Fundamentals of Materials Science and Engineering: An Integrated Approach, 3e

GTBL042-04 GTBL042-Callister-v2 September 26, 2007 1:46

2nd Revise Page

4.8 Molecular Configurations • 113

represent bonds that project out of the plane of the page, dashed ones represent bonds

that project into the page.^8

syndiotactic In asyndiotactic configuration, the R groups alternate sides of the chain:^9

configuration

R H HH

HHHHHHHH

CCCCC

CCCC

R R HHR R

and for random positioning

VMSE

Stereo and

Geometrical

Isomers

Syndiotactic

R H R H H

HHHHHHHH

CCCCC

CCCC

RR H H R

the termatactic configurationis used.^10

atactic configuration

VMSE

Stereo and

Geometrical

Isomers

Atactic

Conversion from one stereoisomer to another (e.g., isotactic to syndiotactic) is

not possible by a simple rotation about single chain bonds; these bonds must first be

severed and then, after the appropriate rotation, they are reformed.

In reality, a specific polymer does not exhibit just one of these configurations;

the predominant form depends on the method of synthesis.

Geometrical Isomerism

Other important chain configurations, or geometrical isomers, are possible within

repeat units having a double bond between chain carbon atoms. Bonded to each of

the carbon atoms participating in the double bond is a side group, which may be

(^8) The isotactic configuration is sometimes represented using the following linear (i.e.,
nonzigzag) and two-dimensional schematic:
C
HH
H
C C
HH
H
C
R R R
C
H
H
C C
HHH
H
C
R
H
C
R
(^9) The linear and two-dimensional schematic for syndiotactic is represented as
C
HH
H
C C
H
HH
C
R
R R
R
C
H
H
C C
HH
HH
C
H
C
R
(^10) For atactic the linear and two-dimensional schematic is
C
HHH
H
C C
H
C
R
R R
R
C
HHH
C C
HHH
HH
C C
R