SURFACE-REACTION OF POLY[BIS(TRIFLUOROETHOXY)PHOSPHAZENE] FILMS BY BASIC HYDROLYSIS

A novel surface reaction of a fluoroalkoxyphosphazene polymer is reported. Films of poly[bis(trifluoroethoxy)phosphazene], [NP(OCH2CF3)2]n, underwent surface hydrolysis when treated for 0-15 min with 8 M aqueous sodium hydroxide in the presence of 0.05 M tetra-n-butylammonium bromide as a phase-transfer agent. This reaction converted a hydrophobic surface to one with hydrophilic and adhesive character. No surface reaction by NaOH solutions was detected in the absence of Bu4NBr. On the basis of a series of surface analytical data, the principle chemical reaction was found to be a replacement of P-OCH2CF3 side groups at the polymer surface by P-O-NBu4+ units. The modified surfaces were found to possess anionic sites, since an exchange reaction with the cationic dye methylene blue took place readily at the surface. No exchange occurred with the anionic dye Biebrich scarlet. Microscopic examination of the dyed films allowed the depth of the surface reaction to be measured. Contact-angle analysis showed that the surface of the polymer became progressively more hydrophilic as the reaction progressed. No significant changes in surface texture were detected. Surface reactions were also carried out with a commercial mixed-substituent fluoroalkoxyphosphazene elastomer. After extensive surface hydrolysis, films of [NP-(OCH2CF3)2]n retained their solubility in organic solvents, in which they were analyzed by P-31, C-13, H-1, and F-19 NMR spectroscopy. The NMR analysis also suggested the presence of -O-NBu4+ units. GPC analysis of an extensively modified material indicated that some cleavage of the phosphazene backbone may have occurred. The hydrolysis process was monitored by the reaction of solutions of [NP(OCH2CF3)2]n with NaOH in the presence of Bu4NBr in refluxing THF. The mechanism of adhesion is discussed.