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