Chemistry Reference
In-Depth Information
1.3.1 Concept of Graft Copolymerisation
A polymer is called copolymer when the repeating units are of two different
monomers. The sequence in which monomers attach themselves depends upon
their relative reactivities. Copolymers can be random, alternate, block and graft
copolymers. First three types of copolymers differ with respect to sequencing of
monomers. In case of random copolymer, monomer units are randomly placed
(arranged), whereas monomers are present in an ordered form in case of alternate
copolymer. Block copolymer involves the segments of different monomers
attached together at terminals. Graft copolymer has a preformed polymer acting
as a backbone to which polymeric chains are attached at different sites.
Thus, graft copolymer consists of a polymer backbone with lateral covalently
linked side chains [
46
]. The side chains may consist of a single monomer or of
binary mixture. The graft copolymerisation involving single monomer usually
occurs in a single step, whereas graft copolymerisation in the presence of vinyl
monomers binary mixtures may occur with the simultaneous or sequential addi-
tion of monomers. When two monomers are added side by side, it is called mosaic
grafting. First graft copolymer was synthesised by Alferd and Bandel in 1950 by
polymerising vinyl acetate in the presence of styrene and vinylidene chloride [
48
].
The presence of functional groups on the backbone is the basic requirement for
the synthesis of graft copolymers. Graft copolymerisation can be performed in
homogeneous as well as in heterogeneous medium depending upon the solubility
of monomer and the nature of solvent used for the reaction. Graft
copolymerisation proceeds either through “grafting from” or “grafting onto”
method.
“Grafting from” method involves the generation of active sites on the polymer
backbone which in turn initialises the monomer polymerisation onto backbone and
thereby resulting in the formation of graft copolymer as follows:
x
2
X
1
X
1
X
1
*
X
2
*
When a growing polymer chain (X
2
) attacks another polymer X
1
, the grafting is
said to occur through “grafting onto” method as follows:
X
1
X
1
*
X
2
þ n
X
2
!ð
X
2
Þ
nþ
1
