Biomedical Engineering Reference
In-Depth Information
PP
poly(propylene)
PPO
poly(propylene oxide)
PS
poly(styrene)
PTFE
poly(tetrafluoroethylene)
PTMO
poly(tetramethylene oxide)
PU
poly(urethane)
PVP
poly(vinylpyridine)
RTV
room temperature vulcanization
SEC
size exclusion chromatography
SEM
scanning electron microscopy
STPV
silicon thermoplastic vulcanizate
TEM
transmission electron microscopy
TEOS
tetraethoxysilane
TPE
thermoplastic elastomer
TPU
thermoplastic poly(urethane)
TPV
thermoplastic vulcanizate
VTES
vinyltriethoxysilane,
XPS
X-ray photoelectron spectroscopy
1
Introduction
The great variety of available monomers combined with extensive research
studies in the field of copolymerization allow us to access many advanced
technical polymers and copolymers. Hence, it is possible to combine the
properties of different homopolymers either to combine the different char-
acteristics or to overcome a particular drawback of one of the homopolymer
components. The blending of homopolymers is another rapidly growing tech-
niquewithmuchpotential.Itsmainadvantage lies in the fact it employs sim-
ple processes that are attractive economically and are less time-consuming.
The blending of polymers involves some quite different concepts than those
in copolymerization. Whereas covalent bonds hold together copolymer com-
ponents, the homopolymers of a blend are held together by chemical and/or
physical interactions. Since for most common polymers these are weak Van
der Waals forces, the miscibility is usually not thermodynamically favourable.
This is especially true in the case of silicone polymers since the constitutive
(OSi(Me)
2
) units do not permit the establishment of strong interactions with
the other polymer. A widespread method used to decrease the interfacial ten-
sion consists of the use of copolymers as compatibilizers. These can be either
added as a preformed copolymer or synthesized in-situ. The synthesis of such
copolymers is also reviewed here because of its distinctive chemistry in the
silicone field. Besides these thermodynamical considerations, the rheologi-
cal properties of both the homopolymers and the compatibilizers as well as
the mixing process play an important role in the development of the final
blend morphology and consequently its mechanical properties. Several theor-
