Biomedical Engineering Reference
In-Depth Information
which a poly(urethane-
co
-dimethylsiloxane) block copolymer was added as
a compatibilizer for the two phases. A battery of tests (DMA, SEM, stress-
strain measurements) showed an enhancement of the semi-IPN properties
for 0.5 to 2 wt % amounts of added copolymer. For higher concentrations,
the mechanical properties diminished compared to those of the unmodi-
fied network. This is due to the fact that the additive acts like a plasticizer.
Vlad et al. [151] used a polyalkylene oxide grafted PDMS to compatibi-
lize a PU/PDMS IPN but its influence was not clearly pointed out. Gross
et al. [133] added an ethylene-methylacrylate-glycidyl methacrylate terpoly-
mer to a PBT/PDMS blend which may act as a compatibilizer.
4.2.5.2
Grafted Compatibilizer
Gornowicz [135] grafted a fluorocarbon resin (e.g. either a homo- or co-
polymer of VDF) with siloxane to enhance its compatibility with PDMS. For
example, vinyl triethoxysilane was first grafted onto fluorocarbon resin using
peroxide. Then, an added silicone phase was vulcanizated via hydrosilylation.
4.2.5.3
Branched Semi-IPNs
Xiao et al. [152] prepared a PU/PDMS semi-IPN by crosslinking into the
PU component a hydroxy-terminated PDMS bearing an amine function
such as 3-aminopropyltriethoxysilane with a trialkoxysilane and dibutyltindi-
laurate. Unfortunately, the system appeared to be phase separated. Simi-
larly, Morin [153] studied a polyamide/PDMS semi-IPN. A vinyl-containing
polysiloxane was mixed with a polyamide. Then, a hybrid-containing sili-
cone bearing epoxy functions was added to the blend to crosslink the silicone
phase. The epoxy groups act as a reactive coupling agent with the PA phase.
A semi-IPN of this grafted PDMS with Nylon 6,6 exhibited enhanced proper-
ties.
4.2.5.4
Hybrid Semi-IPNs
Hydrosilylation can also be carried out between a silicone elastomer and
a non-silicone one to yield a hybrid IPN. Arkles [154] worked with such a sys-
tem: the silicone containing hydride groups and the unsaturations supplied
by polymers such as polybutadiene or copolymers of butadiene. These hy-
brid systems do not perform as well as siloxane semi-IPNs due to the fact that
silicone is partially lost.
Finally, it should be pointed out that hydrosilylation crosslinking during
melt mixing is so efficient that many thermoplastic elastomers where a sec-
