New Understanding on the Memory Effect of Crystallized iPP  

作　　者：Xiang-yang Li Zhe Ma Feng-mei Su Nan Tian You-xin Ji Jie Lu Zhen Wang 李良彬 

机构地区：[1]National Synchrotron Radiation Laboratory, College of Nuclear Science and Technology, University of Science and Technology of China [2]Department of Mechanical Engineering, Eindhoven University of Technology, P.O. Box 513, 5600MB, Eindhoven, The Netherlands [3]Department of Polymer Science and Engineering, CAS Key Lab of Soft Matter Chemistry, University of Science and Technology of China

出　　处：《Chinese Journal of Polymer Science》2014年第9期1224-1233,共10页高分子科学（英文版）

基　　金：financially supported by the China Postdoctoral Science Foundation(No.2012M521233);the Fundamental Research Funds for the Central Universities(WK2310000031);the National Natural Science Foundation of China(Nos.51033004,51227801,51303166);National Natural Science Funds for Distinguished Young Scholars(No.51325301);the 973 program of MOST(2010CB934504);supported by the Opening Project of Soochow University Biomedical Polymers Laboratory and the Jiangsu Key Laboratory of Advanced Functional Polymer Design and Application(Soochow University)

摘　　要：In this study, recovery processes of isotactic polypropylene （iPP） melted spherulites at 135 ℃ after melting at higher temperatures （170 ℃-176 ℃） were investigated with polarized optical microscopy and Fourier transform infrared spectroscopy. The recovery temperature was fixed to exclude the interference from heterogeneous nuclei. After melting at temperatures between 170 ℃ and 174 ℃, the melted spherulite could recover back to the origin spberulite at low temperatures. Interestingly, a distinct infrared spectrum from iPP melt and crystal was observed in the early stage of recovery process after melting at low temperatures, where only IR bands resulting from short helices with 12 monomers or less can be seen, which indicates that the presence of crystal residues is not the necessary condition for the polymer memory effect. Avrami analysis further indicated that crystallization mainly took place in melted lamellae. After melting at higher temperatures, melted spherulite cannot recover. Based on above findings, it is proposed that the memory effect can be mainly ascribed to melted lamellae, during which crystalline order is lost but conformational order still exists. These conformational ordered segments formed aggregates, which can play as nucleation precursors at low temperatures.In this study, recovery processes of isotactic polypropylene （iPP） melted spherulites at 135 ℃ after melting at higher temperatures （170 ℃-176 ℃） were investigated with polarized optical microscopy and Fourier transform infrared spectroscopy. The recovery temperature was fixed to exclude the interference from heterogeneous nuclei. After melting at temperatures between 170 ℃ and 174 ℃, the melted spherulite could recover back to the origin spberulite at low temperatures. Interestingly, a distinct infrared spectrum from iPP melt and crystal was observed in the early stage of recovery process after melting at low temperatures, where only IR bands resulting from short helices with 12 monomers or less can be seen, which indicates that the presence of crystal residues is not the necessary condition for the polymer memory effect. Avrami analysis further indicated that crystallization mainly took place in melted lamellae. After melting at higher temperatures, melted spherulite cannot recover. Based on above findings, it is proposed that the memory effect can be mainly ascribed to melted lamellae, during which crystalline order is lost but conformational order still exists. These conformational ordered segments formed aggregates, which can play as nucleation precursors at low temperatures.

关 键 词：Memory effect Isotactic polypropylene Conformational ordering Topological connectivity Aggregate. 

分 类 号：O632.12[理学—高分子化学]