Probing the Two-stage Transition upon Crossing the Glass Transition of Polystyrene by Solid-state NMR  

作　　者：Yong-jin Peng Chen-ting Cai Rong-chun Zhang Tie-hong Chen 孙平川 李宝会 Xiao-liang Wang Gi Xue An-Chang Shi 

机构地区：[1]School of Physics, Nankai University, Tianjin 300071, China [2]Key Laboratory of Functional Polymer Materials of Ministry of Education and College of Chemistry, Nankai University and Collaborative Innovation Center of Chemical Science and Engineering, Tianjin 300071, China [3]Department of Polymer Science and Engineering, The School of Chemistry and Chemical Engineering, State Key Laboratory of Coordination Chemistry, Nanjing University, Nanjing 210093, China [4]Department of Physics and Astronomy, McMaster University, Hamilton, Ontario L8S 4M1, Canada

出　　处：《Chinese Journal of Polymer Science》2016年第4期446-456,共11页高分子科学（英文版）

基　　金：financially supported by the National Science Fund for Distinguished Young Scholars(No.20825416);the National Natural Science Foundation of China(No.21374051);973 program(No.2012CB821503);PCSIRT(No.IRT1257);CERS-1-61.A.C.S.acknowledges the support of the Natural Science and Engineering Council(NSERC)of Canada

摘　　要：A two-stage transition upon crossing the glass transition of polystyrene with increasing temperature was precisely determined and interpreted by using solid-state nuclear magnetic resonance （SSNMR）, 1H-XH dipolar couplings based double quantum-filtered （DQF） and dipolar filter （DF） experiments and 13C chemical shift anisotropy （CSA） based centerband-only detection of exchange （CODEX） experiment are used to fully characterize the time scale of molecular motions during the glass transition. While differential scanning calorimetry （DSC） and CODEX experiment predicted the first stage of glass transiton, DQF and DF experiments provided the evidence for the second stage transition during which the time scale of molecular motions changed from very slow （t 〉 ms） to very fast （t 〈 Its）. The first stage of glass transition begins with the occurrence of remarkable slow re-orientation motions of the polymer backbone segments and ends when the degree of slow motion reaches maximum. The onset and endpoint of the conventional calorimetric glass transition of polystyrene can be quantitatively determined at the molecular level by SSNMR. In the second stage, a subsequent dramatic transition associated with the melting of the glassy components was observed. In this stage liquid-like NMR signals appeared and rapidly increased in intensity after a characteristic temperature Tf （-1.1Tg）. The signals associated with the glassy components completely disappeared at another characteristic temperature Tc （-1.2Tg）.A two-stage transition upon crossing the glass transition of polystyrene with increasing temperature was precisely determined and interpreted by using solid-state nuclear magnetic resonance （SSNMR）, 1H-XH dipolar couplings based double quantum-filtered （DQF） and dipolar filter （DF） experiments and 13C chemical shift anisotropy （CSA） based centerband-only detection of exchange （CODEX） experiment are used to fully characterize the time scale of molecular motions during the glass transition. While differential scanning calorimetry （DSC） and CODEX experiment predicted the first stage of glass transiton, DQF and DF experiments provided the evidence for the second stage transition during which the time scale of molecular motions changed from very slow （t 〉 ms） to very fast （t 〈 Its）. The first stage of glass transition begins with the occurrence of remarkable slow re-orientation motions of the polymer backbone segments and ends when the degree of slow motion reaches maximum. The onset and endpoint of the conventional calorimetric glass transition of polystyrene can be quantitatively determined at the molecular level by SSNMR. In the second stage, a subsequent dramatic transition associated with the melting of the glassy components was observed. In this stage liquid-like NMR signals appeared and rapidly increased in intensity after a characteristic temperature Tf （-1.1Tg）. The signals associated with the glassy components completely disappeared at another characteristic temperature Tc （-1.2Tg）.

关 键 词：Glass transition POLYSTYRENE Heterogeneous dynamics Solid-state NMR. 

分 类 号：O632.12[理学—高分子化学] O657.2[理学—化学]