Polymer SynthesisCHEM 421

Reading (Odian Book):

Chapter 8-1, 8-2

Polymer SynthesisCHEM 421

Polymer Parameters

• Chemical structure– Chemical composition and distribution

– Sequence length and distribution

• Molecular weight and distribution

• Chain isomerism

• Morphology

• Topology

• Additives

• Cost

Polymer SynthesisCHEM 421

Chain Isomerism

• Regio-isomers

• Geometric isomers

• Stereo-isomers

• Conformational isomers

Polymer SynthesisCHEM 421

Geometric Isomers

CH2

CH CH

CH2

n

CH2

CH CH

CH2

n

CH2 CH

n

• 1,3-butadiene

– cis-1,4-polybutadiene

» Tg = - 90 °C

» Tm = N/A (amorphous)

– trans-1,4-polybutadiene

» Tg = - 63 °C

» Tm = 100 °C

– 1,2-atactic-polybutadiene

» Tg = 0 °C

Polymer SynthesisCHEM 421

“Cis” vs. “Trans” Fats…

• Animal fats and vegetable oils– Vegetable oils polyunsaturated

(several double bonds)

– Solid fats saturated

(no double bonds)

• Hardening– Convert liquid oils to solid fats…hydrogenation

CH2

CH

O C

O

CH2 CH3

CH2

O C

O

CH2 CH CH CH2 CH3

O C

O

CH2 CH CH CH2 CH CH CH2 CH3

14

7 7

7 4

H2

PtFat

Polymer SynthesisCHEM 421

Chain Isomerism

• Regio-isomers

• Geometric isomers

• Stereo-isomers

• Conformational isomers

Polymer SynthesisCHEM 421

Stereoisomers

• “tacticity”

–Greek: “to put in order”

• Planar zig-zag conformation

• Relative configurations

• Isotactic

... ...

H H H H H

X X X X

H

H

H

H

H

H

H

H

H

Asymmetric carbons

Polymer SynthesisCHEM 421

Stereoisomers

• Isotactic

• Syndiotactic

• Atactic

... ...

H H H H H

X X X X

H

H

H

H

H

H

H

H

H

... ...

H H H H H

X H X H

H

H

H

X

H

H

H

X

H

... ...

H H H H H

X X H X

H

H

H

H

H

X

H

H

H

Polymer SynthesisCHEM 421

Model Systemsmeso- and racemic 2,4-disubstituted pentane

H3C CH3

H

X X

H

H3C CH3

X

H

X

H

CH3H3C

X XH

H

CH3H3C

X H

H X

meso

rac

Polymer SynthesisCHEM 421

Model Systemsmeso- and racemic 2,4-disubstituted pentane

H3C CH3

H

X X

H

CH3H3C

X XH

H

mesoa

b

H3C CH3

X

H

X

H

CH3H3C

X H

H Xrac

a

a

Polymer SynthesisCHEM 421

“Dyad” Analysis of Polymer Chains

X XH

H

... ...Meso dyad (m)

X H

H X

... ...

Rac dyad (r)

a

b

a

a

Polymer SynthesisCHEM 421

“Dyad” Analysis of Polymer Chains

X XX

... ...X XX

X X

... ...X

X X X

Isotactic (mm)

Syndiotactic (rr)

X X

... ...X

X X X

Atactic or heterotactic (rm)

Polymer SynthesisCHEM 421

Why does stereochemistry matter?

CH2 CH

n

Atactic polystyrene Tg = 105 °C Tm = N/A

Syndiotactic polystyrene Tg = 105 °C Tm = 270 °C

Polymer SynthesisCHEM 421

Why does stereochemistry matter?

CH2 CH

CH3n

Polymer SynthesisCHEM 421

Why does stereochemistry matter?

Isotactic Syndiotactic Atactic

Tm

(°C)165 135 N/A

Density

(g/mL)0.92 –

0.94 0.89 – 0.91 0.85

Solubility(Hydrocarbons at

Room Temp)

none medium high

Strength high medium low

CH2 CH

CH3n

Polymer SynthesisCHEM 421

Stereochemistry and Synthesis

60 MHz 1H NMR spectrum ofpoly(methyl methacrylate)made using different initiators

(A) Free Radical

(B) Anionic

CH2 C

C

n

CH3

O

O

CH3

Polymer SynthesisCHEM 421

“Dyad” Analysis of Polymer Chains

Meso dyad (m)

Rac dyad (r)

C CH

H

... ...

O OCH3 O OCH3

CH3 CH3b

a

aC CH3H

H

... ...

O OCH3

CH3 C

O OCH3

a

Methylene centered around 2.2 ppm

Free radical polymer: predominantly syndiotactic

Anionic polymer: predominantly isotactic

Free radical

Anionic

Polymer SynthesisCHEM 421

Polymer SynthesisCHEM 421

“Dyad” Analysis of Polymer Chains

Methylene Perspective

C CH

H

... ...

O OCH3 O OCH3

CH3 CH3b

a

Methyl Perspective

C CH3H

H

... ...

O OCH3

CH3 C

O OCH3

H

H

C

O OCH3

CH3

Need two monomer units to “look”or to “use” methylene protons forcharacterizing stereochemistry…

Need three monomer units to “look”or to “use” α-methyl group forcharacterizing stereochemistry…

m

rr

Polymer SynthesisCHEM 421

Polymer SynthesisCHEM 421

Polymer SynthesisCHEM 421

Chain Isomerism

• Regio-isomers

• Stereo-isomers

• Geometric isomers

• Conformational isomers