The Preparation, Characterization And Application Of Thermosensitive Terpolymers

Terpolymers based on N-isopropylacrylamide ( NIPAm ) , sodium 2-acrylamido -2-methyl-propanesulphonate(AMPS)and N-tert-butylacrylamide(NTBA)were synthesized by free radical copolymerization using 2,2′-azo-bis- isobutyronitrile(AIBN)as an initiator. The swelling ratios of the hydrogels at various temperatures and salt solutions were determined. The lower critical solution temperatures (LCSTs) of the linear polymer aqueous solutions were determined by measuring transmittance on UV at different temperatures. The influence of polymer concentration, polymer composition and ionic strength on LCSTs of the linear polymers was investigated. It is found that as the hydrophobic component NTBA was incorporated into the terpolymer, the LCST decreased;For the given polymer the higher the polymer concentration was, the lower the LCST was;The more NaCl was added, the more the LCST decreased; The study for LCSTs in mixed solvents of methanol and water was carried out. It was found that LCSTs of the linear polymers decreased as the content of methanol increase; while the LCST started to increase as methonal content reached to 50%(v/v) in water. When methanol achieved 60%(v/v) in water the phase transition phenomenon didn't appear;But when methanol was replaced by tetrahydrofuran or dioxane , the LCSTs of the linear polymers increased till 60% (v/v) of organic solvents in water. the phase transition phenomenon didn't appear; The hydrogels possessed both high swelling ratio and thermosensitivety. The hydrogels achieved equilibrium in short time . In hot water ( 55℃) the hydrogel started deswelling and its deswelling was a slow process. Reswelling studies indicated its repeating swelling-deswelling behavior was excellent. The hydrogels have potential applications as superabsorbents and matrixes for drug controlled release. The research of drug controlled release indicated that its effect was good and it fit enteric environment.poly(N-isopropylacrylamide) (PNIPAm) macromonomer was prepared by the chain transfer radical polymerization. Poly(Diaceton Acrylamide) -graft-poly(N-isopropylacrylamide) (PDAA-g-PNIPAm) and poly(sodium2-acrylamido-2-methyl-propanesulphonate)-graft- poly(N-vinylisobutylamide) (PAMPS-g-PNIPAm) were synthesized. Comparing the graft copolymer with the random copolymer, it is found that molecular weight of PNIPA oligomer can be controlled by using AET·HCl as the chain transfer agent. The LCSTs of the copolymers were not changed significantly compared to that of PNIPAm. The fluorescence study indicates that the Critical Micelle Concentration (CMC) of PDAA-g-PNIPAm increased as length of PNIPAm increased. As temperature is lower than LCST, the value of I1/I3 keeped certain;As temperature is higher than LCST, the value of I1/I3 decreasd with the increase of concentration ; And the higher temperature is, the CMC lower is.