Polyphosphazenes, effect

Anurima S, Nicholas RK, Swaminathan S, Lakshmi SN, Jacqueline LS, Paul WB, Cato TL, and Harry RA. Effect of side group chemistry on the properties of biodegradable L-alanine cosubstituted polyphosphazenes. Biomacromolecules, 2006, 7, 914-918. 

The conventional route to prepare I generally involves a high temperature melt polymerization of hexachlorocyclotriphosphazene, or trimer (IV). Recent studies have demonstrated the effectiveness of various acids and organometalllcs as catalysts for the polymerization of IV (8). Alternate routes for the preparation of chloro-polymer which do not involve the ring opening polymerization of trimer have been reported in the patent literature (9. 10). These routes involve a condensation polymerization process and may prove to be of technological importance for the preparation of low to moderate molecular weight polyphosphazenes. 

This effect has also been observed in polyphosphazenes containing alkyl- or phenyl-carborane as pendent groups.12 A typical synthetic route to poly(phenyl-carboranyl-di-trifluoroethoxy-phosphazene) having pendent phenyl-carborane groups is shown in scheme 4. A substantial improvement in the thermal stability of the polymer was observed. This is attributed to a retardation of the ring-chain de-polymerization mechanism due to steric hindrance effects of the carborane units, inhibiting helical coil formation. 

JThe effect of the substituent on the properties of the polyphosphazenes is not fully understood. For instance, [NP(OCH ) ]n and [NP C CH. homopolymers are elastomers (8,29). Synthesis using lithium, in contrast to sodium, salts is claimed to produce rubber-like fluoroalkoxyphosphazene polymers (30). The presence of unreacted chlorine or low molecular weight oligomers can affect the bulk properties (31,32). Studies with phosphazene copolymers both in solution and in the bulk state (29,33-38) indicate a rather complex structure, which points out the need for additional work on the chain structure and morphology of these polymers. 

Enough is now known about the effect of different side groups attached to a polyphosphazene chain to allow some general structure-property relationships to be understood. To a limited extent, these relationships allow the prediction of the properties of polymers not yet synthesized. Some general relationships will be described in the following sections, but specific properties associated with certain side groups are summarized in Table 3.1. 

As a coating offers increased anti-icing effectiveness and durability than fluorocarbon and silicone elastomers. These icephobic coats can reduce the accumulation of ice on products such as rooftops, aircraft, radomes, antennas, ships, and power-transmission lines. The weight of such accumulations of ice has led to aircraft crashes, fallen power lines, etc. The icephobic coats reduce the adhesive force between ice and a surface. Polyphosphazene elastomers possess these desired properties, in addition have low glass transition temperature (Tg), good environmental stability, curability, and moderate cost. 

Effect of temperature on permeability of hydrogen sulfide in a 10% H2S/CH4 gaseous mixture through various polyphosphazene membranes... 

Zumbulyadis et al. [86] selected a fluorinated polyphosphazene, containing CF3CF2CF2CF2CH2O side chains (attached to phosphorus atoms in the polymer backbone) to explore the potential of F MAS/NOESY experiments. MAS at 3.82 kHz sufficed to resolve all four F sites, though effects of isotropic indirect coupling were obscured by the linewidths. Cross peaks are seen in the two-dimensional NOESY spectrum. The authors argue that these arise from NOE processes and not from spin diffusion. 

The discussion of the behavior of eondis crystals of flexibte linear macromolecules and some of the homolc ous oUgcaners covers a witte range of cdisorder-effects and accompanying motion. For many of the macromolecules in the eondis phase chain-extension afto- erystallization with chain folding is possible [polyethylene, polytetrafluOToethylene, poly(vinylidene fluoride), polydilorotrifluoro-ethylene, some aliphatic nylons and polyphosphazenes]. Stx h extended ehain crystals are exceptionally stable and elose to equlibrium. 

Now that polymerization control has been established, these techniques may lead to cost-effective and new developments/ applications in this interesting class of polymers. Some physical properties that are sensitive to structure and chain conformations may require further investigation. Some of these polyphosphazenes are to be found among the polymers that follow. 

Dejaeger et al. (41) used a styrene-based column in THF with the addition of LiBr to minimize the polyelectrolyte effect of polytrifluoroethyoxyphosphazenes. SEC interfaced with LALLS was also tried despite low detector response caused by a low dn/dc value. The authors also demonstrated that the polyphosphazene counterparts containing no fluorine, that is, polydiphenoxy- and polyaryloxyphosphazenes, follow the universal calibration concept despite their unique backbone structure. 

---