Diimine nickel catalysis of ethylene copolymerization with polar cyclic monomers

Abstract

ε-Caprolactam (CL) and tetrahydrofuran (THF) were copolymerized with ethylene (E) and terpolymerized with E and P (propylene) for the first time made possible using the late transition metal catalyst precursor [bis(N,N ′-dimesitylimino)acenaphthene]dibromonickel activated by methylaluminoxane (MAO). The polar cyclic monomers need to be pretreated with an equimolar quantity of AlR3 as modifier. Triisobutylaluminium (TIBA) was found to be the preferred modifier for CL, whereas trimethylaluminium (TMA) was the preferred modifier for THF. Copolymerization of CL and E occurs at high activity of 1 to 10×106 g/(mol Ni×[E]×h); it is very much slower for THF and E. Characterizations by FTIR, DSC, mechanical properties and elemental analysis for C, H and N showed that novel high molecular weight (1.5 to 2.0×105) copolymers of E and CL were prepared containing about 14 CL units per chain. Terpolymerization of E, P and CL were also achieved for the first time. In contrast, the copolymerization involving THF was slower, favored by TMA pretreatment over TIBA and elevated temperature. A mechanism for E and CL copolymerization is proposed.