Download - Chapter 14: Polymer Structures - Iowa State Universitywordpress.engineering.iastate.edu/polycomp/files/2012/06/ch14.pdf · Chapter 14 - 4 Polymer Composition Most polymers are hydrocarbons

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Page 1: Chapter 14: Polymer Structures - Iowa State Universitywordpress.engineering.iastate.edu/polycomp/files/2012/06/ch14.pdf · Chapter 14 - 4 Polymer Composition Most polymers are hydrocarbons

Chapter 14 - 1

ISSUES TO ADDRESS...• What are the general structural and chemical

characteristics of polymer molecules?• What are some of the common polymeric

materials, and how do they differ chemically?• How is the crystalline state in polymers different

from that in metals and ceramics ?

Chapter 14:Polymer Structures

Page 2: Chapter 14: Polymer Structures - Iowa State Universitywordpress.engineering.iastate.edu/polycomp/files/2012/06/ch14.pdf · Chapter 14 - 4 Polymer Composition Most polymers are hydrocarbons

Chapter 14 - 2

What is a Polymer?

Poly mermany repeat unit

Adapted from Fig. 14.2, Callister & Rethwisch 8e.

C C C C C CHHHHHH

HHHHHH

Polyethylene (PE)ClCl Cl

C C C C C CHHH

HHHHHH

Poly(vinyl chloride) (PVC)HH

HHH H

Polypropylene (PP)

C C C C C CCH3

HH

CH3CH3H

repeatunit

repeatunit

repeatunit

Page 3: Chapter 14: Polymer Structures - Iowa State Universitywordpress.engineering.iastate.edu/polycomp/files/2012/06/ch14.pdf · Chapter 14 - 4 Polymer Composition Most polymers are hydrocarbons

Chapter 14 - 3

Ancient Polymers• Originally natural polymers were used

– Wood – Rubber– Cotton – Wool– Leather – Silk

• Oldest known uses– Rubber balls used by Incas– Noah used pitch (a natural polymer)

for the ark

Page 4: Chapter 14: Polymer Structures - Iowa State Universitywordpress.engineering.iastate.edu/polycomp/files/2012/06/ch14.pdf · Chapter 14 - 4 Polymer Composition Most polymers are hydrocarbons

Chapter 14 - 4

Polymer CompositionMost polymers are hydrocarbons

– i.e., made up of H and C• Saturated hydrocarbons

– Each carbon singly bonded to four other atoms– Example:

• Ethane, C2H6

C C

H

H H H

HH

Page 5: Chapter 14: Polymer Structures - Iowa State Universitywordpress.engineering.iastate.edu/polycomp/files/2012/06/ch14.pdf · Chapter 14 - 4 Polymer Composition Most polymers are hydrocarbons

Chapter 14 - 5

Page 6: Chapter 14: Polymer Structures - Iowa State Universitywordpress.engineering.iastate.edu/polycomp/files/2012/06/ch14.pdf · Chapter 14 - 4 Polymer Composition Most polymers are hydrocarbons

Chapter 14 - 6

Unsaturated Hydrocarbons• Double & triple bonds somewhat unstable –

can form new bonds– Double bond found in ethylene or ethene - C2H4

– Triple bond found in acetylene or ethyne - C2H2

C CH

H

H

H

C C HH

Page 7: Chapter 14: Polymer Structures - Iowa State Universitywordpress.engineering.iastate.edu/polycomp/files/2012/06/ch14.pdf · Chapter 14 - 4 Polymer Composition Most polymers are hydrocarbons

Chapter 14 - 7

Page 8: Chapter 14: Polymer Structures - Iowa State Universitywordpress.engineering.iastate.edu/polycomp/files/2012/06/ch14.pdf · Chapter 14 - 4 Polymer Composition Most polymers are hydrocarbons

Chapter 14 - 8

Isomerism• Isomerism

– two compounds with same chemical formula can have quite different structures

for example: C8H18• normal-octane

• 2,4-dimethylhexane

C C C C C C C CH

H

H

H

H

H

H

H

H

H

H

H

H

H

H

H

H

H H3C CH2 CH2 CH2 CH2 CH2 CH2 CH3=

H3C CH

CH3

CH2 CH

CH2

CH3

CH3

H3C CH2 CH3( )6

Page 9: Chapter 14: Polymer Structures - Iowa State Universitywordpress.engineering.iastate.edu/polycomp/files/2012/06/ch14.pdf · Chapter 14 - 4 Polymer Composition Most polymers are hydrocarbons

Chapter 14 - 9

Polymerization and Polymer Chemistry

• Free radical polymerization

• Initiator: example - benzoyl peroxide

C

H

H

O O C

H

H

C

H

H

O2

C C

H H

HHmonomer(ethylene)

R +

free radical

R C C

H

H

H

H

initiation

R C C

H

H

H

H

C C

H H

HH

+ R C C

H

H

H

H

C C

H H

H H

propagation

dimer

R= 2

Page 10: Chapter 14: Polymer Structures - Iowa State Universitywordpress.engineering.iastate.edu/polycomp/files/2012/06/ch14.pdf · Chapter 14 - 4 Polymer Composition Most polymers are hydrocarbons

Chapter 14 -10

Chemistry and Structure of Polyethylene

Adapted from Fig. 14.1, Callister & Rethwisch 8e.

Note: polyethylene is a long-chain hydrocarbon- paraffin wax for candles is short polyethylene

Page 11: Chapter 14: Polymer Structures - Iowa State Universitywordpress.engineering.iastate.edu/polycomp/files/2012/06/ch14.pdf · Chapter 14 - 4 Polymer Composition Most polymers are hydrocarbons

Chapter 14 -11

Bulk or Commodity Polymers

Page 12: Chapter 14: Polymer Structures - Iowa State Universitywordpress.engineering.iastate.edu/polycomp/files/2012/06/ch14.pdf · Chapter 14 - 4 Polymer Composition Most polymers are hydrocarbons

Chapter 14 -12

Bulk or Commodity Polymers (cont)

Page 13: Chapter 14: Polymer Structures - Iowa State Universitywordpress.engineering.iastate.edu/polycomp/files/2012/06/ch14.pdf · Chapter 14 - 4 Polymer Composition Most polymers are hydrocarbons

Chapter 14 -13

Bulk or Commodity Polymers (cont)

Page 14: Chapter 14: Polymer Structures - Iowa State Universitywordpress.engineering.iastate.edu/polycomp/files/2012/06/ch14.pdf · Chapter 14 - 4 Polymer Composition Most polymers are hydrocarbons

Chapter 14 -14

Page 15: Chapter 14: Polymer Structures - Iowa State Universitywordpress.engineering.iastate.edu/polycomp/files/2012/06/ch14.pdf · Chapter 14 - 4 Polymer Composition Most polymers are hydrocarbons

Chapter 14 -

VMSE: Polymer Repeat Unit Structures

15

Manipulate and rotate polymer structures in 3-dimensions

Page 16: Chapter 14: Polymer Structures - Iowa State Universitywordpress.engineering.iastate.edu/polycomp/files/2012/06/ch14.pdf · Chapter 14 - 4 Polymer Composition Most polymers are hydrocarbons

Chapter 14 -16

MOLECULAR WEIGHT• Molecular weight, M: Mass of a mole of chains.

Low M

high M

Not all chains in a polymer are of the same length— i.e., there is a distribution of molecular weights

Page 17: Chapter 14: Polymer Structures - Iowa State Universitywordpress.engineering.iastate.edu/polycomp/files/2012/06/ch14.pdf · Chapter 14 - 4 Polymer Composition Most polymers are hydrocarbons

Chapter 14 -17

xi = number fraction of chains in size range i

molecules of #totalpolymer of wttotal

nM

MOLECULAR WEIGHT DISTRIBUTION

M n xi Mi

M w wi Mi

Adapted from Fig. 14.4, Callister & Rethwisch 8e.

wi = weight fraction of chains in size range i

Mi = mean (middle) molecular weight of size range i

Page 18: Chapter 14: Polymer Structures - Iowa State Universitywordpress.engineering.iastate.edu/polycomp/files/2012/06/ch14.pdf · Chapter 14 - 4 Polymer Composition Most polymers are hydrocarbons

Chapter 14 -18

Molecular Weight Calculation

Example: average mass of a classStudent Weight

mass (lb)1 1042 1163 1404 1435 1806 1827 1918 2209 225

10 380

What is the averageweight of the students inthis 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?

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Chapter 14 -19

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 number of mean number weightrange students weight fraction fraction

Ni Wi xi wi

mass (lb) mass (lb)81-120 2 110 0.2 0.117121-160 2 142 0.2 0.150161-200 3 184 0.3 0.294201-240 2 223 0.2 0.237241-280 0 - 0 0.000281-320 0 - 0 0.000321-360 0 - 0 0.000361-400 1 380 0.1 0.202

Ni NiWi

10 1881total

numbertotal

weight

Calculate the number and weight fraction of students in each weight range as follows:

xi

Ni

Ni wi

NiWi

NiWi

For example: for the 81-120 lb range

x81120

210

0.2

117.01881

011 x 212081 w

Page 20: Chapter 14: Polymer Structures - Iowa State Universitywordpress.engineering.iastate.edu/polycomp/files/2012/06/ch14.pdf · Chapter 14 - 4 Polymer Composition Most polymers are hydrocarbons

Chapter 14 -20

Molecular Weight Calculation (cont.)

Mn xiMi (0.2 x 110 0.2 x 142+ 0.3 x 184+ 0.2 x 223+ 0.1 x 380) =188 lb

weight mean number weightrange weight fraction fraction

Wi xi wi

mass (lb) mass (lb)81-120 110 0.2 0.117

121-160 142 0.2 0.150161-200 184 0.3 0.294201-240 223 0.2 0.237241-280 - 0 0.000281-320 - 0 0.000321-360 - 0 0.000361-400 380 0.1 0.202

Mw wiMi (0.117 x 110 0.150 x 142+ 0.294 x 184

+ 0.237 x 223+ 0.202 x 380) = 218 lb Mw wiMi 218 lb

Page 21: Chapter 14: Polymer Structures - Iowa State Universitywordpress.engineering.iastate.edu/polycomp/files/2012/06/ch14.pdf · Chapter 14 - 4 Polymer Composition Most polymers are hydrocarbons

Chapter 14 -21

Degree of Polymerization, DPDP = average number of repeat units per chain

iimfm

m

:follows as calculated is this copolymers forunit repeat of weightmolecular average where

C C C C C C C CH

H

H

H

H

H

H

H

H

H

H

H

H

H

H

H

H

C C C C

H

H

H

H

H

H

H

H

H( ) DP = 6

mol. wt of repeat unit iChain fraction

mMDP n

Page 22: Chapter 14: Polymer Structures - Iowa State Universitywordpress.engineering.iastate.edu/polycomp/files/2012/06/ch14.pdf · Chapter 14 - 4 Polymer Composition Most polymers are hydrocarbons

Chapter 14 -22

Adapted from Fig. 14.7, Callister & Rethwisch 8e.

Molecular Structures for Polymers

Branched Cross-Linked NetworkLinear

secondarybonding

Page 23: Chapter 14: Polymer Structures - Iowa State Universitywordpress.engineering.iastate.edu/polycomp/files/2012/06/ch14.pdf · Chapter 14 - 4 Polymer Composition Most polymers are hydrocarbons

Chapter 14 -23

Polymers – Molecular ShapeMolecular Shape (or Conformation) – chain

bending and twisting are possible by rotation of carbon atoms around their chain bonds– note: not necessary to break chain bonds

to alter molecular shape

Adapted from Fig. 14.5, Callister & Rethwisch 8e.

Page 24: Chapter 14: Polymer Structures - Iowa State Universitywordpress.engineering.iastate.edu/polycomp/files/2012/06/ch14.pdf · Chapter 14 - 4 Polymer Composition Most polymers are hydrocarbons

Chapter 14 -24

Chain End-to-End Distance, r

Adapted from Fig. 14.6, Callister & Rethwisch 8e.

Page 25: Chapter 14: Polymer Structures - Iowa State Universitywordpress.engineering.iastate.edu/polycomp/files/2012/06/ch14.pdf · Chapter 14 - 4 Polymer Composition Most polymers are hydrocarbons

Chapter 14 -25

Molecular Configurations for Polymers

Configurations – to change must break bonds• Stereoisomerism

EB

A

D

C C

D

A

BE

mirror plane

C CR

HH

HC C

H

H

H

R

or C C

H

H

H

R

Stereoisomers are mirrorimages – can’t superimposewithout breaking a bond

Page 26: Chapter 14: Polymer Structures - Iowa State Universitywordpress.engineering.iastate.edu/polycomp/files/2012/06/ch14.pdf · Chapter 14 - 4 Polymer Composition Most polymers are hydrocarbons

Chapter 14 -26

TacticityTacticity – stereoregularity or spatial arrangement of R

units along chain

C C

H

H

H

R R

H

H

H

CC

R

H

H

H

CC

R

H

H

H

CC

isotactic – all R groups on same side of chain

C C

H

H

H

R

C C

H

H

H

R

C C

H

H

H

R R

H

H

H

CC

syndiotactic – R groups alternate sides

Page 27: Chapter 14: Polymer Structures - Iowa State Universitywordpress.engineering.iastate.edu/polycomp/files/2012/06/ch14.pdf · Chapter 14 - 4 Polymer Composition Most polymers are hydrocarbons

Chapter 14 -27

Tacticity (cont.)

atactic – R groups randomlypositioned

C C

H

H

H

R R

H

H

H

CC

R

H

H

H

CC

R

H

H

H

CC

Page 28: Chapter 14: Polymer Structures - Iowa State Universitywordpress.engineering.iastate.edu/polycomp/files/2012/06/ch14.pdf · Chapter 14 - 4 Polymer Composition Most polymers are hydrocarbons

Chapter 14 -28

cis/trans Isomerism

C CHCH3

CH2 CH2

C CCH3

CH2

CH2

H

ciscis-isoprene

(natural rubber)

H atom and CH3 group on same side of chain

transtrans-isoprene (gutta percha)

H atom and CH3 group on opposite sides of chain

Page 29: Chapter 14: Polymer Structures - Iowa State Universitywordpress.engineering.iastate.edu/polycomp/files/2012/06/ch14.pdf · Chapter 14 - 4 Polymer Composition Most polymers are hydrocarbons

Chapter 14 -

VMSE: Stereo and Geometrical Isomers

29Chapter 7 - 19

Manipulate and rotate polymer structures in 3-dimensions

Page 30: Chapter 14: Polymer Structures - Iowa State Universitywordpress.engineering.iastate.edu/polycomp/files/2012/06/ch14.pdf · Chapter 14 - 4 Polymer Composition Most polymers are hydrocarbons

Chapter 14 -30

Copolymerstwo or more monomers

polymerized together • random – A and B randomly

positioned along chain• alternating – A and B

alternate in polymer chain• block – large blocks of A

units alternate with large blocks of B units

• graft – chains of B units grafted onto A backbone

A – B –

random

block

graft

Adapted from Fig. 14.9, Callister & Rethwisch 8e.

alternating

Page 31: Chapter 14: Polymer Structures - Iowa State Universitywordpress.engineering.iastate.edu/polycomp/files/2012/06/ch14.pdf · Chapter 14 - 4 Polymer Composition Most polymers are hydrocarbons

Chapter 14 -31

Crystallinity in Polymers• Ordered atomic

arrangements involving molecular chains

• Crystal structures in terms of unit cells

• Example shown– polyethylene unit cell

Adapted from Fig. 14.10, Callister & Rethwisch 8e.

Page 32: Chapter 14: Polymer Structures - Iowa State Universitywordpress.engineering.iastate.edu/polycomp/files/2012/06/ch14.pdf · Chapter 14 - 4 Polymer Composition Most polymers are hydrocarbons

Chapter 14 -32

Polymer Crystallinity• Crystalline regions

– thin platelets with chain folds at faces– Chain folded structure

10 nm

Adapted from Fig. 14.12, Callister & Rethwisch 8e.

Page 33: Chapter 14: Polymer Structures - Iowa State Universitywordpress.engineering.iastate.edu/polycomp/files/2012/06/ch14.pdf · Chapter 14 - 4 Polymer Composition Most polymers are hydrocarbons

Chapter 14 -33

Polymer Crystallinity (cont.)Polymers rarely 100% crystalline• Difficult for all regions of all chains to

become aligned

• Degree of crystallinity expressed as % crystallinity.-- Some physical properties

depend on % crystallinity.-- Heat treating causes

crystalline regions to grow and % crystallinity to increase.

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.)

crystalline region

amorphousregion

Page 34: Chapter 14: Polymer Structures - Iowa State Universitywordpress.engineering.iastate.edu/polycomp/files/2012/06/ch14.pdf · Chapter 14 - 4 Polymer Composition Most polymers are hydrocarbons

Chapter 14 -34

Polymer Single Crystals• Electron micrograph – multilayered single crystals

(chain-folded layers) of polyethylene• Single crystals – only for slow and carefully controlled

growth rates

Adapted from Fig. 14.11, Callister & Rethwisch 8e.

Page 35: Chapter 14: Polymer Structures - Iowa State Universitywordpress.engineering.iastate.edu/polycomp/files/2012/06/ch14.pdf · Chapter 14 - 4 Polymer Composition Most polymers are hydrocarbons

Chapter 14 -35

Semicrystalline Polymers

Spherulite surface

Adapted from Fig. 14.13, Callister & Rethwisch 8e.

• Some semicrystalline polymers form spherulite structures

• Alternating chain-folded crystallites and amorphous regions

• Spherulite structure for relatively rapid growth rates

Page 36: Chapter 14: Polymer Structures - Iowa State Universitywordpress.engineering.iastate.edu/polycomp/files/2012/06/ch14.pdf · Chapter 14 - 4 Polymer Composition Most polymers are hydrocarbons

Chapter 14 -36

Photomicrograph – Spherulites in Polyethylene

Adapted from Fig. 14.14, Callister & Rethwisch 8e.

Cross-polarized light used -- a maltese cross appears in each spherulite