Biomedical Engineering Reference
In-Depth Information
Table 10.1
Examples of active groups or molecules for organic-inorganic
hybridization.
Active groups
Molecule
Glycidoxy (epoxy)
Glycidoxypropyl trimethoxysilane (GPTMS)
Methacryl
Methacryloxypropyl trimethoxysilane,
CH
2
=
C(CH
3
)COCO(CH
2
)
3
-Si(OCH
3
)
3
-Si(OCH
3
)
3
(
γ
-MPS)
(iso)Cyano
3-Isocyanatotriethoxysilane,
O
=
C
=
N-(CH
2
)
3
-Si(OC
2
H
5
)
3
Vinyl trimethoxysilane, CH
2
=
CH-Si(OCH
3
)
3
(VTMS)
Vinyl
Allyl trimethoxysilane, CH
2
=
CHCH
2
-Si(OCH
3
)
3
Allyl
Amino
Aminotripropyl triethoxysilane,
NH
2
(CH
2
)
3
-Si(OCH
3
)
3
(APTS)
-SH
Mercaptopropyl trimethoxysilane,
HS(CH
2
)
3
-Si(OCH
3
)
3
(MPTMS)
Mercaptopropyl triethoxysilane,
HS(CH
2
)
3
-Si(OC
2
H
5
)
3
(MPTES)
PDMS itself can be considered a hybrid. PDMS is synthesized by con-
densation between organic silanes that have typical formula R
4-
n
-SiX
n
(X can be a halogen or another functional group that gives HO-Si
and R is an organic group) and the species HO-M in Equation 10.1.
One of the products of high-molecular-weight PDMS is silicone rubber.
Vapor-phase condensation proceeds with the halo-silanes even under
ambient conditions, since the Si-X group is very reactive. Its reactivity
is illustrated by fumes evolving when SiCl
4
is in contact with the air: it
is hydrolyzed with the humidity in the atmosphere to form nanometer-
sized SiO
2
particles (fume) with HCl as the by-product. TiCl
4
gives TiO
2
in a similar way. This means that Si-X groups are readily hydrolyzed to
yield Si-OH, and the halo-silane is susceptible to indirect condensation
with the HO-M under aqueous conditions. Direct condensation also
takes place between two alkoxysilanes (R
4-
n
Si(-OR
)
n
):
Si-OR
+
R
O-Si
R
-O-R
>
<
→
>
Si-O-Si
<
+
(10.3)
This condensation requires higher temperature or an active catalyst.
R
2
Si(OR)
2
is a candidate to be involved in the hydrolysis and conden-
sation. (CH
3
)
2
Si(OH)
2
is a hydrolysis product of (CH
3
)
2
SiCl
2
, whose
polycondensation leads to poly(dimethylsiloxane), [-Si(CH
3
)
2
-O-].