Synthesis of soluble phosphate polymers by RAFT and their in vitro mineralization

Soluble linear (non-cross-linked) poly(monoacryloxyethyl phosphate) (PMAEP) and poly(2-(methacryloyloxy)ethyl phosphate) (PMOEP) were successfully synthesized through reversible addition-fragmentation chain transfer (RAFT)-mediated polymerization and by keeping the molecular weight below 20 K. Above this molecular weight, insoluble (cross-linked) polymers were observed, postulated to be due to residual diene (cross-linkable) monomers formed during purification of the monomers, MOEP and MAEP. Block copolymers consisting of PMAEP or PMOEP and poly(2-(acetoacetoxy) ethyl methacrylate) (PAAEMA) were successfully prepared and were immobilized on aminated slides. Simulated body fluid studies revealed that calcium phosphate (CaP) minerals formed on both the soluble polymers and the cross-linked 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.