Chemistry Reference
In-Depth Information
acrylamide onto PHB was also studied.
97
The authors use three different
models (eqns (7.1), (7.2) and (7.3)) to describe the percentages of grafting
degree (W%), monomer/macromer composition (C
x
%) and crystallinity
index (CI%), respectively.
d
n
2
r
4
n
g
|
1
W %
¼
m
g
m
i
m
i
100
(7
:
1)
C
x
%
¼
m
x
m
g
100
(7
:
2)
A
lCH
3
A
lC
O
C
CI %
¼
(7
:
3)
where m
g
, m
i
and m
x
are thermogravimetric analysis (TGA) derived graft
copolymer weight, neat backbone polymer weight, and weight of the
monomer or macromer component under analysis, respectively. A
lCH3
is the
FTIR integral peak area of the band at wavelength (l) 1382 cm
1
assigned to
methyl bending vibrations, which is insensitive to the crystallinity changes,
and A
lC-O-C
is the integral peak area at 1185 cm
1
corresponding to ester
vibrations that is sensitive to changes in crystallinity.
97
In all the solvents
evaluated (acetone, methanol, ethanol, ethyl acetate and chloroform), the
researchers found that the sample grafted in chloroform had the highest
degree of grafting (
91%) in spite of the chloride radical that was reported
to terminate the reaction.
97
In addition, the chloroform-grafted sample was
found to exhibit higher water uptake, about 2.5-fold higher than the sample
grafted in acetone. This could be due to an increased degree of acrylamide
grafting as a result of higher polymer solubilization in chloroform.
97
Several
PHA modifications by gamma induced graft copolymerization have been
reviewed elsewhere.
98
Olefinic bonds of unsaturated polymers confer a cross-linking/grafting
advantage upon irradiation with ultraviolet (UV) light even in the absence
of photosensitizers or initiators.
84
On the other hand, saturated polymers
such as PHO normally need photo-initiators (e.g. benzophenone) to initiate
the cross-linking reaction upon UV irradiation.
83
A series of unsaturated
PHAs derived from linseed oil was cross-linked using UV radiation at a
wavelength of 300 nm, which resulted in modified PHAs with increased glass
transition temperatures and improved curing due to the cross-linking
reactions.
99
For biomedical applications, inhibition of protein adsorption, as well as
platelet activation and adhesion on the polymer surface, is critical to the
eciency of the material. For example, use of PHAs as artificial blood con-
tacting devices such as arteries and anticoagulant films was limited by
surface-induced thrombosis.
83,100
The adsorption of plasma proteins
and adherence of activated platelets onto the polymer surface resulted in
their transformation to pseudopods and subsequent release of platelet
biochemical content, which in turn activated other platelets leading to the
E
.
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