New insights into the effects of molecular weight and end group on the temperature-induced phase transition of poly(N-isopropylacrylamide) in water  

作　　者：QIU XingPing KOGA Tsuyoshi TANAKA Fumihiko WINNIK Fran oiseM. 

机构地区：[1]Department of Chemistry and Faculty of Pharmacy,University of Montreal,CP 6128 Succursale Centre Ville,Montreal,QC H3C 3J7,Canada [2]Department of Polymer Chemistry,Graduate School of Engineering,Kyoto University,Katsura,Kyoto 615-8510,Japan [3]Institute of Theoretical Polymer Science (ITPS) 5-19-2 Ozenji,Asao-ku,Kawasaki 615-8510,Japan [4]World Premier International (WPI) Research Center Initiative,International Center for Materials Nanoarchitectonics (MANA) and National Institute for Materials Science (NIMS),1-1 Namiki,Tsukuba 305-0044,Japan

出　　处：《Science China Chemistry》2013年第1期56-64,共9页中国科学（化学英文版）

基　　金：supported by a grant of the Natural Sciences and Engineering Council of Canada;by a FY2009 Japan Society for the Promotion of Science Invitation Fellowship Program for Research in Japan(Long-term)

摘　　要：In an attempt to clarify issues related to the molecular weight dependence of the phase transition of poly(N-isopropylacrylamide) (PNIPAM) in water,we prepared a library of PNIPAM samples of well-controlled molecular weight (7000 to 45000 g/mol) bearing identical groups on each chain end.The polymers were synthesized by reversible addition-fragmentation chain transfer (RAFT) polymerization of N-isopropylacrylamide (NIPAM) with a bifunctional chain tranfer agent and further end group modification.The effects of the end group chemical structure,hydroxyethyl (HE),propargyl (Pr),chloroethyl (CE),n-butyl (nBu),n-hexyl (nHe),and isobutylsulfanylthiosulfanyl (IBS) on the phase transition temperature of aqueous PNIPAM solutions were investigated by high-sensitivity differential scanning calorimetry (HS-DSC),yielding the enthalpy ΔH and the endotherm maximum temperature (T M),and turbidimetry,providing the cloud point (T CP) of each solution.The T CP and T M of the PNIPAM sample of lowest molar mass (M n 7,000 g/mol,0.5 g/L) ranged,respectively,from 38.8 to 22.5 °C and 42.2 to 26.0 °C,depending on the structure of the end-group,whereas H showed no strong end-group dependence.The phase transition of all polymers,except,-di(n-butyl-PNIPAM),exhibited a marked dependence on the polymer molar mass.In an attempt to clarify issues related to the molecular weight dependence of the phase transition of poly（N-isopropylacrylamide） （PNIPAM） in water,we prepared a library of PNIPAM samples of well-controlled molecular weight （7000 to 45000 g/mol） bearing identical groups on each chain end.The polymers were synthesized by reversible addition-fragmentation chain transfer （RAFT） polymerization of N-isopropylacrylamide （NIPAM） with a bifunctional chain tranfer agent and further end group modification.The effects of the end group chemical structure,hydroxyethyl （HE）,propargyl （Pr）,chloroethyl （CE）,n-butyl （nBu）,n-hexyl （nHe）,and isobutylsulfanylthiosulfanyl （IBS） on the phase transition temperature of aqueous PNIPAM solutions were investigated by high-sensitivity differential scanning calorimetry （HS-DSC）,yielding the enthalpy ΔH and the endotherm maximum temperature （T M）,and turbidimetry,providing the cloud point （T CP） of each solution.The T CP and T M of the PNIPAM sample of lowest molar mass （M n 7,000 g/mol,0.5 g/L） ranged,respectively,from 38.8 to 22.5 °C and 42.2 to 26.0 °C,depending on the structure of the end-group,whereas H showed no strong end-group dependence.The phase transition of all polymers,except,-di（n-butyl-PNIPAM）,exhibited a marked dependence on the polymer molar mass.

关 键 词：poly（N-isopropylacrylamide） phase transition temperature high-sensitivity differential scanning calorimetry TURBIDIMETRY end group effect 

分 类 号：O633.22[理学—高分子化学] TQ174.756[理学—化学]