α-二亚胺镍(Ⅱ)催化甲基丙烯酸甲酯聚合

以4种不同结构的α-二亚胺镍(Ⅱ)催化剂(t-Bu)—N CH—CH N—(t-Bu)]NiBr₂(C1), C₆H₅—N C(Me)—C(Me) N—C₆H₅]NiBr₂(C2), (2,6-C₆H₃(Me)₂)—N C(Me)—C·(Me) N—(2,6-C₆H₃(Me)₂)]NiBr₂(C3)和(2,6-C₆H₃(i-Pr)₂)—N C(An)—C(An) N—(2,6-C₆H₃(i-Pr)₂)]NiBr₂(An=acenaphthyl)(C4), 在甲基铝氧烷(MAO)作用下, 对甲基丙烯酸甲酯(MMA)进行催化聚合. 以C2为模型催化剂系统研究了Al/Ni摩尔比、 单体浓度、 聚合温度、 聚合时间和反应溶剂对催化活性及聚合物分子量的影响. 在较适合的聚合条件(催化剂用量为1.6 μmol, Al/Ni摩尔比为800, MMA浓度为2.9 mol/L, 甲苯为溶剂, 聚合温度为 60 ℃, 聚合时间为4 h)下, 讨论了催化剂结构对催化活性和聚合物分子量的影响. 研究发现, 催化剂C1~C3催化MMA聚合均得到富含间规结构的聚甲基丙烯酸甲酯(PMMA). 催化剂结构中空间位阻增大导致催化活性降低, 空间位阻最小的 C1催化活性最高达107.8 kg/(mol Ni·h)]; 而空间位阻最大的C4催化活性仅为7.8 kg/(mol Ni·h). 催化剂结构中给电子效应增加有利于催化活性及聚合物分子量的增加. C2催化活性为62.5 kg/(mol Ni·h), 所得聚合物的分子量为5.0×10⁴; 而具有较强给电子效应的C3催化活性达到96.9 kg/(mol Ni·h), 并得到更高分子量的聚合物(7.6×10⁴).

Polymerization of Methyl Methacrylate with α-Diimine Nickel(Ⅱ)†

Four α-diimine nickel(Ⅱ) complexes: (t-Bu)—NCH—CHN—(t-Bu)]NiBr₂(C1), C₆H₅—NC(Me—C(Me) N—C₆H₅]NiBr₂(C2), (2,6-C₆H₃(Me)₂)—NC(Me)—C·(Me) N—(2,6-C₆H₃(Me)₂)]NiBr₂(C3) and (2,6-C₆H₃(i-Pr)₂)—NC(An)—C(An) N—(2,6-C₆H₃(i-Pr)₂)]NiBr₂(An=acenaphthyl)(C4), in the presence of methylaluminoxane(MAO) as cocatalyst, were applied in the polymerization of methyl mathacrylate(MMA). The influence of polymerization parameters, such as molar ratio of Al/Ni, monomer concentration, polymerization temperature and time, as well solvents were studied with complex C2/MAO system. Based on these results, all nickel complexes were compared under optimized polymerization conditions{1.6 μmol catalyst, n(Al)/n(Ni)=800, MMA]=2.9 mol/L, toluene as solvent, 60 ℃ for 4 h}. In each case, syndiotactic enriched polymer was obtained. The complexes with more bulky frame work exhibit lower catalytic activities, for example, C1 with the smallest bulky frame work gives the highest activity, 107.8 kg/(mol Ni·h) while C4 with the biggest bulky frame work gives the lowest activity, 7.8 kg/(mol Ni·h); The complexes with more electronic donor substituents exhibit higher activities and molecular weight of PMMA. The activity of C2 is 62.5 kg/(mol Ni·h), and the molecular weight of PMMA is 5.0×10⁴, while that of C3 is 96.9 kg/(mol Ni·h) and produce higher molecular weight of PMMA(7.6×10⁴).