Vinylphosphonic Acid Homo- and Block Copolymers

Vinylphosphonic acid homo- and block copolymers with styrene have been prepared via anionic polymerization of dialkylvinylphosphonates (VPE) and subsequent hydrolysis of the precursor polyester with trimethylsilylbromide. Poly(vinylphosphonic acid) (PVPA) homopolymers with 4200<<(M)over bar>(w)<814000 have been obtained with vinyl-diisopropyl-phosphonate as monomer. With polystyryl anion as macroinitiator, AB block copolymers have been obtained with block compositions from approximately 9:2 to 3:7; however, the total molecular weights are limited to <10000, due to solubility limitations. H-1 DOSY NMR has been used to prove a real block-type structure consisting of hydrophobic polystyrene and hydrophilic PVPA (PVPA-b-PS), which exhibits a phase-separated morphology. It was found that the bulk proton conductivity does not change significantly with different molecular weights of the homopolymers, but is strongly dependant on the composition of the block copolymers. PVPA-b-PS with low PS content, behaves more or less like PVPA homopolymers, whereas PVPA-b-PS with a high PS content looses its conductivity when heated above the glass transition temperature of the PS phase. The swelling behaviour of the block copolymers differs significantly from that of PVPA homopolymers, when exposed to a humidified environment.