CuSO4-环己酮氧化还原体系的自由基聚合引发能力

研究了CuSO4-环己酮(CyH)氧化还原体系引发甲基丙烯酸甲酯(MMA)的普通自由基聚合。结果显示,当n(CuSO4)∶n(CyH)=1∶5~1∶200,反应温度在70℃~90℃时反应均可进行,所得聚合物分子量在单体低转化率时已较高,且随单体转化率的增长没有明显变化,符合普通自由基聚合的特征,证实了该体系的氧化还原引发能力。另外还研究了以CuSO4-CyH-CuBr2/络合物引发MMA的反向原子转移自由基聚合,所得聚合物的分子量随转化率的上升而增加,但可控性较差。初步分析聚合机理为:Cu2+将CyH羰基α位的-CH2-氧化成了-C.H-自由基,引发单体聚合。此结果意味着过渡金属离子存在时CyH不能作为聚合溶剂。

Redox Initiation of CuSO4-Cyclohexanone in Radical Polymerization

Using CuSO4-cyclohexanone redox as initiator,the radical polymerization of methyl methacrylate was briefly investigated.The results show that the polymerization of methyl methacrylate could proceed under the molar ratio of CuSO4 to cyclohexanone from 1∶5 to 1∶200 and the reaction temperature of 70 ℃～90 ℃.The polymer achieves high molecular weight at low conversion and remains a constant during the whole reaction processing,maintains the characteristic of the conventional radical polymerization.The reverse atom transfer radical polymerization of MMA initiated by CuSO4-cyclohexanone redox was also investigated.The molecular weight of polymer increases with the monomer conversion,but the controllability is rather limited.The mechanism was assumed to be that the alpha-CH2-of cyclohexanone(Cα-H) was oxidized to radical-C·H-(Cα·) by Cu2+,which then initiated the chain propagation.The results imply that the cyclohexanone cannot be used as the solvent in the radical polymerization of electron-deficient vinyl momomers such as acrylates and acrylamides in the presence of oxidizing agents.