Probing the Two-Stage Transition upon Crossing the Glass Transition of Polystyrene by Solid-State NMR
作者：Yongjin Peng, Chenting Cai, Rongchun Zhang, et al.
關(guān)鍵字：glass transition, polystyrene, heterogeneous dynamics, solid-state NMR
論文來(lái)源：期刊
具體來(lái)源：Chinese Journal of Polymer Science 2016, 34, 446-456
發(fā)表時(shí)間：2016年
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-1H dipolar couplings based Double
Quantum-Filtered (DQF) and dipolar filter (DF) experiment 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 experiment provided the evidence for second stage
transition during which the time scale of molecular motions changed from very
slow (t>ms) to very fast (t<μs).
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).