Combine Reversible Addition Fragmentation Chain Transfer Polymerization And Click Chemistry To Prepare Thermosensitive Hydrogel

Temperature-sensitive hydrogels show prospective applications in many aspects due to its superior conventional hydrogel gel caused concern of researchers. A typic al monomer, N-isopropylacrylamide(NIPA), attracts significant attention because the lower critical solution temperature(LCST) of NIPA is close to body temperature. In this paper,different functionalized PNIPA polymers were prepared by reversible addition-fragmentation chain transfer polymerization(RAFT). Then they were used to prepare PNIPA hydrogels by Click chemistry. The main contents are listed as follows:(1)The L-PNIPA was prepared by RAFT polymerization, using 1, 4-phenylenebis(methylene) dipropyl dicarbonotrithioate(DPB) as the chain transfer agent. The end-groups of L-PNIPA were modified to prepare alkynyl-terminated L-PNIPA, which was crosslinked by pentaery thritoltriazoacetate(TAPE) to prepare hydrogels by Click chemistry. We synthesize L-PNIPA successfully with different molecular weight.It was characterized using NMR, infrared spectroscopy, gel permeation chromatography, UV and so on. Because of its small molecular weight, it has not been successful with azide crosslinking agent of small molecules though gel reaction and Click reaction..(2)The alkynyl-terminated L-PNIPA was successfully prepared by RAFT polymerization with a alkynyl-ended chain transfer agent(BDP. At the same time, GMA was copolymerized with NIPA by RAFT polymerization, gaining PNIPA copolymer containg glycidyl groups, which was azidized by sodium azide to prepare azido-PNIPA. The alkynyl-terminated L-PNIPA was reacted with azido-PNIPA by Click chemistry to prepare two series of hydrogels. The uniform network structure of the hydrogel was confirmed by SEM. Then with the increase of the degree of crosslinking or the decrease of the molecular weight of L-PNIPA, the mesh density increases and pore size becomes smaller. The equilibrium water content of gel at room temperature reduces and water loss rate and the water uptake rate are also reduced. On the other hand, the LCST of the Click gel are much lower than those of the common gel. Characterization methods is same to the first part. This method can obtain high molecular weight distribution but narrow and can ensure the controllability,and the prepared hydrogel in water loss rate, water absorption rate, and LCST has more advantages than the conventional hydrogel.(3) A star chain transfer agent(S-CTA) was synthesized successfully, which was used to prepare alkynyl-terminated S-PNIPA, which was crosslinked by azido-PNIPA to prepare hydrogels by Click chemistry. The uniform network structure of the hydrogel was confirmed by SEM. Then with the decrease of the molecular weight of L-PNIPA, the mesh density increases and pore size becomes smaller. The equilibrium water content of gel at room temperature reduces and water loss rate and the water uptake rate are also reduced. On the other hand, the LCST of the Click gel are much lower than those of the common gel. What‘s more, the equilibrium water content of the Click gel can resume after the de-swelling and re-swelling. Characterization methods is same to the first part. Compared with the conventional method, obtained theoptimization in the process, this method can obtain high molecular weight distribution but narrow and can ensure the controllability, the prepared hydrogel in water loss rate, water absorption rate, and LCST has more advantages than the conventional hydrogel.