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1. 1
Video Lectures for MBA
By:
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2. 2
"I just want to say one word to
you -- just one word -- 'plastics.'"
Advice to Dustin Hoffman's
character in The Graduate
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3. 3
Polymers: Introduction
• Polymer: High molecular weight molecule made
up of a small repeat unit (monomer).
– A-A-A-A-A-A-A-A-A-A-A-A-A-A-A-A-A-A-A-A-A-A-A-A
• Monomer: Low molecular weight compound that
can be connected together to give a poymer
• Oligomer: Short polymer chain
• Copolymer: polymer made up of 2 or more
monomers
– Random copolymer: A-B-B-A-A-B-A-B-A-B-B-B-A-A-B
– Alternating copolymer: A-B-A-B-A-B-A-B-A-B-A-B-A-B
– Block copolymer: A-A-A-A-A-A-A-A-B-B-B-B-B-B-B-B
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4. 4
Types of Polymers
• Polymer Classifications
– Thermoset: cross-linked polymer that cannot be
melted (tires, rubber bands)
– Thermoplastic: Meltable plastic
– Elastomers: Polymers that stretch and then return to
their original form: often thermoset polymers
– Thermoplastic elastomers: Elastic polymers that can
be melted (soles of tennis shoes)
• Polymer Families
– Polyolefins: made from olefin (alkene) monomers
– Polyesters, Amides, Urethanes, etc.: monomers linked
by ester, amide, urethane or other functional groups
– Natural Polymers: Polysaccharides, DNA, proteinsVideo.edhole.com

5. 5
Common Polyolefins
Monomer Polymer
Ethylene
H3C
CH3
n
Repeat unitPolyethylene
CH3
CH3
n
CH3 CH3 CH3 CH3 CH3 CH3CH3
Propylene
Polypropylene
Ph
CH3
n
Ph Ph Ph Ph Ph PhPh
Styrene
Polystyrene
Cl
CH3
n
Cl Cl Cl Cl Cl ClCl
Vinyl Chloride
Poly(vinyl chloride)
F2C CF2
Tetrafluoroethylene
F3C
F2
C
C
F2
F2
C
C
F2
F2
C
C
F2
F2
C
C
F2
F2
C
C
F2
F2
C
C
F2
CF3
n
Poly(tetrafluoroethylene): Teflon
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6. 6
Polyesters, Amides, and Urethanes
Monomer Polymer
CO2HHO2C
HO
OH
O O
HO O
H2
C
H2
C O
n
Terephthalic
acid
Ethylene
glycol
Poly(ethylene terephthalate
H
Ester
HO OH
O O
4
H2N NH24
Adipic Acid 1,6-Diaminohexane Nylon 6,6
HO N
H
N
H
H
O O
4 4
n
CO2HHO2C
Terephthalic
acid
NH2H2N
1,4-Diamino
benzene
Kevlar
O
HO
O
H
N
H
N H
n
Amide
HO
OH
Ethylene
glycol
H2
COCN NCO
4,4-diisocyantophenylmethane
Spandex
H2
C
H
N
H
N
O
HO
O
O
H2
C
H2
C O H
n
Urethane linkage
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7. 7
Natural Polymers
Monomer Polymer
Isoprene
n
Polyisoprene:
Natural rubber
O
H
HO
H
HO
H
H
OHH
OH
OH
Poly(ß-D-glycoside):
cellulose
O
H
O
H
HO
H
H
OHH
OH
OH
H
n
ß-D-glucose
H3N
O
O
R
Polyaminoacid:
protein
H3N
O
H
N
R1
O
H
N
Rn+1
O
OH
Rn+2n
AminoAcid
Base
O
OH
OP
O
O
O
oligonucleic acid
DNA
Nucleotide
Base = C, G, T, A
Base
O
O
OP
O
O
O
DNA
DNA
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8. 8
What Makes Polymers Unique?
• Really big molecules (macromolecules) like
polymers have very different properties than small
molecules
– Chain entanglement: Long
polymer chains get entangled with
each other.
• When the polymer is melted, the
chains can flow past each other.
• Below the melting point, the chains
can move, but only slowly. Thus the
plastic is flexible, but cannot be easily
stretched.
• Below the glass transition point, the
chains become locked and the
polymer is rigid
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9. 9
Physical Properties
Stretch
Linear Polymer
The chains can be stretched, which causes
them to flow past each other. When released,
the polymer will not return to its original form.
Stretch
Cross-Linked Polymer
The cross-links hold the chains together.
When released, the polymer will return to it's
original form.
Relax
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10. 10
Polymer Synthesis
• There are two major classes of polymer formation
mechanisms
– Addition polymerization: The polymer grows by
sequential addition of monomers to a reactive site
• Chain growth is linear
• Maximum molecular weight is obtained early in the reaction
– Step-Growth polymerization: Monomers react together
to make small oligomers. Small oligomers make
bigger ones, and big oligomers react to give polymers.
• Chain growth is exponential
• Maximum molecular weight is obtained late in the reaction
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11. 11
Addition Polymerization
In*
A
Initiation
In A* A
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12. 12
Addition Polymerization
Propagation
In*
A
Initiation
In A A* A
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13. 13
Addition Polymerization
Propagation
AIn*
A
Initiation
In A A A*
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14. 14
Addition Polymerization
Propagation
nA
In A A A A
n
A*
A A A A A
m
In A A A A
n
A
*A A A A A
m
Combination
*A A A A A
m
In A A A A
n
A
B A A A A
m
Disproportionation
Termination
Reactive site is consumed
A
In A A A A
n
A
A*
Chain Transfer
New reactive site
is produced
MW∝
kpropagation
ktermination
MW
% conversion
0 100
In*
A
Initiation
In A A A A*
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15. 15
Types of Addition Polymerizations
Ph
Anionic
C3H7 Li C4H9
Ph
Li+
Ph
n
C4H9
Ph Ph
Li+
n
Ph
Radical
PhCO2•
Ph
n
Ph
Cationic
Cl3Al OH2
H
Ph
HOAlCl3
Ph
n
H
Ph Ph
n
HOAlCl3
PhCO2
Ph
PhCO2
Ph Ph
n
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16. 16
Step-Growth Polymerization
Stage 1
Consumption
of monomer
n n
Stage 2
Combination
of small fragments
Stage 3
Reaction of
oligomers to give
high molecular
weight polymer
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17. 17
Step-Growth Polymerization
• Because high polymer does not form until the end
of the reaction, high molecular weight polymer is
not obtained unless high conversion of monomer
is achieved.
Xn =
1
1−p
Xn = Degree of polymerization
p = mole fraction monomer
conversion
1
10
100
1000
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1
Mole Fraction Conversion (p)
DegreeofPolymerization
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18. 18
Nylon-6,6
Cl Cl
O O
4
H2N NH24
Adipoyl chloride 1,6-Diaminohexane
Cl N
H
N
H
H
O O
4 4
NaOH
HO N
H
N
H
H
O O
4 4
n
6 carbon
diacid
6 carbon
diamine
Nylon-6,6
Diamine, NaOH, in H2O
Adipoyl chloride
in hexane
Nylon 6,6
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19. 19
Nylon-6,6
Diamine, NaOH, in H2O
Adipoyl chloride
in hexane
Nylon 6,6
Since the reactants are in different
phases, they can only react at the
phase boundary. Once a layer of
polymer forms, no more reaction
occurs. Removing the polymer allows
more reaction to occur.
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20. 20
Molecular Weight of Polymers
Unlike small molecules, polymers are typically a mixture of differently
sized molecules. Only an average molecular weight can be defined.
• Measuring molecular weight
• Size exclusion chromatography
• Viscosity
• Measurements of average molecular
weight (M.W.)
• Number average M.W. (Mn): Total
weight of all chains divided by # of
chains
• Weight average M.W. (Mw):
Weighted average. Always larger
than Mn
• Viscosity average M.W. (Mv):
Average determined by viscosity
measurements. Closer to Mw than
M
#
o
f
m
o
le
c
u
le
s
Mn
Mw
increasing molecular weight
Mv
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21. 21
What the Weights Mean
Mn: This gives you the true average weight
Let's say you had the following polymer sample:
2 chains: 1,000,000 Dalton 2,000,000
5 chains: 700,000 Dalton 3,500,000
10 chains: 400,000 Dalton 4,000,000
4 chains: 100,000 Dalton 400,000
2 chains: 50,000 Dalton 100,000
10,000,000
10,000,000/23 = 435,000 Dalton
1 Dalton = 1 g/mole
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22. 22
Weight Average Molecular Weight
Mw: Since most of the polymer mass is in the heavier fractions, this
gives the average molecular weight of the most abundant polymer
fraction by mass.
2,000,000
10,000,000
= 0.20×1,000,000 = 200,000
3,500,000
10,000,000
= 0.35× 700,000 = 245,000
4,000,000
10,000,000
= 0.40× 400,000 = 160,000
400,000
10,000,000
= 0.04 ×100,000 = 4,000
100,000
10,000,000
= 0.01× 50,000 = 500
Total = 609,500
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23. 23
Polymer Microstructure
Polyolefins with side chains have stereocenters on every other carbon
CH3
n
CH3 CH3 CH3 CH3 CH3 CH3CH3
With so many stereocenters, the stereochemistry can be complex.
There are three main stereochemical classifications for polymers.
Atactic: random orientation
Isotactic: All stereocenters have same orientation
Syndiotactic: Alternating stereochemistry
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24. 24
How to Determine Microstructure?
13
C NMR is a very powerful way to determine the microstructure of
a polymer.
13
C NMR shift is sensitive to the two
stereocenters on either side on sptectrometers
> 300 MHz. This is called pentad resolution.
r mm rmr
mmrm pentad
m = meso (same orientation)
r = racemic (opposite orientation)
12 1 2
13
C NMR spectrum of CH3 region
of atactic polypropylene
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25. 25
Why is this important?
• Tacticity affects the physical properties
– Atactic polymers will generally be amorphous, soft,
flexible materials
– Isotactic and syndiotactic polymers will be more
crystalline, thus harder and less flexible
• Polypropylene (PP) is a good example
– Atactic PP is a low melting, gooey material
– Isoatactic PP is high melting (176º), crystalline, tough
material that is industrially useful
– Syndiotactic PP has similar properties, but is very
clear. It is harder to synthesize
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