Nonlinear Ziegler–Natta-Homopolyethylene with Enhanced Crystallinity: Physical and Macromolecular Characteristics

Polyolefin engineering and design are at the forefront of a significant number of research and development laboratories, helping to bring about new and highly specific materials for tailored uses. Tailoring the chain architecture of polyolefins improves their performance and physical properties. Four unique polyethylene (PE) materials with long-chain branches (LCBPE) are studied using advanced chromatographic fractionation techniques alongside linear high-density PE (HDPE) and typical commercial low-density PE (LDPE). The absence of short-chain branching in the analyzed LCBPEs allows for a defined correlation of long-chain branching (LCB) with specific physical properties. Possible effects of side-chain crystallization on melt behavior and crystallinity clearly show that the nonlinearity in architecture positively affects crystallinity while simultaneously lowering melting temperature. The separation of polyolefins according to the LCB content is demonstrated for the first time by high-temperature interaction chromatography and thermal analysis, in addition to size exclusion chromatography coupled to differential viscometer and light scattering detectors. This study is pioneering in applying solvent gradient interaction chromatography and stationary-phase-assisted crystallization to the separation of PE regarding long-chain branching.