Chapter 14: Polymer Structures - Iowa State 14 - 4 Polymer Composition Most polymers are...

download Chapter 14: Polymer Structures - Iowa State 14 - 4 Polymer Composition Most polymers are hydrocarbons – i.e., made up of H and C • Saturated hydrocarbons ... H = H3CCH2 CH2 CH2

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Transcript of Chapter 14: Polymer Structures - Iowa State 14 - 4 Polymer Composition Most polymers are...

  • 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

  • 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

  • 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

  • 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

  • Chapter 14 - 5

  • 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

  • Chapter 14 - 7

  • 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

    CH3CH2 CH

    CH2

    CH3

    CH3

    H3C CH2 CH3( )6

  • 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

  • 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

  • Chapter 14 -11

    Bulk or Commodity Polymers

  • Chapter 14 -12

    Bulk or Commodity Polymers (cont)

  • Chapter 14 -13

    Bulk or Commodity Polymers (cont)

  • Chapter 14 -14

  • Chapter 14 -

    VMSE: Polymer Repeat Unit Structures

    15

    Manipulate and rotate polymer structures in 3-dimensions

  • 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

  • Chapter 14 -17

    xi = number fraction of chains in size range i

    molecules of #totalpolymer of wttotal

    nM

    MOLECULAR WEIGHT DISTRIBUTION

    M n xi MiM 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

  • 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?

  • 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 wimass (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 NiWi10 1881

    total number

    total weight

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

    xi

    NiNi

    wi NiWi

    NiWi

    For example: for the 81-120 lb range

    x81120

    210

    0.2

    117.01881

    011 x 212081 w

  • 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 wimass (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

  • 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

  • Chapter 14 -22

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

    Molecular Structures for Polymers

    Branched Cross-Linked NetworkLinear

    secondarybonding

  • 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.

  • Chapter 14 -24

    Chain End-to-End Distance, r

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

  • 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 cant superimposewithout breaking a bond

  • 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

  • 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

  • Chapter 14 -28

    cis/trans Isomerism

    C CHCH3

    CH2 CH2C C

    CH3

    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

  • Chapter 14 -

    VMSE: Stereo and Geometrical Isomers

    29Chapter 7 - 19

    Manipulate and rotate polymer structures in 3-dimensions

  • 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

  • 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.

  • 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.

  • 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 Structur