writer：Haili Wang, Yiyang Zhou, Huagao Fang, Yu Li, Pei Xu, Yunsheng Ding and Zhigang Wang
keywords：聚乳酸，离子液体，接枝，结晶动力学
source：期刊
specific source：Acta Polymerica Sinica, 2016, 11, 1606-1614
Issue time：2016年

Polylactide (PLA) underwent molecular degradation when it was exposed to gamma ray radiation, and the degradation was inhibited somehow in the presence of 1-allyl 3-methylimidazolium chloride (AMIMCl). The grafting reaction of AMIMCl on PLA chains occurred during the irradiation to obtain imidazolium cations grafted PLA (PLA-IM). The molecular masses and the contents of end groups of the resultant PLA samples were measured by gel permeation chromatography (GPC) and nuclear magnetic resonance (¹H-NMR), respectively. Compared with the PLA sample irradiated without AMIMCl (PLA-S), PLA-IM possessed less hydroxyl end groups and higher molecular mass (3 times as high as that of PLA-S). The nucleation and growth of crystalline during isothermal crystallization process were observed using polarized optical microscopy (POM). The results revealed that PLA-IM possessed spherulitic morphology which was same as other PLA samples, and the growth rate of spherulites was mainly dependent on the molecular mass of PLA samples, demonstrating highest growth rate for PLA-S, followed by PLA-IM and lowest for PLA-L at the same crystallization temperature. However, different from PLA-L and PLA-S, PLA-IM showed increased nucleation density in the whole experimental temperature range due to the presence of grafted imidazolium cations on PLA chains. Isothermal crystallization kinetics for the PLA samples was then investigated by differential scanning calorimetry (DSC) and analyzed using Avrami equation. The results showed that the crystallization rate of PLA-IM had improved obviously because of its higher nucleation density. When the isothermal crystallization temperature was higher than 125 ^oC, the half crystallization time of PLA-IM was shorter than that of PLA-S with lower molecular mass. Different from the retardant effect of ionic liquids (ILs) on PLA nucleation in PLA/ILs blends, the ionic interaction between the imidazolium cations grafted on PLA chains facilitates the orderly arrangement of PLA chains and formation of nuclei in the crystallization process, which contributes to the acceleration of crystallization kinetics.