Insight into the cryopolymerization to form a poly(N-isopropylacrylamide)/clay macroporous gel: structure and phase evolution.

The cryopolymerization and formation of a macroporous poly(N-isopropylacrylamide) (PNIPA)/clay cryogel were investigated. The mechanism of the cryopolymerization and cryogel formation was elucidated. Two processes, cryostructuration and cryopolymerization, proceed simultaneously and their relative rates determine the structure evolution and the cryogel morphology - porosity. The cryostructuration in the PNIPA/clay system during freezing, controlled by the freezing temperature and the rate of cooling, includes both water and NIPA crystallization, formation of a highly concentrated non-frozen liquid phase (NFLP) and clay aggregation. The rate of cryopolymerization and gelation is governed by the following effects: by a low polymerization temperature and after freezing, by the high cryoconcentration and a steric confinement, manifested by a reduced reagent mobility. Moreover, it depends on the cooling rate and the evolution of cryostructuration. The progress of cryostructuration and cryopolymerization during freezing was described and experimentally proved step by step. Both the phase development during freezing and the progress of cryopolymerization including gelation were monitored in situ by NMR, DSC, chemorheology and SAXS. The morphology and porosity of the cryogels were characterized by SEM and TEM.

New bioerodable thermoresponsive polymers for possible radiotherapeutic applications.

A new thermoresponsive system designed for local radiotherapy has been developed. In this system a radionuclide complex is entrapped in a thermoresponsive polymer locally precipitated at body temperature after injection of a polymer-complex solution into the tissue where a therapeutic effect is required. The lifetime of the system is controlled by the rate of polymer hydrolysis, its dissolution and elimination from the body. The thermoresponsive polymer with the cloud temperature (CT) below body temperature is based on copolymers of N-isopropylmethacrylamide with a methacrylamide-type comonomer containing hydrophobic n-alkyls of three different sizes (C(3), C(6) and C(12)) bonded by a hydrolytically labile hydrazone bond. Hydrolysis of hydrazone bond results in a copolymer soluble at body temperature. The copolymer containing 27.5 mole% of the comonomer with the C(6) moiety, which was chosen for further study, has the CT 22 degrees C and its phase separation is complete at 34 degrees C. Polymer dissolution is complete within 48 h at both pH 5.0 or 7.4. The model therapeutic radionuclide, (64)Cu, in the form of its hydrophobic chelate bis(quinolin-8-olato-N,O) [(64)Cu]copper, is efficiently kept hydrophobically entrapped in the phase-separated polymer until the dissolution by hydrolytic degradation is completed.