Page 792 - Carrahers_Polymer_Chemistry,_Eighth_Edition

Stereogeometry of Polymers 755

The second pair contains racemic diads and is syndiotactic by the meso, racemic argument but
with the chloride atoms on the same side.

CI CI
H H
Syndiotactic
R R
H
CI
Racemic
Racemic

We will now consider segments of a polymer derived from the polymerization of propylene
oxide. Here the simplest approach is to simply consider this an extension of the case immediately
above except where the chloride atoms are substituted by methyl radicals and the next methylene
is now an oxygen atom. Thus, we can make the same assignments based on the meso, racemic
considerations.

C H
H 3
R O O R
Syndiotactic
O
H C H H C H
3
3

H CH 3
R O O R
O
Isotactic
H C H H C H
3
3

H 3 C H
R O O R
Atactic O
C H CH 3
H 3 H

Similarity, we can make assignments for poly(lactic acid) except considering that the carbon
next to the chloride-containing carbon has a methyl group, the next following methylene is now a
carbonyl, and the next following methylene is an oxygen.

O H O
C
H 3
R O R
O O
Syndiotactic H H
H C O H C
3
3

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