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Novel Y-shaped block copolymers of poly(ethylene glycol) and poly(N-isopropylacrylamide),PEG-b-(PNIPAM)_2,were successfully synthesized through atom transfer radical polymerization(ATRP).A difunctional macroinitiator was prepared by esterification of 2,2-dichloroacetyl chloride with poly(ethylene glycol) monomethyl ether(PEG).The copolymers were obtained via the ATRP of N-isopropylacrylamide(NIPAM) at 30℃with CuCl/Me_6TREN as a catalyst system and DMF/H_2O(v/v = 3:1) mixture as solvent.The resulting copolymers were characterized by gel permeation chromatography(GPC) and ~1H NMR.These block copolymers show controllable molecular weights and narrow molecular weight distributions(PDI<1.15).Their phase transition temperatures and the corresponding enthalpy changes in aqueous solution were measured by differential scanning calorimetry(DSC).As a result,the phase transition temperature of PEG_(45)-b-(PNIPAM_(55))_2 is higher than that of PNIPAM,however, the corresponding enthalpy change is much lower,indicating the significant influence of the macromolecular composition and architecture on the phase transition.
Novel Y-shaped block copolymers of poly (ethylene glycol) and poly (N-isopropylacrylamide), PEG-b- (PNIPAM) _2, were synthesized synthetically through atom transfer radical polymerization (ATRP). A difunctional macroinitiator was prepared by esterification of 2 , 2-dichloroacetyl chloride with poly (ethylene glycol) monomethyl ether (PEG). The copolymers were obtained via the ATRP of N-isopropylacrylamide (NIPAM) at 30 ° C with CuCl / Me_6TREN as a catalyst system and DMF / H_2O = 3: 1) mixture as solvent. The resulting copolymers were characterized by gel permeation chromatography (GPC) and ~ 1H NMR. The block copolymers show controllable molecular weights and narrow molecular weight distributions (PDI <1.15). Their phase transition temperatures and the corresponding enthalpy changes in aqueous solution were measured by differential scanning calorimetry (DSC). As a result, the phase transition temperature of PEG_ (45) -b- (PNIPAM_ (55)) _2 is higher than that of PNIPAM, enthalpy change is much lower, indicating the significant influence of the macromolecular composition and architecture on the phase transition.