Chemistry Reference
In-Depth Information
1-16 Draw projection diagrams (planar zigzag) for
(a) the syndiotactic polymer produced by 1,2 enchainment of isoprene.
(b) isotactic poly(3,4-isoprene).
1-17
Polyethylene and polyisobutene are both hydrocarbon polymers and have
intermolecular forces of similar magnitude. Yet one polymer is a plastic
and fiber-former and the other is an elastomer. Comment briefly on the
reason for this difference in properties.
1-18
Poly(vinyl alcohol) is made by free-radical polymerization of vinyl acetate
and subsequent base-catalyzed transesterification with methanol to yield
the alcohol polymer.
(a) Write an equation showing the transesterification of one repeating unit
of poly(vinyl acetate) to one of poly(vinyl alcohol).
(b) Before the advent of nuclear magnetic resonance spectroscopy, one
way of determining head-to-head structures in poly(vinyl alcohol) was
by means of the following difference in diol reactions:
H
H
H
H
HIO
4
(1,2 DIOL)
C
C
C+
C
Solution
OH
OH
O
O
H
H
HIO
4
(1,3 DIOL)
C
CH
C
C
No reation
Solution
OH
OH
With a particular poly(vinyl alcohol) sample no periodic acid is con-
sumed, within the limits of analytical accuracy. This indicates no apparent
(1,2-diol) cleavage. However, the viscosity average molecular weight of
the sample decreased from 250,000 to 100,000. Explain these results in
terms of the structures of poly(vinyl acetate) and poly(vinyl alcohol). [The
analytical technique is described by P. J. Flory and F. S. Leutner,
J. Polym. Sci. 3, 880 (1948); 5, 267 (1950).]
1-19
Polyethylene terephthalate (1-5) is a crystallizable polymer which is
melted and shaped at temperatures greater than 270
C because of its high
crystal melting point. It was thought that substitution of propylene glycol
for the ethylene glycol in reaction (1-1) would produce a polyester that
would still be crystallizable and hence rigid, but would also be processable
at lower temperatures because of the increased hydrocarbon character of
the polymer backbone. Should the glycol used here be 1,3-propane diol or
the 1,2-isomer? Justify your answer briefly.
