Synthesis of Soluble Phosphate Polymers by RAFT and Their In Vitro Mineralization

Abstract

Soluble linear (non-crossed linked) poly(monoacryloxyethyl phosphate) (PMAEP) and poly(2-(methacryloyloxy)ethyl phosphate) (PMOEP) have been successfully synthesised through reversible addition fragmentation chain transfer (RAFT) mediated polymerization. Our findings indicate diene impurities are the cause of crosslinking initially and this suggests that crosslinking can be prevented to a low chain length. Block copolymers consisting of PMAEP or PMOEP and poly(2-(acetoacetoxy) ethyl methacrylate) PAAEMA were successfully prepared and were immobilised on aminated slides. Simulated body fluid studies revealed that calcium phosphate (CaP) minerals formed on both the soluble polymers and their gels were very similar. Both the PMAEP polymers and the PMOEP gel showed a CaP layer most probably brushite or monetite based on the Ca/P ratios. A secondary CaP mineral growth with a typical hydroxyapatite (HAP) globular morphology was found on the PMOEP gel. The soluble-PMOEP film formed carbonated HAP according to Fourier transform infrared (FTIR) spectroscopy. Block copolymers attached to aminated slides showed only patchy mineralization, possibly due to the ionic interaction of negatively charged phosphate groups and protonated amines.