Chemistry Reference
In-Depth Information
CH
2
O
CH
2
OH
CH
2
Cl
CH
2
O
CHO
O
R
CH
2
O
O
n
Fig.
8
.9
Benzyloxy and
polyethyleneglycol spacers.
O
O
X
n
Y
OO
Fig.
8
.10
Spacers introduced by
Friedel-Crafts grafting.
Br
2.7 Polyvinylpyridines
thermal polymerisation of cyclotri(dichlorophos-
phazene) into poly(dichlorophosphazene) [58-60];
this material contains only nitrogen and phosphorus
atoms in the main chain and a very high content of
>PCl
2
units (Fig. 8.16). With respect to other poly-
mers, there are many more starting points for func-
tionalisation: the very electrophilic chlorine atoms
allow a series of subsequent substitutions to give a
large number of different side groups.
Both 2- and 4-vinylpyridines can copolymerise with
DVB under the same conditions as for styrene to give
similar cross-linked bead-shaped materials. They are
available now on the market and can be modified
into several reagents [49-52]; those made from the
4-isomer are more reactive (Fig. 8.14).
2.8 Polybenzimidazoles
2.10 Chlorofluoropolymers
These insoluble homopolymers are not cross-linked;
they are obtained by thermal polycondensation of
phthalic acid with tetraaminobiphenyls (Fig. 8.15).
The resulting material is processed to give porous
beads or fibres, exhibits a high thermal stability and
is resistant to oxidation. This inertness has made the
chemical modifications more difficult, but several
examples are known [53-57].
With the exception of Nafion
TM
, polyhalogenated
polymers are of limited value due to the absence of
porosity and the difficulty in performing surface
graftings. However, when a limited degree of func-
tionalisation is required, which can be the case in
catalysis with organometallic complexes, it is pos-
sible to introduce specific groups such as hydroxyls,
carbonyls, carboxyls and amines at the surface of
chlorofluoropolymers (PTFE, PVF
2
) by a substitution
reaction [61] of the halogens under strongly basic
conditions.
2.9 Polyphosphazenes
These linear homopolymers are obtained by the
