Crystalline Isotactic Polar Polypropylene from the Palladium‐Catalyzed Copolymerization of Propylene and Polar Monomers

Abstract

AbstractModerately isospecific homopolymerization of propylene and the copolymerization of propylene and polar monomers have been achieved with palladium complexes bearing a phosphine‐sulfonate ligand. Optimization of substituents on the phosphorus atom of the ligand revealed that the presence of bulky alkyl groups (e.g. menthyl) is crucial for the generation of high‐molecular‐weight polypropylenes (Mw≈104), and the substituent at the ortho‐position relative to the sulfonate group influences the molecular weight and isotactic regularity of the obtained polypropylenes. Statistical analysis suggested that the introduction of substituents at the ortho‐position relative to the sulfonate group favors enantiomorphic site control over chain end control in the chain propagation step. The triad isotacticity could be increased to mm=0.55–0.59, with formation of crystalline polar polypropylenes, as supported by the presence of melting points and sharp peaks in the corresponding X‐ray diffraction patterns.