials
O
H
O
In general:
€
j
W j = N jM j
∑N j M j
j
+1
∑ N j M αj €
M=
j
∑ N j M αj
If α = 0 then
Mn
If α = 1 then Mw
j
MatSE 280: Introduction to Engineering Materials
€©D.D. Johnson 2004, 2006, 2007-08 €
€
4
Molecular Weights
Molecular Weight: Different Notations
In Callister Textbook
In Lecture Notes
Mn = ∑ x i Mi
∑N j M j
Mn =
j
i
∑N j
Ni
xi =
∑N j
j
∑ N j M 2j
€
Mw =
j
€
j
∑N j M j
Why do we care about weight average MW?
-some properties are dependent on MW (larger MW polymer chains can
contribute to overall properties more than smaller ones).
Ni M i
wi =
∑N j M j
j
Mw = ∑w i Mi
€
€
j
MatSE 280: Introduction to Engineering Materials
Distribution of
polymer weights
i
©D.D. Johnson 2004, 2006, 2007-08
Examples –
Light scattering: larger molecules scatter more light than smaller ones.
Infrared absorption properties: larger molecules have more side
groups and light absorption (due to vibrational modes of side groups)
varies linearly with number of side groups.
MatSE 280: Introduction to Engineering Materials
©D.D. Johnson 2004, 2006, 2007-08
€
€
Example 1
Polydispersity and Degree of Polymerization
Polydispersity:
Mw
≥1
Mn
Compute the number-average degree of polymerization for polypropylene,
given that the number-average molecular weight is 1,000,000 g/mol.
When polydispersity = 1, system is monodisperse.
€
Degree of Polymerization:
Mer molecular weight of PP is
Number avg degree of polymerization
Weight avg degree of polymerization
€
MatSE 280: Introduction to Engineering Materials
€
C3H6
What is “mer” of PP?
nn =
Mn
mo
M
nw = w
mo
©D.D. Johnson 2004, 2006, 2007-08
mo=3AC+6AH
=3(12.01 g/mol)+6(1.008 g/mol)
= 42.08 g/mol
Number avg degree of polymerization
nn =
Mn
106 g / mol
=
= 23,700
mo 42.08g / mol
MatSE 280: Introduction to Engineering Materials
©D.D. Johnson 2004, 2006, 2007-08
€
5
Example 2 (a, b, and c)
Example 2 (cont.)
A. Calculate the number and weight average degrees of polymerization
and polydispersity for a polymer sample with the following distribution.
Avg # of monomers/chain
10
100
500
1000
5000
50,000
nn =
=
j
j
=
j
j
∑ jN
∑N
j
j
Relative abundance
5
25
50
30
10
5
Mw if monomer is methylmethacrylate (5C, 2O, and 8H)
So m 0= 5(12)+2(16)+8(1)= 100 g/mol
j
2
o
j
j
j
Polydispersity:
2
∑ ( jm ) N ∑ j N
=
∑ N ( jm ) ∑ jN
j
j
o
j
j
Note: m 0 cancels in all these!
j
©D.D. Johnson 2004, 2006, 2007-08
€
MatSE 280: Introduction to Engineering Materials
Example 2 (cont.)
C. If we add polymer chains with avg # of monomers = 10 such that their
relative abundance changes from 5 to 10, what are the new number
and weight average degrees of polymerization and polydispersity?
nn =
Mn
=
mo
=
nw =
∑ jN
∑N
j
j
j
Mw 3,580,000
=
~ 12.52
Mn
286,040
€
5 *10 2 + 25 *100 2 + 50 * 500 2 + 30 *1000 2 + 10 * 5000 2 + 5 * 50000 2
=
= 35, 800
5 *10 + 25 *100 + 50 * 500 + 30 *1000 + 10 * 5000 + 5 * 50000
MatSE 280: Introduction to Engineering Materials
©D.D. Johnson 2004, 2006, 2007-08
Sequence isomerism
For an asymmetric monomer
T
Add 5 more monomers of length 10 ….
H
+
T
H
j
10 * 10 + 25 * 100 + 50 * 500 + 30 * 1000 + 10 * 5000 + 5 * 50000
= 2750
10 + 25 + 50 + 30 + 10 + 5
e.g. poly(vinyl fluoride):
2
Mw ∑ j j N j
=
= 35,800
mo
∑ j jN j
Note: significant change in number average (3.8 %)
but no change in weight average!
M w 3, 580, 000
=
~ 13
Mn
275000
MatSE 280: Introduction to Engineering Materials
©D.D. Johnson 2004, 2006, 2007-08
H
T
H
T
H
H
T
H
T
T
H
e.g. PMMA
F
H
H
F
H
H
H
C
C
C
C C
C
C
C
H
H3C H3C
H3C
O O
O O O O
O
C H C H C H C
H
H
H
F H
H
H
F
C
C
C
C C
C
H
CH3 H
CH3H
CH3 H
T to T
H to H
Polydispersity:
T
H
H to T
€
CH3
|
-CH2-C|
CO2CH3
Mn = nnmo = 2860.4(100g / mol ) = 286,040g / mol
Mw = nw mo = 35,800(100g / mol ) = 3,580,000g / mol
j
5 *10 + 25 *100 + 50 * 500 + 30 *1000 + 10 * 5000 + 5 * 50000
= 2860.4
5 + 25 + 50 + 30 + 10 + 5
Mw
1
=
mo mo
nw =
∑ jN
∑N
M n m0
=
mo m0
B. If the polymer is PMMA, calculate number and weight average
molecular weights.
Random arrangement
MatSE 280: Introduction to Engineering Materials
H3C
O
H to T
H to T
C
C
CH3
H to T
Exclusive H to T arrangement (Why?)
©D.D. Johnson 2004, 2006, 2007-08
6
Polymer Molecular Configurations
• Regularity and symmetry of side groups affect properties
Polymer Geometrical Isomerism
• Regularity and symmetry of side groups affect properties
Can it crystallize?
Melting T?
Polymerize
H
H
• Stereoisomerism: (can add geometric isomerism too)
Syndiotactic
Alternating sides
Atactic
Randomly placed
- Conversion from one stereoisomerism to another is not possible by simple
rotation about single chain bond; bonds must be severed first, then reformed!
-Conversion from one isomerism to another is not possible by simple
rotation about chain bond because double-bond is too rigid!
-See Figure 4.8 for taxonomy of polymer structures
MatSE 280: Introduction to Engineering Materials
©D.D. Johnson 2004, 2006, 2007-08
Polymer Structural Isomerism
2
1
H2C
C
C
H
• Covalent chain configurations and strength:
4
CH3
©D.D. Johnson 2004, 2006, 2007-08
Polymer Microstructure
Some polymers contain monomers with more than 1 reactive site
e.g. isoprene
trans-structure
with R= CH3 to form rubber
Cis-polyisoprene
trans-polyisoprene
Isotactic
On one side
MatSE 280: Introduction to Engineering Materials
cis-structure
More rigid
Van der Waals, H
CH2
3
trans-isoprene
Direction of increasing strength
trans-1,4-polyisoprene
CH3
C
H2
C
C
H
trans-1,2-polyisoprene
H2
C
H2
C
n
H2
C H
C
n
C
H3C
Adapted from Fig. 14.7, Callister 6e.
3,4-polyisoprene
CH
H2C
C
H2C
Short branching
n
CH3
Long branching
Note: there are also cis-1,4- and cis-1,2-polyisoprene
MatSE 280: Introduction to Engineering Materials
©D.D. Johnson 2004, 2006, 2007-08
MatSE 280: Introduction to Engineering Materials
Star branching
Dendrimers
©D.D. Johnson 2004, 2006, 2007-08
7
CoPolymers
Molecular Structure
• Random, Alternating, Blocked, and Grafted
How do crosslinking and branching occur in polymerization?
1. Start with or add in monomers that have more than 2 sites that bond
with other monomers, e.g. crosslinking polystyrene with divinyl benzene
• Synthetic rubbers are often copolymers.
…
e.g., automobile tires (SBR)
stryene
…
polystyrene
Styrene-Butadiene Rubber random polymer
…
Control degree of
+
crosslinking by
styrene-divinyl
styrene
benzene ratio
divinyl benzene
…
crosslinked polystyrene
Monomers with trifunctional groups lead to network polymers.
MatSE 280: Introduction to Engineering Materials
MatSE 280: Introduction to Engineering Materials
©D.D. Johnson 2004, 2006, 2007-08
Molecular Structure
Example 3
Nitrile rubber copolymer, co-poly(acrylonitrile-butadiene), has
Branching in polyethylene (back-biting)
H2C CH2
R
H2
C
C
H2
H2
C
Same as
C
H2
H2
C
Mn = 106,740g / mol
C H
H
R
CH2
Radical moves to a different carbon
C
CH2
(H transfer)
C
H H2
€
H
H
H
nn = 2000
Calculate the ratio of (# of acrylonitrile) to (# of butadiene).
H
H
C
©D.D. Johnson 2004, 2006, 2007-08
C
H
CH2
C
R
C
H H2
3 C = 3 x 12.01 g/mol
3 H = 3 x 1.008 g/mol
1 N = 1 x 14.007 g/mol
€
4 C = 4 x 12.01 g/mol
6 H = 6 x 1.008 g/mol
m 0= 54.09 g/mol
m 0= 53.06 g/mol
CH2
1,4-addition product
We need to use an
avg. monomer MW:
Polymerization continues from this carbon
mo =
Mn 106,740
=
= 53.57g / mol
nn
2000
mo = f1m 1 + f2m 2 = f1(m 1 − m 2 ) + m 2
Process is difficult to avoid and leads to (highly branched) low-density PE .
When there is small degree of branching you get high-density PE.
MatSE 280: Introduction to Engineering Materials
f1 =
€
m 0 − m 2 53.37 − 54.09
=
= 0.7
€ − 54.09
m 1 − m 2 53.06
MatSE 280: Introduction to Engineering Materials
©D.D. Johnson 2004, 2006, 2007-08
€
€
f2 = 1− f1 = 0.3
f2 0.7
=
→7 :3
f1 0.3
©D.D. Johnson 2004, 2006, 2007-08
€
8
Vulcanization
Molecular Weight and Crystallinity
See also sect. in Chpt. 8
• Crosslinking in elastomers is called vulcanization, and is achieved by
irreversible chemical reaction, usually requiring high temperatures.
• Molecular weight, Mw: Mass of a mole of chains.
• Sulfur compounds are added to form chains that bond adjacent
polymer backbone chains and crosslinks them.
• Unvulcnaized rubber is soft and tacky an poorly resistant to wear.
• Tensile strength (TS):
e.g., cis-isoprene
Single bonds
--often increases with M w.
--Why? Longer chains are entangled (anchored) better.
Stress-strain curves
• % Crystallinity: % of material that is crystalline.
Double bonds
+ (m+n) S
--TS and E often increase
with % crystallinity.
--Annealing causes
crystalline regions to grow.
% crystallinity increases.
(S)m
(S)n
crystalline
region
amorphous
region
Adapted from Fig. 14.11, Callister 6e.
MatSE 280: Introduction to Engineering Materials
MatSE 280: Introduction to Engineering Materials
©D.D. Johnson 2004, 2006, 2007-08
Polymer Crystallinity
polyethylene
Volume fraction of crystalline component.
• Some are amorphous.
• Some are partially crystalline (semi-crystalline).
• Why is it difficult to have a 100% crystalline polymer?
%crystallinity =
ρc ( ρ s − ρa )
× 100%
ρ s ( ρc − ρa )
ρs = density of specimen in question
ρa = density of totally amorphous polymer
ρc = density of totally crystalline polymer
%crystallinity =
€
Mcrystalline
Mtotal
ρ V
ρ
× 100% = c c × 100% = c fc × 100%
ρsVs
ρs
Mtotal = Mcrystalline + Mamophous
©D.D. Johnson 2004, 2006, 2007-08
Using definition of volume fractions:
Ms = Mc + Ma
ρsVs = ρcVc + ρaVa
V
V
ρs = ρc c + ρa a
Vs
Vs
V
fc = c
Vs
V
fa = a
Vs
= ρc fc + ρa fa = ρc fc + ρa (1− fc ) = fc ( ρc − ρa ) + ρa
€
€
ρ − ρa
fc = s
ρc − ρa
€
Substituting in f c into the original definition:
MatSE 280: Introduction to Engineering Materials
©D.D. Johnson 2004, 2006, 2007-08
MatSE 280: Introduction to Engineering Materials
ρ ( ρ − ρa )
%crystallinity = c s
× 100%
ρ s ( ρc − ρa )
€
©D.D. Johnson 2004, 2006, 2007-08
9
Polymer Crystallinity
Degree of crystallinity depends on processing conditions (e.g.
cooling rate) and chain configuration.
Semi-Crystalline Polymers
Fringed micelle model: crystalline region embedded in amorphous region.
A single chain of polymer may pass through several crystalline regions as
well as intervening amorphous regions.
Cooling rate: during crystallization upon cooling through MP,
polymers become highly viscous. Requires sufficient time for
random & entangled chains to become ordered in viscous liquid.
Chemical groups and chain configuration:
More Crystalline
Less Crystalline
Smaller/simper side groups
Larger/complex side groups
Linear
ρ − ρa
fc = s
ρc − ρa
Highly branched
Crystalline volume fractions Important
Crosslinked, network
Isotactic or syndiotactic
Random
MatSE 280: Introduction to Engineering Materials
©D.D. Johnson 2004, 2006, 2007-08
Semi-Crystalline Polymers
Chain-folded model: regularly shaped platelets (~10 – 20 nm thick)
sometimes forming multilayers.
Average chain length
€
MatSE 280: Introduction to Engineering Materials
©D.D. Johnson 2004, 2006, 2007-08
Semi-Crystalline Polymers
Spherulites: Spherical shape composed of aggregates of chain-folded crystallites.
>> platelet thickness.
Natural rubber
Cross-polarized light through
spherulite structure of PE.
MatSE 280: Introduction to Engineering Materials
©D.D. Johnson 2004, 2006, 2007-08
MatSE 280: Introduction to Engineering Materials
©D.D. Johnson 2004, 2006, 2007-08
10
Diblock copolymers
Thermoplastics vs Thermosets
• Thermoplastics:
T
--little cross linking
--ductile
--soften w/heating
--polyethylene (#2)
polypropylene (#5)
polycarbonate
polystyrene (#6)
Representative polymer-polymer
phase behavior with different
architectures:
MatSE 280: Introduction to Engineering Materials
Molecular weight
MatSE 280: Introduction to Engineering Materials
©D.D. Johnson 2004, 2006, 2007-08
What Are Expected Properties?
• Packing of “spherical” atoms as in ionic and metallic crystals led to
crystalline structures.
• Would you expect melting of nylon 6,6 to be lower than PE ?
O H 
O
H 
 
||  | 
||
|
 
− N − C  − N −C − C  − N −C −
 
 
| |
|
|
|
H  H
H H  6 H
4
H H
−C− C−
H H
nylon 6,6
• How polymers pack depend on many factors:
• long or short, e.g. long (-CH 2-)n.
• stiff or flexible, e.g. bendy C-C sp 3.
• smooth or lumpy, e.g., HDPE.
• regular or random
• single or branched
• slippery or sticky, e.g. C-H covalent (nonpolar) joined via vdW.
+
+
+
O H 
O
H 
 
||  | 
||
|
 
 
− N − C  − N −C − C  − N −C −
 
 
| |
|
|
|
H  H
H H  6 H
4
€
a)
b)
+
polyethylene
+
+ bonds
+ Waals
Van der
+
+
+
Hydrogen
bonds
€
Analogy: Consider dried (uncooked) spaghetti (crystalline) vs.
cooked and buttered spaghetti (amorphous).
• pile of long “stiff” spaghetti forms a random arrangement.
• cut into short pieces and they align easily.
©D.D. Johnson 2004, 2006, 2007-08
Tg
Tg: from rubbery to rigid as T lowers
Packing of Polymers
MatSE 280: Introduction to Engineering Materials
Tm
--large cross linking (10 to 50% of mers) Adapted from Fig. 15.18, Callister 6e.
--hard and brittle
Tm: melting over wide range of T
--do NOT soften w/heating
depends upon history of sample
--vulcanized rubber, epoxies,
consequence of lamellar structure
thicker lamellae, higher T m.
polyester resin, phenolic resin
©D.D. Johnson 2004, 2006, 2007-08
Candle wax more crystalline than PE, even though same
chemical nature.
Callister,
rubber
Fig. 16.9
tough
plastic
partially
crystalline
solid
crystalline
solid
• Thermosets:
A) Phase separation with mixed
LINEAR homopolymers.
B) Mixed LINEAR homopolymers and
DIBLOCK copolymer gives
surfactant-like stabilized state.
C) Covalent bond between blocks in
DIBLOCK copolymer give
microphase segregation.
F. Bates, Science 1991.
viscous
liquid
mobile
liquid
€
+
+
H
H
−C− C−
H H
€ cohesion in Nylon vs PE?
What is the source of intermolecular
How does the source of linking affect temperature?
With H-bonds vs vdW bonds, nylon is expected to have (and does) higher melting T.
MatSE 280: Introduction to Engineering Materials
©D.D. Johnson 2004, 2006, 2007-08
11
What Are Expected Properties?
What Are Expected Properties?
Which polymer more likely to crystallize? Can it be decided?
Which polymer more likely to crystallize? Can it be decided?
Linear syndiotactic polyvinyl chloride
Networked
Phenol-Formaldehyde
(Bakelite)
Linear isotactic polystyrene
Linear and highly crosslink
cis-isoprene
+
H
+ H 20
• For linear polymers, crystallization is more easily accomplished as
chain alignment is not prevented.
• Crystallization is not favored for polymers that are composed of
chemically complex mer structures, e.g. polyisoprene .
• Linear and syndiotactic polyvinyl chloride is more likely to crystallize.
• The phenyl side-group for PS is bulkier than the Cl side-group for PVC.
• Generally, syndiotactic and isotactic isomers are equally likely to crystallize.
MatSE 280: Introduction to Engineering Materials
©D.D. Johnson 2004, 2006, 2007-08
What Are Expected Properties?
Which polymer more likely to crystallize? Can it be decided?
alternating
Poly(Polystyrene-Ethylene)
Copolymer
• Networked and highly crosslinked structures are near impossible
to reorient to favorable alignment.
• Not possible to decide which might crystallize. Both not likely to do so.
MatSE 280: Introduction to Engineering Materials
©D.D. Johnson 2004, 2006, 2007-08
Detergents
• Soap is a detergent based on animal or vegetable product,
some contain petrochemicals
water
random
poly(vinyl chloride-tetra-fluoroethylne)
copolymer
detergent
grease
• What properties of soap molecules do you need to remove grease?
• “green” end must be “hydrophilic”. Why?
• Opposite end must be hydrocarbon. Why?
• Alternating co-polymer more likely to crystallize than random ones, as they
are always more easily crystallized as the chains can align more easily.
MatSE 280: Introduction to Engineering Materials
©D.D. Johnson 2004, 2006, 2007-08
Water must be like oxygen (hoard
electrons and promote H-bonding)
e.g., oxy-clean®
MatSE 280: Introduction to Engineering Materials
grease
©D.D. Johnson 2004, 2006, 2007-08
12
Simple polymer: Elmers glue + Borax  SLIME!
Chemistry
Elmer’s glue is similar to “poly (vinyl alcohol)” with formula:
OH
OH
OH
OH
OH
OH
OH
OH
OH
OH
OH
OH
OH
OH
OH
this is a SHORT, n=15 chain of poly(vinyl alcohol)
Simple polymer: Elmer’s glue + Borax  SLIME!
Hydrolyzed molecule acts in a condensation reaction with PVA,
crosslinking it.
B(OH) 3 + 2H 2O  B(OH) 4- + H 3O+ pH=9.2

Borax is sodium tetraborate decahydrate (B4Na 2O7 • 10 H 2O).
The borax actually dissolves to form boric acid, B(OH) 3.
This boric acid-borate solution is a buffer with a pH of about 9 (basic).
Boric acid will accept a hydroxide OH- from water.
B(OH) 3 + 2H 2O  B(OH) 4- + H 3O+ pH=9.2

Hydrolyzed molecule acts in a condensation reaction
with PVA, crosslinking it.
MatSE 280: Introduction to Engineering Materials
Crosslinked
©D.D. Johnson 2004, 2006, 2007-08
Range of Bonding and Elastic Properties
Crosslinking ties chains via weak non-covalent
(hydrogen) bonds, so it flows slowly.
MatSE 280: Introduction to Engineering Materials
©D.D. Johnson 2004, 2006, 2007-08
Summary
• Polymers are part crystalline and part amorphous.
Is “slime” a thermoset or thermoplastic, or neither?
Thermoset
bonding
• Covalent bonds
form crosslinks
Slime?
• H-bonds form
crosslinks
Thermoplastic
bonding
• Induced dipolar bonds
form crosslinks
Stiffness increases
• The more crosslinking the stiffer the polymer. And,
networked polymers are like heavily crosslinked ones.
• Many long-chained polymers crystallize with a Spherulite
microstructure - radial crystallites separated by
amorphous regions.
• Optical properties: crystalline -> scatter light (Bragg)
amorphous -> transparent.
Most covalent molecules absorb light outside visible spectrum ,
e.g. PMMA (lucite) is a high clarity tranparent materials.
Where is nylon?
MatSE 280: Introduction to Engineering Materials
• The more “lumpy” and branched the polymer, the less
dense and less crystalline.
©D.D. Johnson 2004, 2006, 2007-08
MatSE 280: Introduction to Engineering Materials
©D.D. Johnson 2004, 2006, 2007-08
13