Highly cis-1,4 selective copolymerization of dienes with polar 2-(3-methylidenepent-4-en-1-yl)pyridine: an approach to recyclable elastomers
Incorporating polar functional group into macromolecular chains of rubber materials via coordination polymerization is a theoretical challenge. In this work, we report the coordination copolymerization of a new polar diene-based monomer, 2-(3-methylidenepent-4-en-1-yl)pyridine (MBEF), with isoprene or butadiene by using a ternary catalytic system composed of bis(phosphino)carbazolide yttrium bis(alkyl) complex, [Ph3C][B(C6F5)4] and AlEt3. The resultant copolymers have high cis-1,4 regularity (> 97%) as well as tuneable polar monomer incorporation ratios. In addition, the pendent polar pyridine groups can be clearly and quantitatively converted into pyridine quaternary ammonium chloride or iodide salt under mild conditions. Aggregation of the quaternary ammonium salt plays the role of physical cross-linking joint, which endows the copolymer with high mechanical property and improved polarity. Moreover, these ionic cross-linking polyisoprene based elastomers exhibit remarkable thermal reshaping and recycling properties.