High-Density Polyethylene with In-Chain Photolyzable and Hydrolyzable Groups Enabling Recycling and Degradation.

Polyethylenes endowed with low densities of in-chain hydrolyzable and photocleavable groups can improve their circularity and potentially reduce their environmental persistency. We show with model polymers derived from acyclic diene metathesis polymerization that the simultaneous presence of both groups has no adverse effect on the polyethylene crystal structure and thermal properties. Post-polymerization Baeyer-Villiger oxidation of keto-polyethylenes from non-alternating catalytic ethylene-CO chain growth copolymerization yield high molecular weight in-chain keto-ester polyethylenes (Mn ≈50.000 g mol-1 ). Oxidation can proceed without chain scission and consequently the desirable materials properties of HDPE are retained. At the same time we demonstrate the suitability of the in-chain ester groups for chemical recycling by methanolysis, and show that photolytic degradation by extended exposure to simulated sunlight occurs via the keto groups.

Molecularly Defined Polyolefin Vitrimers from Catalytic Insertion Polymerization.

Vitrimers can combine the advantageous properties of cross-linked materials with thermoplastic processability. For the prominent case of polyethylene, established post-polymerization introduction of cross-linkable moieties results in extremely heterogeneous compositions of the chains. Here, we report the generation of functionalized polyethylenes directly by catalytic insertion polymerization, with incorporated cross-linkable aryl boronic esters or alternatively acetal-protected groups suited for cross-linking with difunctional boronic esters. In addition to the desired homogeneous in-chain distribution, the reactive cross-linkable groups are enriched at the chain ends. This enables the incorporation of all chains in the network, as also supported by simulations of all chains' compositions. The uniform molecular composition of the chains reflects in resulting vitrimers' material properties, particularly lack of leaching with solvents. At the same time, cross-linking is indeed fully reversible and the vitrimers can be recycled.