Chemistry Reference
In-Depth Information
y
x
n
O
O
m
ethyl methacrylate styrene
unit
unit
A copolymer can also be linear or branched. Should there be regularity in the repetition of the
structural units and should this repetition alternate, then the copolymer is called an
alternating
copolymer
. An absence of such regularity would make it a
random copolymer
.
An example of an alternating copolymer can be a copolymer of styrene with maleic anhydride:
n
O
O
O
In addition to the random-sequence and an alternating one, sometimes called ordered-sequence,
there are also
block copolymers
. These are copolymers made up of blocks of individual polymers
joined by covalent bonds. An example can be a block copolymer of styrene and isoprene:
m
n
polystyrene block-polyisoprene block
Still another type of a copolymer is one that possesses backbones composed of one individual
polymer and the branches from another one. It is called a
graft copolymer,
because many such
materials were formed by grafting the branch polymers to the polymer backbone. This, however, is
not always the case and many graft copolymers were formed by polymerizing the branch copolymer
from a different polymer backbone. (The subject of block and graft copolymers is discussed in
Chap.
9
) A graft copolymer of polyacrylonitrile on polyethylene can serve as an example:
CN
CN
CN
CN
In both block and graft copolymers the length of the uninterrupted sequences may vary.
