Crystallization and Tensile Deformation Mechanism of Propylene/Ethylene Copolymers in α and γ Polymorphs

Jiayi Zhao1, Yingying Sun2, and Yongfeng Men1

1State Key Laboratory of Polymer Physics and Chemistry, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, University of Chinese Academy of Sciences, Renmin Street 5625, 130022 Changchun, P.R.China
2ExxonMobil Asia Pacific Research & Development Co., Ltd, 1099 Zixing Road, Minhang District, 200241 Shanghai, P.R.China

Isotactic polypropylene (iPP) is a widely used commercial polymer with various polymorphs. γ-form, which can only crystallize at high pressure for isotactic polypropylene, is a usual polymorph for propylene copolymers. The subsequent crystallization behavior during cooling for copolymer initially in pure α-form and γ-form processed at different melt temperature has been studied [1]. Specifically, sample initially in α-form led to higher fraction of γ-form (fγ) and onset crystallization temperature (Tonset) than that of sample in γ-form under low melted temperature, which was caused by the difference between morphology of samples previously in α-form and γ-form.
Tensile deformation properties of the propylene/ethylene copolymers were also studied [2, 3]. The influence of stretching temperature and content of co-unit in transition behavior from γ-form to α-form during stretching was investigated. The critical stress for the polymorph transition was obtained which depends strongly on the stretching temperature and content of co-unit. The critical stress was higher for sample with lower co-unit content with less partitioning of ethylene co-unit in propylene crystalline lattices.
This work is supported by NSFC (21134006, 51525305) and ExxonMobil.

[1] Zhao, J.; Sun, Y.; Men, Y. Ind. Eng. Chem. Res. 56, 198 (2017). (link)
[2] Zhao, J.; Sun, Y.; Men, Y. Macromolecules 49, 609 (2016). (link)
[3] Zhao, J.; Sun, Y.; Men, Y. Submitted.