Soluble poly(N-isopropylacrylamide-co-3-(trimethoxysilyl)propyl methacrylate), P(PNIPAAm-co-TMSPMA, copolymers with broad composition range, possessing condition and composition dependent LCST-type behavior, are successfully synthesized. Due to the hydrophobic character of the TMSPMA moieties, both the cloud point (TCP) and clearing point (TCL) decrease with increasing TMSPMA content, from 34.3 °C to 23.4 °C for the poly(N-isopropylacrylamide) homopolymer and copolymer with 11.1 mol% TMSPMA, respectively. Unexpected heating-cooling hysteresis with loss of transparency is found in the case of copolymers with higher TMSPMA contents due to in situ sol-gel cross-linking without any catalyst above the cloud point, which can be utilized for obtaining new smart hybrid materials. The copolymers possess closely the same, relatively high thermal and thermooxidative stabilities as that of PNIPAAm.

Poly(N-isopropylacrylamide-co-3-(trimethoxysilyl)propyl methacrylate), P(NIPAAm-co-TMSPMA), copolymers with relatively high TMSPMA contents without insoluble fraction are successfully synthesized. Subsequent sol-gel reactions in both the absence and presence of tetraethyl orthosilicate lead to gels with high gel fractions. The resulting gels undergo gel collapse at 28.6-28.7 °C, i.e., below that of poly(N-isopropylacrylamide) homopolymer of 34.3 °C. Unexpectedly, the theophylline-loaded hybrid gels release the drug not only below but also above the gel collapse temperature (GCT) with considerable rates and released amounts of drug. Surprisingly, evaluation of the sustained release profiles by the Korsmeyer-Peppas equation indicates that the release occurs by Fickian diffusion above GCT, which can be attributed to the lack of significant drug-polymer interaction at such temperatures. These results can be widely applied for the design and utilization of TMSPMA-based sol-gel polymer hybrids with desired release profiles of solutes below and above GCT for a variety of applications.

SYNOPSISThe present status and future aspects of polymerization of ethylene and of propylene are reviewed. Main emphasis is directed towards catalyst development, but the general features of some new polymerization processes are also described.