SYNTHESIS OF POROUS HYDROGELS OF NIPAM COPOLYMER BY REVERSIBLE ADDITION FRAGMENTATION CHAIN TRANSFER PHOTOPOLYMERIZATION

The macro-CTA (chain transfer agent) of poly(N,N'-dimethylacrylamide) (PDMAM) containing trithiocarbonate groups was prepared by reversible addition fragmentation chain transfer (RAFT) polymerization. And then it reacted with N-isopropyl acrylamide (NIPAM) and N,N'-methylene-bisacylamide (BIS) to prepare the PNIPAM-g-PDMAM comb hydrogels with different lengths and contents of the grafted chains at 20 degrees C. The porous comb hydrogels were prepare by using poly (ethylene glycol) (PEG4000) as a pore-forming agent. The structure of the hydrogels was characterized by FTIR (Fourier transform infrared spectrometer) and SEM (scanning electron microscope). The photos of SEM indicated that comparing with conventional hydrogels,the porous comb dydrogles with loose structure had a distinctive porous characteristic. The mechanism of hydrogels synthesis and the effects of the grafted chains and porous structure on the properties of hydrogels were discussed. Experimental results showed that the grafted chains significantly affected the properties of nonporous hydrogels, including swelling ratio, deswelling rate and LCST (lower critical solution temperature). Though the deswelling rate decreased, the grafted chains had no effect on the swelling ratio of the porous comb hydrogels. The formation of a porous structure has been shown to effectively enhance the deswelling rate of PNIPAM hydrogels without grafting chains, but it didn't change the LCST.