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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
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