Chemistry Reference
In-Depth Information
Grafting Efficiency
ð
GE
Þð
%
Þ
Weight of polymer grafted
Weight of polymer grafted
¼
Weight of homopolymer
100
þ
¼ W
1
W
0
½
W
1
W
0
þW
2
=
½
100
(2.24)
where
W
1
,
W
0
, and
W
2
are the weights of the cellulose graft copolymer, the original
cellulose, and the homopolymer, respectively. The weight of homopolymer (
W
2
)
can be calculated by subtracting the amount of grafted polymer plus the amount of
unreacted monomer from the initial amount of monomer. The amount of monomer
remaining without reacting after grafting can be determined by volumetric method
(bromide-bromate method) [
102
] or by spectrophotometric methods.
Naturally, the GP (%) and GE (%) values given above are apparent or crude
values, and they do not indicate the true values since they are calculated for the
mixture consisting of true graft copolymer and the non-grafted cellulose. In some
papers [
100
], the true values, for example, true grafting percentage (GP
T
%) which
is the weight ratio of grafted polymer to true-grafted polymer, have also been
determined after separating the non-grafted cellulose from the apparent cellulose
graft copolymer.
2.3.2 Molecular Weight of Grafted Polymer Chains and the
Frequency of Grafting
The molecular weight of graft chains is determined generally by viscometric
method [
39
-
41
,
76
,
101
], by gel permeation chromatography (GPC) [
30
], and by
1
H-NMR spectroscopy after separating the graft chains from the graft copolymer,
i.e., by hydrolyzing the cellulose backbone of graft copolymer using 72 % H
2
SO
4
[
100
]. Grafting frequency (
G
F
) is defined as the number of grafted polymer chains
(
N
g
) per chain of cellulose [
39
,
101
,
103
].
ðN
g
Þ :
Molecular weigth of cellulose
Molecular weigth of graft copolymer
Number of grafts per cellulose chain
(2.25)
Grafting percentage
100
When the grafting process occurs mainly on the surface of the cellulose back-
bone, in other words the grafting is performed in heterogeneous medium, the
number of grafted polymer chains per cellulose chain is in the range of unity, and
it rarely exceeds the unity [
104
]. In addition, the molecular weight of graft chains
may be in the order of 10
5
[
7
]. Nishioka and Kosai [
41
] reported that in homoge-
neous grafting carried out in dimethyl sulfoxide-paraformaldehyde (DMSO-PF)
