Page 176 - Academic Press Encyclopedia of Physical Science and Technology 3rd Polymer

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Encyclopedia of Physical Science and Technology en012i-947 July 26, 2001 11:11

684 Polymers, Inorganic and Organometallic

The ability to alter pendant substituents and control lar interactions in the more polar C OorS O bonds. The
MW, polydispersity, solubility, polymer architecture, and MW of the thionyl polymers, determined from light scat-
copolymer composition gives versatility to polyphosp- tering, range from 5000 to 140 000 with polydispersities
hazenes. The polymers can vary from elastomers to ce- from 1.4 to 2.3 depending on the substituents. The combi-
ramics, from hydrophobic to hydrophilic, from bioactive nation of low T g and high oxygen diffusion coefficient for
to bioinert, and from electrical conductor to insulator. In some of these polymers has led to applications as matri-
addition, many of these polymers have low T g values (e.g., ces for pressure and phosphorescence sensor composites
◦
T g ([Cl 2 PN] n ) =−63 C) that result in rubbery behavior at in the aerospace industry.
fairly low temperatures.
3. Other Phosphorus-Containing Polymers
2. Poly(carbophosphazene)
Oligomers and polymers of elemental phosphorus were
and Poly(thiophosphazene)
mentioned previously (Section II). Although they are
The backbone of the polyphosphazene chain can be rather sensitive toward atmospheric oxygen and moisture,
modified by insertion of heteroatoms such as car- in small quantities they have applications as fire retar-
bon [poly(carbophosphazene)] or sulfur [poly(thio- dants, surface treatment of metals for coatings, and in ion-
phosphazene)]. These polymers are obtained by heating exchange resins. Oligomers and polymers of phosphorus
5−
the heterocyclic trimer analogs that are prepared by a with oxygen [P 4 O 6 , P 4 O 10 , P 8 O 16 , (PO) , P 3 O , P 6 O 6−
n
12
8
n−
3 + 3 cocondensation reaction as illustrated in Fig. 21. and (PO 3 ) ] are well known. Several examples are given
n
Unless the poly(thiophosphazene) has bulky sidegroups, it in Fig. 23. The small neutral P O and P S compounds
is hydrolytically unstable. However, if the oxidation state have polyhedral cage structures. (PO 3 ) n− polymers, how-
n
of sulfur is increased to VI [poly(thionylphosphazene), ever, are composed of orthophosphate (phosphoanhy-
Fig. 22], the polymer is stable to atmospheric moisture. dride) residues in which n may be several multiples of
Moreover, only the halogens on P undergo substitution 10 to several hundred. These macromolecules are con-
with NaOR (R = phenyl). stituent parts of all living cells and are responsible for
An interesting feature of these polymers is the increase cellular energy transfer and other biochemical processes.
in T g relative to [R 2 PN] n . This suggests that the presence Phosphorus–sulfur oligomers (P 4 S x , x = 3, 5, 7, 9, 10)
of carbon or sulfur significantly reduces chain mobility are also known.
and flexibility presumably because of the higher rotational Aromatic polyphosphates that are prepared from phos-
barrier in C N and S N and the increase in intermolecu- phodichloridates and aromatic diols [Eq. (24)] possess the

FIGURE 21 Synthesis of poly(carbophosphazene) and poly(thiophosphazene).