Y-shaped block copolymers of poly(ethylene glycol) and poly(N-isopropylacrylamide) synthesized by ATRP

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/Me₆TREN as a catalyst system and DMF/H ₂ O (v/v=3:1)n 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.