Palladium-catalyzed synthesis of low viscosity hyperbranched liquid polyethylene and its polar copolymers

Abstract

In this investigation, we designed and synthesized a range of pyridine-imine Pd(II) complexes featuring 2-aryl and 6-diphenylmethyl substituents. These catalysts were specifically tailored for the preparation of hyperbranched polyethylene oils (HBPEOs) and polar-functionalized hyperbranched polyethylene oils (PFHBPEOs). The catalysts exhibited high activity in the synthesis of HBPEO, achieving rates as high as 2.97–17.67 × 104 g mol−1 h−1. The resulting products were characterized by low molecular weights ranging from 307 to 500 g/mol, high branching densities of 113–138/1000C, and correspondingly low viscosities. While demonstrating moderate activity in the range of 0.7–6.2 × 103 g mol−1 h−1 for the synthesis of PFHBPEO, the polar-functionalized hyperbranched polymers retained similar characteristics of low molecular weight (325–436 g/mol), high branching density (112–141/1000C), and low viscosity. Notably, the PFHBPEOs obtained through this process exhibited an exceptionally high insertion ratio (7.4–16.0 mol%) of MA, with the ester group positioned terminally on the long chain branching. NMR analysis further confirmed the presence of a diverse range of branching structures, with a significant proportion of hyperbranched motifs, in both HBPEO and PFHBPEO. Importantly, variations in the catalyst structure and polymerization conditions were found to significantly influence the activity, structural features, and properties of the resulting HBPEO and PFHBPEO.