This document discusses polymer structure and composition. It begins by describing natural polymers like wood, cotton and rubber that were originally used. It then discusses the development of synthetic polymers like plastics, rubbers and fibers. Most polymers are hydrocarbons made of carbon and hydrogen. Polymers can have different compositions and structures including linear, branched, cross-linked and network configurations. The properties of a polymer depend on factors like its molecular weight, end-to-end distance, tacticity and crystallinity. Common techniques for characterizing polymers include determining the number average and weight average molecular weights.

1. POLYMER
STRUCTURES
Desiree Jane Enriquez
Sarah Reyes
Bernald Cabrera
Nephtalie Cruz
Arwie Mendoza
1

2. POLYMER
2

3. Polymer History
Originally natural polymers
were used in
Wood
Cotton
Leather
Rubber
Wool
Silk
Synthetic Polymers
Plastics
Rubbers
Fiber materials
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4. Polymer Composition
Most polymers are hydrocarbons
– i.e. made up of H and C
Saturated hydrocarbons
◦ Each carbon bonded to four other atoms
H
H
C
H
H
C
H
H
CnH2n+2
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5. 5

6. Unsaturated Hydrocarbons
Double & triple bonds relatively reactive
– can form new bonds
 Double bond – ethylene or ethene - CnH2n
H
H
C C
H
H
H C C H
4-bonds, but only 3 atoms bound to C’s
 Triple bond – acetylene or ethyne - CnH2n-2
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7. Isomerism
 Isomerism
◦ two compounds with same chemical formula can
have quite different structures
Ex: C8H18
 n-octane
H H H H H H H H
H C C C C C C C C H
= H3C CH2 CH2 CH2 CH2 CH2 CH2 CH3
⇓
H H H H H H H H
H3C ( CH2 ) CH3
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 2-methyl-4-ethyl pentane (isooctane)
CH3
H3C CH CH2 CH CH3
CH2
CH3
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8. Chemistry of Polymers
 Free
radical polymerization
H H
C C
+
R
R C C
H H
monomer
(ethylene)
free radical
H H
R C C
H H
initiation
H H
H H
+
H H
H H H H
C C
R C C C C
H H
H H H H
propagation
dimer
 Initiator:
H
example - benzoyl peroxide
C O O C
H
H
H
H
2
C O
=2R
H
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9. Chemistry of Polymers
Note: polyethylene is just a long HC
- paraffin is short polyethylene
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10. Bulk or Commodity Polymers
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11. 11

12. 12

13. MOLECULAR WEIGHT
low M
high M
Not all chains in a polymer are of the same length
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14. Molecular weight
◦ The properties of a polymer depend on its length
◦ synthesis yields polymer distribution of lengths
◦ Define “average” molecular weight
◦ Two approaches are typically taken
 Number average molecular weight (Mn)
 Weight-average molecular weight (Mw)

15. Molecular mass example

16. Degree of Polymerization, n
n = number of repeat units per chain
H H H H H H H H H H H H
H C C (C C ) C C C C C C C C H
ni = 6
H H H H H H H H H H H H
Mn
nn = ∑ xi ni =
m
Mw
nw = ∑ wi ni =
m
where m = average molecular weight of repeat unit
m = Σf i mi
Chain fraction
mol. wt of repeat unit i
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17. End to End Distance, r
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18. Molecular Structures
• Covalent chain configurations and strength:
secondary
bonding
Linear
Branched
Cross-Linked
Network
Direction of increasing strength
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19. Polymers – Molecular Shape
Conformation – Molecular orientation
can be changed by rotation around the
bonds
◦ note: no bond breaking needed
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20. Polymers – Molecular Shape
Configurations – to change must break bonds
Stereoisomerism
H
H H
H
C C
H
H R
or
C C
R
C C
H R
H H
A
A
C
B
E
C
E
D
D
B
mirror
plane
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21. Tacticity
Tacticity – stereoregularity of chain
isotactic – all R groups on
same side of chain
H H H H H H H H
C C C C C C C C
H R H R H R H R
H H H R H H H R
syndiotactic – R groups
alternate sides
C C C C C C C C
H R H H H R H H
H H H H H R H H
atactic – R groups random
C C C C C C C C
H R H R H H H R
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22. cis/trans Isomerism
CH3
H
C C
CH2
CH2
CH3
C C
CH2
CH2
H
cis
trans
cis-isoprene
(natural rubber)
trans-isoprene
(gutta percha)
bulky groups on same side
of chain
bulky groups on opposite
sides of chain
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23. Copolymers
two or more monomers
polymerized together
 random – A and B randomly
vary in chain
 alternating – A and B
alternate in polymer chain
 block – large blocks of A
alternate with large blocks of
B
 graft – chains of B grafted on
to A backbone
A–
random
alternating
block
B–
graft
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24. Polymer Crystallinity
Ex: polyethylene unit cell
Crystals must contain the polymer
chains in some way
◦ Chain folded structure
10 nm
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25. Polymer Crystallinity
Polymers rarely 100% crystalline

Too difficult to get all those chains
aligned
• %
Crystallinity: % of material
that is crystalline.
-- TS and E often increase
with % crystallinity.
-- Annealing causes
crystalline regions
to grow. % crystallinity
increases.
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26. Polymer Crystal Forms
 Single
crystals – only if slow careful growth
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27. Polymer Crystal Forms
 Spherulites
– fast
growth – forms lamellar
(layered) structures
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28. Spherulites – crossed polarizers
Maltese cross
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