Download Chapter 14: Polymer Structure

Chapter 4:
Polymer Structures
ISSUES TO ADDRESS...
• What are the general _____________________
characteristics of polymer molecules?
• What are some of the
____________________
materials,
and how do
theyindiffer
_________?
• How
is the ________
state
polymers
different
from that in metals and ceramics ?
Chapter 4 - 1
What is a Polymer?
Poly
many
mer
repeat unit
repeat
unit
repeat
unit
repeat
unit
H H H H H H
C C C C C C
H H H H H H
H H H H H H
C C C C C C
H Cl H Cl H Cl
Polyethylene (PE)
Poly(vinyl chloride) (PVC)
H
C
H
H H
C C
CH3 H
H H
C C
CH3 H
H
C
CH3
Polypropylene (PP)
Adapted from Fig. 4.2, Callister & Rethwisch 4e.
Chapter 4 - 2
Ancient Polymers
• Originally _______________ were used
– Wood
– ________
– Cotton
– Wool
– _________
– Silk
• Oldest known uses
– Rubber balls ____________
– Noah used _______ (a natural polymer)
for the ark
Chapter 4 - 3
Polymer Composition
Most polymers are _________________
– i.e., made up of H and C
• Saturated hydrocarbons
– Each _______ singly bonded to four other atoms
– Example:
• Ethane, C2H6
H
H
C
H
H
C
H
H
Chapter 4 - 4
Chapter 4 - 5
Unsaturated Hydrocarbons
• _______________ somewhat unstable – can
form new bonds
– _______ bond found in ethylene or ethene - C2H4
H
H
C C
H
H
– ______ bond found in acetylene or ethyne - C2H2
H C C H
Chapter 4 - 6
Isomerism
• ______________
– two _________ with same _______________ can
have quite different structures
for example: C8H18
• normal-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
6
• 2,4-dimethylhexane
CH3
H3C CH CH2 CH CH3
CH2
CH3
Chapter 4 - 7
Polymerization and
Polymer Chemistry
• ______________ polymerization
R
+
H H
H H
H H
C C
R C C
H H
monomer
(ethylene)
free radical
R C C
H H
+
initiation
H H
H H
H H H H
C C
R C C C C
H H
H H H H
propagation
dimer
• ________: example - benzoyl peroxide
H
C O O C
H
H
H
H
2
C O
=2R
H
Chapter 4 - 8
Chemistry and Structure of
Polyethylene
Adapted from Fig.
4.1, Callister &
Rethwisch 4e.
Note: ___________ is a long-chain hydrocarbon
- paraffin wax for candles is short polyethylene
Chapter 4 - 9
Bulk or Commodity Polymers
Chapter 4 - 10
Bulk or Commodity Polymers (cont)
Chapter 4 - 11
Bulk or Commodity Polymers (cont)
Chapter 4 - 12
VMSE: Polymer Repeat Unit Structures
Manipulate and rotate polymer structures in 3-dimensions
Chapter 4 - 13
MOLECULAR WEIGHT
• Molecular weight, M: __________________________.
Low M
high M
Not all chains in a polymer are of the same length
— i.e., there is a distribution of molecular weights
Chapter 4 - 14
MOLECULAR WEIGHT DISTRIBUTION
Adapted from Fig. 4.4, Callister & Rethwisch 4e.
total wt of polymer
Mn =
total # of molecules
M n = Sxi Mi
M w = Swi Mi
Mi = ___________ molecular weight of size range i
xi = __________________ of chains in size range i
wi = __________________ of chains in size range i
Chapter 4 - 15
Molecular Weight Calculation
Example: average mass of a class
Student
Weight
mass (lb)
1
104
2
116
3
140
4
143
5
180
6
182
7
191
8
220
9
225
10
380
What is the average
weight of the students in
this class:
a) Based on the number
fraction of students in
each mass range?
b) Based on the weight
fraction of students in
each mass range?
Chapter 4 - 16
Molecular Weight Calculation (cont.)
Solution: The first step is to sort the students into weight ranges.
Using 40 lb ranges gives the following table:
weight
range
number of
students
mean
weight
Ni
Wi
mass (lb)
81-120
121-160
161-200
201-240
241-280
281-320
321-360
361-400
2
2
3
2
0
0
0
1
110
142
184
223
380
total
number
SNi
10
SNiWi
1881
mass (lb)
number
Calculateweight
the number and weight
fraction
fraction
fraction of
students in each weight
xrange
wi
as follows:
i
NiWi
Ni
wi =
xi =
0.2
Ni
å NiWi
å0.117
0.2
0.150
0.3
0.294
For example:
for the 81-120 lb range
0.2
0.237
2
0 x
0.000
= 0.2
81-120 =
0
0.000
10
0
0.0002 x 110
=
= 0.117
0.1 w 81-120
0.202
1881
total
weight
Chapter 4 - 17
Molecular Weight Calculation (cont.)
weight
range
mean
weight
mass (lb)
Wi
mass (lb)
81-120
121-160
161-200
201-240
241-280
281-320
321-360
361-400
110
142
184
223
380
number
fraction
xi
weight
fraction
wi
0.2
0.2
0.3
0.2
0
0
0
0.1
0.117
0.150
0.294
0.237
0.000
0.000
0.000
0.202
Mn = å xi Mi = (0.2 x 110 + 0.2 x 142 + 0.3 x 184 + 0.2 x 223 + 0.1 x 380) = 188 lb
Mw = å wi Mi = (0.117 x 110 + 0.150 x 142 + 0.294 x 184
Mw = å wi Mi = 218 lb
+ 0.237 x 223 + 0.202 x 380) = 218 lb
Chapter 4 - 18
Degree of Polymerization, DP
DP = average number of ___________ 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
DP = 6
H H H H H H H H H H H H
Mn
DP =
m
where m = average molecular weight of repeat unit
for copolymers this is calculated as follows:
m = Sfi mi
Chain fraction
mol. wt of repeat unit i
Chapter 4 - 19
Molecular Structures for Polymers
secondary
bonding
Linear
Branched
Cross-Linked
Network
Adapted from Fig. 4.7, Callister & Rethwisch 4e.
Chapter 4 - 20
Polymers – Molecular Shape
Molecular Shape (or ______________) – chain
bending and twisting are possible by rotation
of carbon atoms _____________________
– note: not necessary to _______________
to alter molecular shape
Adapted from Fig.
4.5, Callister &
Rethwisch 4e.
Chapter 4 - 21
Chain End-to-End Distance, r
Adapted from Fig.
4.6, Callister &
Rethwisch 4e.
Chapter 4 - 22
Molecular Configurations for Polymers
_____________– to change must break bonds
• _________________
H
H
C C
H
H H
H R
or
C C
R
Stereoisomers are mirror
images – can’t superimpose
without breaking a bond
C C
H R
B
H H
A
A
C
C
E
E
D
D
B
mirror
plane
Chapter 4 - 23
Tacticity
________ – ____________ or spatial arrangement of
R units along chain
________ – all R groups on
same side of chain
__________ – R groups
alternate sides
H H H H H H H H
H H H R H H H R
C C C C C C C C
C C C C C C C C
H R H R H R H R
H R H H H R H H
Chapter 4 - 24
Tacticity (cont.)
_____ – R groups randomly
positioned
H H H H H R H H
C C C C C C C C
H R H R H H H R
Chapter 4 - 25
cis/trans Isomerism
CH3
H
CH3
C C
CH2
CH2
C C
CH2
CH2
H
cis
trans
cis-isoprene
(natural rubber)
trans-isoprene
(gutta percha)
H atom and CH3 group on
______ side of chain
H atom and CH3 group on
________ sides of chain
Chapter 4 - 26
VMSE: Stereo and Geometrical Isomers
Manipulate and rotate polymer structures in 3-dimensions
Chapter 74--19
27
Copolymers
two or more monomers
polymerized together
• ______ – A and B randomly
positioned along chain
• __________ – A and B
alternate in polymer chain
• ________ – large blocks of
A units alternate with large
blocks of B units
• _______ – chains of B units
grafted onto A backbone
A–
B–
Adapted from Fig.
4.9, Callister &
Rethwisch 4e.
random
alternating
block
graft
Chapter 4 - 28
Crystallinity in Polymers
Adapted from Fig.
4.10, Callister &
Rethwisch 4e.
• Ordered atomic
arrangements involving
__________________
• Crystal structures in terms
of ___________
• Example shown
– ___________ unit cell
Chapter 4 - 29
Polymer Crystallinity
• Crystalline regions
– thin _______ with chain folds at faces
– ____________ structure
Adapted from Fig.
4.12, Callister &
Rethwisch 4e.
10 nm
Chapter 4 - 30
Polymer Crystallinity (cont.)
Polymers rarely _________________
• Difficult for all regions of all chains to
become aligned
crystalline
region
• Degree of crystallinity
expressed as ___________.
-- Some physical properties
depend on % crystallinity.
-- _________________ causes
crystalline regions to grow
and % crystallinity to
increase.
amorphous
region
Adapted from Fig. 14.11, Callister 6e.
(Fig. 14.11 is from H.W. Hayden, W.G. Moffatt,
and J. Wulff, The Structure and Properties of
Materials, Vol. III, Mechanical Behavior, John Wiley
and Sons, Inc., 1965.)
Chapter 4 - 31
Polymer Single Crystals
• ___________________ – multilayered single crystals
(chain-folded layers) of polyethylene
• _____________ – only for slow and carefully controlled
growth rates
Adapted from Fig. 4.11, Callister & Rethwisch 4e.
Chapter 4 - 32
Semicrystalline Polymers
Spherulite
surface
• Some semicrystalline
polymers form
__________ structures
• ________ chain-folded
crystallites and
amorphous regions
• ________ structure for
relatively rapid growth
rates
Adapted from Fig. 4.13, Callister & Rethwisch 4e.
Chapter 4 - 33
Photomicrograph – Spherulites in
Polyethylene
______________ light used
-- a maltese cross appears in each ____________
Adapted from Fig. 4.14, Callister & Rethwisch 4e.
Chapter 4 - 34