Pd(II)-catalyzed ethylene/methyl acrylate copolymerization: toward catalyst recovery and recycle

Abstract

The paradigm shift from linear to circular economy is a very important goal, which concerns several fields of chemistry, including the recycle of plastic materials and of critical raw materials, including platinum group metal catalysts. The introduction of polar functional groups into the polyolefin skeleton, to yield functionalized polyolefins (FPO), might open new and easier pathways for plastic depolymerization processes compared to simple polyolefins. However, the homogeneously catalyzed, controlled copolymerization of ethylene with polar vinyl monomers, to produce FPO, is a highly challenging reaction; at present, Pd-α-diimine complexes are the most promising catalysts for this reaction. In this contribution, we have revisited the catalytic behavior of three known palladium complexes with benchmark α-diimines (N-N) of general formula [Pd(N-N)(Me)(NCMe)][PF6], by carrying out, for the first time, the copolymerization of ethylene with methyl acrylate in trifluoroethanol/dichloromethane mixtures of different composition. We found an unprecedented effect of the solvent composition on catalyst productivity, content of inserted polar monomer and its way of incorporation. Moreover, at specific solvent compositions the spontaneous formation of two phases occurred at the end of the catalytic runs. We exploited this phenomenon to successfully perform, for the first time in this field, the recovery and recycling of the catalyst.