Biomedical Engineering Reference
In-Depth Information
scribed in Bilgrien's patent [138] resulting in the mechanical properties and
processability of the semi-IPN being enhanced. Besides, the incorporation
of this silicone base conferred on the semi-IPN an improvement in the burn
character [139].
It is well recognized that side reactions can occur during the process
between the different compounds present in the media due to drastic environ-
ment particularly high temperatures and mechanical shearing. For example,
Fustin et al. [140] studied a melt-reacted polyester/silicone system (200
◦
C
in sealed vials). The silicone was obtained by hydrosilylation catalyzed by
Karstedt's platinum catalyst. To make the analysis easier, PBT was mimicked
by low molecular weight compounds which contained potentially reactive
groups towards the hydride group of the silicone (ester, acid, alcohol, alkene
or
-unsaturated ester). The behaviour of each group towards the hydrosi-
lane was individually studied (Fig. 11). When the hydrosilane was heated
alone, it partially reacted by itself to lead to a dimer. No reaction was observed
between the hydride-containing silicone and the ester groups. With acid (to
a minor extent) and alcohol groups, cross dehydrocoupling was observed.
The hydrosilylation reaction of the
α
,
β
-unsaturated ester and alkene were
found to be faster than cross-dehydrocoupling with the alcohol. It was found
that hydrosilylation between the hydride-functionalized silicon and the vinyl-
containing silicon was faster than any other potential side reaction. Moreover,
dimerization of the hydrosilane was found to be slower than the hydrosilyla-
tion reactions.
α
,
β
Fig. 11
Fustin et al. reactions [140]. Catalyst: Pt(0)
It should be noted that the dimerization side reaction is hugely diminished
when a radical scavenger such as Irganox 1010 is added to the medium. The
latter one of a group of convenient hindered phenol stabilizers, but thioesters
and hindered amine have also been incorporated to the blends [131].
Itoh et al. [141] patented a blend of polyurethane and silicone gum
with vinyl groups. The crosslinking reaction of the silicone component was
achieved using a radical generator. Chorvath et al. [142] also patented a sys-
tem composed of polyamide or polyester as the thermoplastic and vinyl-
containing polysiloxane cured by a peroxide or non-peroxidic initiator such
as 3,4-dimethyl-3,4-diphenylhexane (HTV). Moreover, they added different
compatibilizers such as amino-terminated or amino-grafted polysiloxane,
epoxy- or isocyanato-functionalized polysiloxane.
