混合离子液体对聚甲基丙烯酸甲酯分子链缠结及松弛行为的影响

Effect of Mixed Ionic Liquids on Chain Entanglement and Relaxation of Poly(methyl methacrylate)

首先通过两步法合成了具有双咪唑环阳离子结构的离子液体(DIL),并将其与单咪唑环离子液体(MIL)进行混合以调控黏度变化,混合离子液体(ILs)的黏度符合对数混合规则且随温度变化呈现Arrhenius型流体行为.进一步通过动态流变、示差扫描量热(DSC)、电化学测试等方法研究了混合离子液体中DIL比例对聚甲基丙烯酸甲酯(PMMA)链缠结和松弛行为的影响,并讨论了PMMA/ILs体系热稳定性、玻璃化转变及离子电导率等的变化.结果表明,DIL独特的双咪唑环结构可与PMMA分子形成更多相互作用位点,从而导致凝聚缠结的形成,很大程度上限制了PMMA分子链的运动和松弛.随DIL含量增加,PMMA/ILs体系的松弛时间、热分解温度、玻璃化转变温度等参数均呈增大趋势,但其离子电导率有所损失,这与DIL较大的分子尺寸和运动能力有关.

A kind of dicationic ionic liquid(DIL)[C8(MIM)2][TFSI]2 with double charged imidazole rings was successfully synthesized and mixed with a monocationic ionic liquids(MIL)[C8(MIM)][TFSI].Compared with MIL,the double imidazolium rings on the DIL cation greatly limits the vibration ability of the alkyl chain,which shows a much higher wavenumber in infrared spectrum.The DIL/MIL mixtures show Arrhenius fluid behaviour,and their viscosities follow the logarithmic mixing rule.With the increase of DIL content in the ILs mixtures,the viscosity and flow activation energy gradually increase,which is closely related to the molecular size and intermolecular interaction of DIL.Then,the effect of mixed ILs on the entanglement and relaxation of poly(methyl methacrylate)(PMMA)was extensively investigated by rheological tests.The master curves obtained by time-temperature superposition principle show that DIL could significantly change the relaxation behaviour and entanglement state of PMMA chains in mixed ILs.With increasing DIL content in the mixed ILs,both the terminal relaxationτ1 and entanglement relaxationτe of PMMA chains were retarded,and the entanglement network of the PMMA/ILs becomes more compact,showing higher plateau modulus and greater viscosity.More interaction sites could be formed between PMMA chains and DIL molecules due to its unique double imidazolium rings structure,which results in more cohesive entanglements among PMMA chains and thus restrict their relaxation.Moreover,there is a mathematical relationship between the rheological parameters(such asτ1 andτe)of PMMA/ILs and the viscosity of ILs mixtures,so the rheological behaviour of the system could be approximately predicted.On the other hand,thermal stability,glass transition and ion conductivity of PMMA/ILs were also discussed.The thermal decomposition temperature and glass transition temperature of PMMA/ILs increased with the DIL content,while the ionic conductivity decreased slightly.