Limited Fraction of Crystallized Side Chains in Bottlebrush Poly(n-alkyl methacrylate)s  

作　　者：Ming-Yue Xiang Dong Lyu Ling-Zhi Liu Yong-Feng Men 

机构地区：[1]State Key Laboratory of Polymer Physics and Chemistry,Changchun Institute of Applied Chemistry,Chinese Academy of Sciences,Changchun 130022,China [2]School of Applied Chemistry and Engineering,University of Science and Technology of China,Hefei 230026,China

出　　处：《Chinese Journal of Polymer Science》2021年第9期1211-1216,共6页高分子科学（英文版）

基　　金：This work was finandaily supported by the National Natural Science Foundation of China(No.51525305).

摘　　要：Crystallinity of bottlebrush polymers due to side chain crystallization has been considered to be related to the length of the side chains only under the assumption of complete participation of crystallization by all sidechains.Recent experimental results revealed that in poly(n-alkyl methacrylate)s a fraction of side chains could not crystallize due to constraints imposed by the trapped main chain entanglements and required expansi on of main chain-main chain distanee.This result renders the original simplified con sideration of the origin of crystallinity in bottlebrush polymers questionable.In this work,we introduce a new parameter f_(c),the fraction of crystallizable side chains,to better describe the crystallinity of bottlebrush polymers.A lin earrelati on ship between the meltingenthalpy and the number of alkyl groups in side chains for bottlebrush polymers reported repeatedly indicates that f_(c) remains essentially unchanged when bottlebrush polymers had the same main chain structure and grafting degree but different side chain lengths.The slope of the above-mentioned linear relationship is thus △H_(CH2)xf_(c),where △H_(CH2) stands for the melting enthalpy of one mole alkyl group packed into the crystal.With a known value of f_(c),it is possible to estimate the value of △H_(CH_(2)).In case of poly(n-alkyl methacrylate)s,we estimated △H_(CH_(2)) of hexagonal crystal being at most 5.74 kJ/mol with the knowledge of possibly smallest f_(c) of 0.67 obtained from small angle X-ray scattering data.Therefore,the crystallinity of bottlebrush polymer would be calculated based on the equati on X_(c)=f_(c)×N_(c)/N with N and N_(c) being the nu mber of alkyl groups in a side chain and those packed in the crystalline structure,respectively.Both chemical structure and grafting degree of bottlebrush polymers affect f_(c).

关 键 词：Poly(n-alkyl methacrylate)s(PMA(n)s) PMA(n)-co-PMMA Crystallization behavior The fraction of crystallizable side chain(fc) Grafting degree(G) 

分 类 号：TQ317[化学工程—高聚物工业]