Polyphosphazenes Containing Vitamin Substituents: Synthesis, Characterization, and Hydrolytic Sensitivity

Novel polyphosphazenes containing various vitamin substituents were synthesized and characterized, and their sensitivity to hydrolysis and pH behavior was investigated. Vitamins L-1, E, and B-6 were used because of their biocompatibility, their importance in a variety of biological functions, and their potential to increase the mechanical properties of the resulting polymers, thus making these materials promising candidates for hard tissue engineering scaffolds. Chlorine replacement reactions were carried out initially with the small molecule, hexachlorocyclotriphosphazene, as a model for high polymeric poly(dichlorophosphazene). Because of the steric hindrance generated by vitamin E as a substituent, co-substituted polymers were synthesized with either glycine ethyl ester or sodium ethoxide as the second substituent Similarly, vitamin B-6 was co-substituted with glycine ethyl ester or phenylalanine ethyl ester to favor biodegradability. To prevent cross linking via multifunctional reagents, the hydroxyl groups in vitamin B-6 were protected and subsequently deprotected under acidic conditions after side group linkage to the polymer backbone. The glass transition temperatures of the polymers ranged from -24.0 to 44.0 degrees C. Hydrolysis of the polymers in deionized water at 37 degrees C was used as an initial estimate of their hydrolytic sensitivity. Different solid polymers underwent 10-100% weight loss in 6 weeks with the generation of a broad pH range of similar to 2.5-9. The weight loss during preliminary hydrolysis experiments was attributed to cleavage of the polymer backbone and/or the polymers becoming soluble in the aqueous media. during hydrolytic reactions.