Chemistry Reference
In-Depth Information
Alkyl, aryl, alkoxy, and aminocyclotriphosphazenes fail to polymerize. This is believed to be due
to an absence of easily ionizable halogen to phosphorus bonds. At the same time, materials that
presumably facilitate ionization of the phosphorus to halogen bonds, such as water, carboxylic acids,
and metals, accelerate the polymerization [
173
].
The all-inorganic polymer decomposes readily at elevated temperatures and is very sensitive to
hydrolytic attack. Quantitative replacements of the halogen groups, however, are possible with
alkoxy, aryloxy, alkyl, aryl, or amino groups to yield much more stable materials. The replacements
are achieved by refluxing the inorganic polymer in an ether solvent for several hours with sodium
alkoxide or aryloxide, a metal alkyl, or aryl, or with a primary or a secondary amine. Of particular
interest are substitutions with fluoroalkoxy groups, like the following:
Cl
OCH
2
C
3
F
7
THF
+
2n C
3
F
7
H
2
O Na
N
P
N
P
n
n
Cl
OCH
2
C
3
F
7
Mixed fluoroalkoxy compounds can be used to obtain a variety of properties. The materials find
application as elastomers, because they exhibit good chemical resistance and good thermal stability.
In addition, many retain the useful elastomeric properties at low temperature. As a result, among other
applications, they are attractive for use as sealants and as fuel lines in arctic environment.
Phosphonitrile polymers are self-extinguishing or fire retardant. This led to the development of
flame- and heat-resistant polyimide composites that are prepared from maleimide-substituted
phosphazenes [
231
,
232
]. The maleimide group is used for cross-linking. The substituted
phosphazene can be illustrated as follows:
O
O
N
O
P
N
P
O
O
O
N
P
N
N
O
O
O
O
A deferent approach to the synthesis of polyphosphazenes was reported [
179
]. It is based on
condensation of suitable Si-N-P precursors:
R
R
Δ
Si
N
P
X
NP
-(CJ
3
)
3
SiX
R'
R'
where, R,R
0
¼
OCH
2
CF
3
, O-Ph.
In this preparation, the desired substituents are introduced before the polymerization. The resultant
polymers [
179
] are soluble in various solvents. Their molecular weight distributions vary from 1.4 to
3.5 and
alkyl, aryl; X
¼
M
w
from 50,000-150,000.
