Chemistry Reference
In-Depth Information
The vinyl acetate content of such materials ranges between 3% and 40%, and the
copolymers are more soluble and pliable than poly(vinyl chloride) homopolymer.
They can be shaped mechanically at lower temperatures than homopolymers with the
same degree of polymerization and are used mainly in surface coatings and products
where exceptional flow and reproduction of details of a mold surface are needed.
The term random copolymer is retained here because it is widely used in poly-
mer technology. A better term in general is statistical copolymer. These are pri-
marily copolymers that are produced by simultaneous polymerization of a
mixture of two or more comonomers. They include alternating copolymers,
described below, as well as random copolymers, which refer, strictly speaking, to
materials in which the probability of finding a given monomer residue at any
given site depends only on the relative proportion of that comonomer in the reac-
tion mixture. The reader will find the two terms used interchangeably in the tech-
nical literature, but they are distinguished in more academic publications.
1.5.2
Alternating Copolymer
In an alternating copolymer each monomer of one type is joined to monomers of
a second type. An example is the product made by free-radical polymerization of
equimolar quantities of styrene and maleic anhydride:
H
H
H
H
H
H
H
CH
2
C
C
C
CH
2
C
C
C
CH
2
C
C
C
C
C
OOO
OOO
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These low-molecular-weight polymers have a variety of special uses including
the improvement of pigment dispersions in paint formulations.
1.5.3
Graft Copolymer
Graft copolymers are formed by growing one polymer as branches on another pre-
formed macromolecule. If the respective monomer residues are coded A and B,
the structure of a segment of a graft copolymer would be
BBBBBBB
A
A
A
A
BBBBB
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