配体骨架烷基取代基对α-二亚胺镍催化乙烯聚合的影响

ETHYLENE POLYMERIZATIONS CATALYZED BY α-DIIMINE COMPLEXES WITH DIFFERENT SUBSTITUENTS ON LIGAND BACKBONE

合成了4种α-二亚胺镍催化剂Ar—NC(R1)C(R2)N—ArNiBr2[Ar=2,6-dimethylphenyl,R1=CnH2n+1,R2=CmH2m+1;其中Cat1:m=1,n=1;Cat2:m=2,n=1;Cat3:m=3,n=1;Cat4:m=2,n=2],考察了聚合温度、催化剂浓度和催化剂配体骨架碳原子上烷基取代基对乙烯聚合反应活性、聚合物链结构和结晶性能的影响.实验发现,当配体骨架上烷基取代基R1和R2不同时,催化剂具有较高的活性,且聚合物分子量也较高;其中,Cat2和Cat3在20℃,乙烯常压和5.8mmol/L催化剂用量下,乙烯聚合活性达1.86×103kgPE/(molNi.h)和1.92×103kgPE/(molNi.h),聚合物分子量(Mw)达6.82×105和1.019×105.聚乙烯链结构分析表明,甲基支链在聚乙烯支链中占主导地位,支化度主要受反应温度的影响;同时还发现,配体骨架碳原子上烷基取代基不同的二亚胺镍催化合成聚乙烯的长支链比例相对较高,特别是在较高反应温度40℃下,己基及以上长支链比例明显增加.

Four α-diimine nickel complexes Ar-N=C （R1）C（R2 ）=N-ArNiBr2 with different alkyl substituents on backbone of ligand [ Ar = 2, 6-dimethylphenyl, R1 = Cn H2n ＋1 , R2 = Cm H2m＋1 ; Cat 1 ： m = 1, n = 1 ; Cat 2 ： m =2, n = 1; Cat 3： m = 3, n = 1; Cat 4： m = 2, n = 2] were synthesized and used to catalyze ethylene polymerization in toluene. The influences arousing from changes in alkyl substituents on the backbone carbon of the catalyst ligand on the ethylene polymerization activities, microstructures and semi-crystalline properties of polyethylene were evaluated under varied polymerization temperatures and catalyst concentrations. It was showed that the catalysts with asymmetric alkyl substituents, i. e. R1 and R2 were different, had higher activity and produced polyethylenes having higher molecular weight as compared with those with symmetric substituents. With Cat 2 and Cat 3, the ethylene polymerization activities reached 1.86 ×10^3 kg PE/（ mol Ni· h） and 1.92 ×10^3kg PE/（ mol Ni· h）, and molecular weights of polymers achieved 68.2 × 10^4 and 101.9 × 10^4 , respectively under the condition of 20℃, atmosphere and 5.8 mmol/L of catalyst concentration. Analysis of polyethylene chain structures indicated mat the main branching chain structure in polyethylene was methyl groups, and the branching degree was dependent mainly on polymerization temperature. Meanwhile, it was also showed that the polyethylene synthesized with α- diirnine nickel complexes containing diversed alkyl substituents on tigand backbone had comparatively high proportion of hexyl and longer alkyl branching chains in polymer molecules, especially for the cases when polymerization was conducted at 40 ℃.