Palladium-catalyzed one-step synthesis of propylene-based hyperbranched polyolefin and its polar-functionalized derivatives

Abstract

The synthesis and application of palladium-catalyzed hyperbranched polyethylene and its polar functionalized derivatives have been extensively studied. In this research, two distinct types of backbone α-diimine palladium catalysts were employed to catalyze the polymerization of propylene and the copolymerization of propylene with methyl acrylate (MA) to prepare propylene-based hyperbranched polyolefin and polar functionalized polypropylene materials. During propylene polymerization, these palladium catalysts were capable of producing highly branched (160–225/1000C) polypropylene materials with moderate molecular weights (20.6–99.8 kg mol⁻¹). Notably, the rigid dibenzobarrelene-backbone palladium catalysts exhibited significantly higher polymerization activity compared to its corresponding flexible cyclohexyl-backbone palladium catalysts. Additionally, the smaller and more rigid cyclopentyl palladium catalysts demonstrated higher polymerization activity and produced polypropylene with a higher molecular weight compared to the larger and more flexible cyclohexyl catalysts. In the copolymerization of propylene with MA, these palladium catalysts effectively catalyzed the production of highly branched, moderate MA-content polar functionalized polypropylene materials. As the MA concentration increased, the copolymerization activity decreased, the molecular weight of the copolymers decreased, and the MA incorporation ratio significantly increased. Similar to propylene homopolymerization, the rigid dibenzobarrelene-backbone palladium catalysts exhibited significantly higher copolymerization activity in the copolymerization process. Furthermore, the cyclopentyl palladium catalysts catalyzed MA insertion more efficiently, resulting in copolymers with a higher incorporation ratio. Further NMR carbon spectrum analysis revealed that both the prepared polypropylene and polar functionalized polypropylene possessed hyperbranched microstructures.