Effects of micelle structures formed in selective solvents on crystallization behaviors of poly(ethylene glycol)-b-poly(styrene) copolymers
Effects of micelle structures formed in selective solvents on crystallization behaviors of poly(ethylene glycol)-b-poly(styrene) copolymers
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DOI：
10.1016/j.polymer.2007.03.023
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发表时间：
2007-04
期刊：
影响因子：
4.6
通讯作者：
Yan-Feng Chen;Fengbo Zhang;Xu-Ming Xie;Jinying Yuan
中科院分区：
文献类型：
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作者：
Yan-Feng Chen;Fengbo Zhang;Xu-Ming Xie;Jinying Yuan
采用原子转移自由基聚合（ATRP）方法合成了结构明确的两亲性嵌段共聚物聚乙二醇甲醚-b-聚苯乙烯（mPEG-b-PS），其中PS嵌段具有不同的分子量。通过对嵌段引入选择性溶剂，结晶和无定形嵌段在溶液中自组装成不同的胶束结构。原子力显微镜（AFM）被用来表征胶束结构。据观察，球形胶束总是形成，而层状聚集体只出现在PS-选择性溶剂时，在mPEG-b-PS中的PS块的分子量低。可结晶的mPEG块自组装成形成的胶束的核心或冠。利用差示扫描量热仪（DSC）研究了自组装结构对mPEG嵌段结晶行为的影响。结果表明，当PS分子量远大于mPEG分子量时，mPEG嵌段在胶束冠部结晶时的结晶度低于在胶束核部结晶时的结晶度。在这种情况下，当mPEG嵌段在胶束冠中结晶时，不溶性PS嵌段形成的胶束核心非常大，因此mPEG链必须稀疏地分布在胶束冠中。同一胶束内或不同胶束间的mPEG链很难聚集在一起结晶。但当PS分子量低于mPEG分子量时，由于不溶性PS形成的核较小，mPEG分子链在胶束冠中容易聚集结晶，mPEG分子链在胶束冠中结晶时的结晶度较高。
Well-defined amphiphilic block copolymers, poly(ethylene glycol) methyl ether-b-poly(styrene) (mPEG-b-PS), in which the PS blocks had different molecular weights, were synthesized by atom transfer radical polymerization (ATRP). Through introduction of selective solvents for the blocks, crystalline and amorphous blocks were self-assembled into different micelle structures in solutions. Atomic force microscopy (AFM) was used to characterize the micelle structures. It was observed that spherical micelles were always formed, whereas lamellar aggregates appeared only in the PS-selective solvent when the molecular weight of the PS block in mPEG-b-PS was low. The crystallizable mPEG blocks were self-assembled into either the core or corona of the micelles formed. The effects of the self-assembled structures on the crystallization behavior of mPEG blocks were then investigated with differential scanning calorimeter (DSC). When the PS molecular weight was much larger than that of mPEG, the result showed that the crystallinity of the mPEG block was lower when mPEG blocks crystallized in the corona than that in the core of the micelles. In this case, when mPEG blocks crystallized in micelle coronae, the micelle core formed by insoluble PS blocks was very big, so mPEG chains had to distribute sparsely in the micelle coronae. It was hard for mPEG chains in one micelle or among different micelles to gather together to crystallize. However, when the PS molecular weight was lower than that of mPEG, the crystallinity of mPEG was higher when the mPEG chains crystallized in the micelle corona, as the core formed by insoluble PS was small and the mPEG chains in the corona were easy to aggregate and crystallize.