The polymorphic transition of trans-1,4-polyisoprene (TPI) during stretching was investigated by in situ wide-angle X-ray diffraction and Fourier transform infrared spectroscopy.The influences of the initial structure,stretching temperature,and strain rate on the contents of different crystal modifications (α,β) were explored.The results confirm that the α-β transition occurs during stretching of TPI that only contains α crystal (α-TPI).When the stress is relaxed,the β crystal formed during stretching remains,which indicates that the transition is irreversible.On the other hand,stretching of TPI that only contains β crystal (β-TPI) results in orientated β crystal.No β-α transition occurs during stretching.The different structures of stretched α-TPI and β-TPI exclude the previously proposed "melting-recrystallization mechanism".The α-β transition depends significantly on temperature and strain rate,indicating the transition is governed both by thermodynamics and kinetics.Our results support a solid-solid transition mechanism rather than a melting-recrystallization mechanism.The irreversible nature of the transition is attributed to the metastability of the β phase in the unstretched state.Different from the "β phases" that appear in polymers with stress-induced reversible transitions,e.g.poly(butylene terephthalate) and poly(butylene succinate),the stability of β phase in TPI is high that can be long-lived.The strain rate dependence of α-β transition hinders the determination of critical stress for the transition.It further indicates that the local stress within the sample is more heterogeneous at higher strain rates.

Chun-Bo Zhang;Lei Wang;Bo Yang;Hui Zhao;Guo-Ming Liu;Du-Jin Wang

Shenzhen Key Laboratory of Polymer Science and Technology,College of Materials Science and Engineering,Shenzhen University,Shenzhen 518060,China;CAS Key Laboratory of Engineering Plastics,Beijing National Laboratory for Molecular Sciences,Institute of Chemistry,Chinese Academy of Sciences,Beijing 100190,China;University of Chinese Academy of Sciences,Beijing 100049,China;School of Materials Science & Engineering,Beijing Institute of Fashion Technology,Beijing 100029,China

高分子科学（英文版）

[1]Chun-Bo Zhang;Lei Wang;Bo Yang;Hui Zhao;Guo-Ming Liu;Du-Jin Wang-.Stress-induced Solid-Solid Crystal Transition in Trans-1,4-polyisoprene)[J].高分子科学（英文版）,2022(03):256-265

polyisoprene,unstretched

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