Polyolefins remain one of the most impactful class of polymers with widespread use in single-use packaging applications. The popularity of polyolefins has resulted in their overwhelming presence in waste streams, where they are often disposed of in landfills and contribute to environmental pollution. Recycling of polyolefins is a promising avenue for minimizing polyolefin waste; however, this route suffers due to the diversity of structures that constitute different grades of polyolefins such as polyethylene. Linear low-density polyethylene (LLDPE) is a material that balances crystallinity and processability due to the presence of short chain branches (SCBs) governed by the introduction of α-olefin comonomers (<i>e.g.</i>, 1-butene) into the ethylene polymerization. While these SCBs serve as a convenient platform for tuning LLDPE properties, they also result in a complex library of polyethylene materials expressing a wide array of branch lengths, branch contents, and branch distribution along the polymer backbone; this diversity in LLDPE structure can make branching behavior difficult to quantify, especially when dealing with blocky or gradient copolymer structures, which further limits identification and separation of branched polyethylene from post-consumer waste streams. Here, we describe a series of model polyolefins derived from the ring opening metathesis polymerization (ROMP) of cyclic olefin monomers to allow for control of branch length, branch spacing, and polymer architecture in LLDPE analogs. We examine how polymerization conditions can be used to control structural properties of the polymers—including through the addition of excess ligands to modify polymerization kinetics—as well as how the choice of monomer influences polymer structure and, ultimately, defines the behavior of these model polyolefin derivatives. Characterization of the bulk and solution properties of these model platforms is used to outline strategies to assist in the identification and separation of this important class of thermoplastics, and how these strategically designed polymeric materials could be used to inform the construction of next-generation polymer blend compatibilizers.

Influence of branching behavior on the structure-property relationships of model linear low-density polyethylene derived from ring-opening metathesis polymerization

ACS Spring 2022

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