SYNTHESIS, CHARACTERIZATION, AND MODIFICATION OF POLY(ORGANOPHOSPHAZENES) WITH BOTH 2,2,2-TRIFLUOROETHOXY AND PHENOXY SIDE-GROUPS

High molecular weight polyphosphazenes that bear varying ratios of phe noxy and 2,2,2-trifluoroethoxy groups have been synthesized by the rea ctions of (NPCl2)n with sodium phenoxide, PhO-Na+, and sodium 2,2,2-tr ifluoroethoxide, CF3CH2O-Na+, using either competitive or sequential e xposure to the two nucleophiles. The relative amounts of NP(OCH2CF3)2, NP(OCH2CF3)(OPh), and NP(OPh)2 units in the final polymer are depende nt on both the synthesis method and the amounts of CF3CH2O-Na+ and PhO -Na+ used for the synthesis. The sequential reaction of poly(dichlorop hosphazene), (NPCl2)n, with CF3CH2O-Na+ followed by PhO-Na+ yields mix tures of polymers that have different compositions depending on the pr esence or absence of tetra-n-butylammonium bromide or 15-crown-5 ether . The reactions are complicated by the fact that phenoxy groups in NP( OCH2CF3)(OPh) units are replaced by 2,2,2-trifluoroethoxy groups at el evated temperatures or at 25-degrees-C in the presence of either 15-cr own-5 ether or tetra-n-butylammonium bromide. The sodium salt of 3-hyd roxypropanol replaces both 2,2,2-trifluoroethoxy and phenoxy groups in these polymers at room temperature in the presence of either tetra-n- butylammonium bromide or 15-crown-5 ether. These side-group exchange r eactions are affected by steric effects. The mechanisms of these react ions are interpreted from the perspective that the reaction of CF3CH2O -Na+ alone with the small-molecule model compound, (NPCl2)3, yields si gnificant amounts of geminally substituted products in the presence of either tetra-n-butylammonium bromide or 15-crown-5 ether. The T(g) of the mixed-substituent polymers increased as the fraction of phenoxy g roups in the polymer increased. For the polymers containing equal amou nts of 2,2,2-trifluoroethoxy and phenoxy groups, the polymers with the highest ratio of geminal NP(OCH2CF)2 units had the lowest T(g)'s.