Multiscale Control of Ultrahigh-Molecular-Weight Isotactic Poly(4-methyl-pentene-1) with Nascent Single-Crystal-like Morphology: From Molecular Synthesis to Macroscopic Properties

Isotactic poly(4-methyl-1-pentene) (iP4MP1) is a unique material known for its high transparency and gas permeability. iP4MP1 possesses high thermal and chemical stabilities, making it suitable for a wide variety of applications. We investigate the influence of polymerization medium on the resulting polymorphs and mechanical properties. By employing an aryl pyridylamido hafnium catalyst in a mixture of n-heptane and toluene, ultrahigh-molecular-weight UHMW-iP4MP1 having a unimodal distribution is achieved. The use of n-heptane as the polymerization solvent, where iP4MP1 chains are poorly miscible, resulted in the formation of metastable monoclinic Form II crystals, which below melting transform into the stable tetragonal Form I. The study demonstrates that crystallization kinetics during polymerization can be tailored to synthesize single-crystal-like iP4MP1. The low-entangled single-crystal-like iP4MP1 enables uniaxial deformation below the melting temperature, facilitating chain alignment. Consistent with the stereospecific nature of iP4MP, rheological analysis suggests high molecular weight between entanglements (M_e ≈ 26,000 g/mol). Mechanical properties of the synthesized polymers, including tensile strength, elongation at break, and toughness, increase with the molecular weight, highlighting the potential for achieving uniform mechanical properties required for advanced applications.