Commercial polyolefins, which often involve mixtures and copolymers of linear, short-chain branched, and long-chain branched macromolecules, can be very challenging to characterize as species with similar hydrodynamic sizes or solubility often co-elute in various chromatographic methods. Quantifying the molar mass, chemical composition, and architectural distributions within these materials is crucial for determining accurate structure-property-performance relationships, especially for polyolefin-based thermoplastic elastomers, which include block copolymers (BCP) of crystalline and amorphous polyolefin segments. Model linear low-density polyethylene (LLDPE) – polyethylene block copolymers were synthesized by ring-opening metathesis polymerization (ROMP) of 1-alkyl-trans-cyclooctenes with successive hydrogenation. The alkyl branch frequency and branch length along the LLDPE block was fixed, while systematically varying the block lengths of the LLDPE and HDPE blocks. While ROMP of 3-cis-cyclooctene BCPs have been previously reported in the literature,1 the use of the higher ring strain trans monomer with alkyl substitution directly at the alkene permit high target molar masses (≥ 100 kg/mol) and limit secondary metathesis that would randomize the copolymer sequence during formation of the second block. These polyalkenamer polymers were first analyzed by triple detector exclusion chromatography (SEC) to characterize the molar mass distribution, Mark-Houwink parameters, and radius of gyration (Rg) of the first block and resultant BCP. Upon subsequent hydrogenation, the polylefin BCPs were analyzed with high-temperature SEC to determine the short chain branching content across the molar mass distribution and compare changes in intrinsic viscosity and Rg with variation of the block length.

Synthesis and characterization of model linear low-density polyethylene copolymers towards quantitative structure-property relationships

ACS Fall 2020 Virtual Meeting

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