New hydrolysis-dependent thermosensitive polymer for an injectable degradable system.

Novel, bioerodible, thermosensitive poly(NIPAAm-co-dimethyl-gamma-butyrolactone acrylate), with a hydrolysis-dependent thermosensitivity, was synthesized by radical polymerization with a varying dimethyl-gamma-butyrolactone acrylate (DBA) content, and the properties of the copolymers were characterized using differential scanning calorimetry, gel permeation chromatography in conjunction with static light scattering, Fourier transform infrared spectroscopy (FTIR), nuclear magnetic resonance (NMR), and acid titration. The lower critical solution temperature of the copolymers decreases with increasing DBA content, but then increases after ring-opening hydrolysis of the DBA side group. FTIR and NMR spectra showed the copolymerization of these two monomers and the hydrolysis-dependent ring-opening of the DBA side group. It was also found that there are no low-molecular-weight byproducts but rather dissolution of the polymer chains at 37 degrees C during the time frame of application. Models of the kinetics suggest that the hydrolysis reaction is self-catalytic due to an increase in hydrophilicity and charge, and thus accessible water concentration, caused by ring-opening of the DBA.