碳二亚胺调控下甲基丙烯酸甲酯的可逆-失活自由基聚合

Reversible-deactivation Radical Polymerization of Methyl Methacrylate Mediated by Carbodiimide Catalysts

首次采用2种碳二亚胺(二环己基碳二亚胺(DCC)和N,N′-二异丙基碳二亚胺(DIC))作为催化剂、碘(I2)与偶氮二异庚腈(ABVN)原位生成烷基碘化物为引发剂,实现了甲基丙烯酸甲酯(MMA)的可逆-失活自由基聚合.首先,对比了2种催化剂对该体系催化活性的大小,发现DCC作为催化剂时对聚合的可控程度优于DIC.然后详细考察了DCC用量、引发剂用量和不同溶剂对聚合反应的影响.结果表明,在反向碘转移聚合(RITP)的基础之上添加DCC或DIC,均可以有效降低聚合物的分子量多分散指数(PDI=M_w/M_n).[MMA]_0:[I_2]_0:[ABVN]_0:[DCC]_0=200:1:1.7:4时具有最佳的可控效果,凝胶渗透色谱(GPC)测定的分子量与理论分子量吻合,且数均分子量随转化率增加呈线性增长,分子量多分散指数较小(PDI <1.26).在甲苯、苯、四氢呋喃(THF)、苯甲醚4种溶剂中均有很好的可控聚合特征.最后,通过~1H-NMR对所得聚合物结构进行表征,证明为碘原子封端,端基保有度达到97.5%,并成功进行了聚甲基丙烯甲酯的扩链反应;通过自由基捕捉实验、紫外等对碳二亚胺调控MMA聚合的机理进行了讨论.

The reversible-deactivation radical polymerization（RDRP） of methyl methacrylate（MMA） was carried out utilizing an alkyl iodide in situ formed as initiator and dicyclohexylcarbodiimide（DCC） or N,N′-diisopropylcarbodiimide（DIC） as highly efficient organic catalysts for the first time. Firstly, the catalytic activity of the two catalysts was demonstrated and compared. The control of the polymerization by DCC was better than that by DIC under the same experimental conditions. Then the influence of the amount of catalyst DCC, the amount of traditional initiators and the type of solvents on the polymerization was investigated in detail. The results show that the addition of DCC or DIC catalyst can effectively reduce the polydispersity index（PDI =Mw/Mn）, as compared with the reverse iodine chain transfer polymerization（RITP）. The catalytic performance is excellent with the ratio of [MMA]0：[I2]0：[ABVN]0：[DCC]0 = 200：1：1.7：4. The measured molecular weight by GPC is consistent with the theoretical molecular weight, and the molecular weight increases linearly with the increase in conversion rate. The molecular weight polydispersity index is small（PDI 1.26）. The polymerizations of MMA in different solvents were carried out. The induction period is shortened and the polymerization rate is increased with the increase of catalyst or initiator amount. The polymerizations have good control effect in toluene, benzene,tetrahydrofuran（THF）, anisole. The structure and the iodine-end-capped structure of the obtained PMMA was demonstrated by ~1H-NMR spectrum. The calculated Mn,NMR was in good agreement with Mn,GPC, and the fraction of iodine chain end of the PMMA chains was up to 97.5%, and the iodine terminus could be efficiently reactivated for chain extension. Last, the mechanism of the polymerization mediated by carbodiimide is discussed based on free radical trapping experiments and ultraviolet absorption. The high conversion of CP-I to CPo radical catalyzed by DIC and the complexation peak of I2/carbodiimide detected by ultraviolet absorption spectroscopy demonstrate that the polymerization catalyzed by carbodiimide proceeds according to the reversible complexation mediated polymerization mechanism.