Polyethylene (PE) and isotactic polypropylene (PP) constitute nearly two-thirds of the world's plastic. Despite their similar hydrocarbon makeup, the polymers are immiscible with one another. Thus, common grades of PE and PP do not adhere or blend, creating challenges for recycling these materials. We synthesized PE/PP multiblock copolymers using an isoselective alkene polymerization initiator. These polymers can weld common grades of commercial PE and PP together, depending on the molecular weights and architecture of the block copolymers. Interfacial compatibilization of phase-separated PE andPP with tetrablock copolymers enables morphological control, transforming brittle materials into mechanically tough blends.

Polyethylene-graft-poly(methyl methacrylate) (PE-g-PMMA) copolymers were prepared using a combination of ring-opening metathesis polymerization (ROMP), hydrogenation, and atom transfer radical polymerization (ATRP). Approximately 20 PMMA side chains per molecule with average degrees of polymerization 6, 12, and 24 were grown via a “grafting from” approach from a Br-substituted linear PE backbone with M w = 56 000. The resulting graft copolymers were evaluated as compatibilizing agents for binary PE/PMMA homopolymer blends. The roles of PMMA side chain length and different compatibilizer concentration in the polymer blends were investigated, and the mechanical and morphological properties of blends containing 70% PE and 30% PMMA by weight were examined. The presence of the compatibilizer reduced the average PMMA droplet size substantially, even at compatibilizer loadings as low as 1%. Furthermore, the compatibilized blends exhibited significant improvements in elastic modulus, yield strength, and scratch resistance as compared to the binary blends. Adhesion testing confirmed the ability of PE-g-PMMA to act as an effective PE/PMMA adhesion promoter. Remarkably, the graft copolymer with the shortest side chains was the most effective compatibilizer. This counterintuitive result is tentatively attributed to kinetic limitations in partitioning of the graft copolymers to the interface.

Poly­(methyl methacrylate)-block-polyethylene-block-poly­(methyl methacrylate) (PMMA–PE–PMMA) triblock copolymers were prepared by a combination of ring-opening metathesis polymerization (ROMP), hydrogenation, and reversible addition–fragmentation chain-transfer (RAFT) polymerization. The number-average molar masses of the PMMA end blocks were varied (M n = 1, 4, 12, and 31 kg mol–1), whereas that of the PE middle block was kept constant at M n = 13 kg mol–1. The copolymers were evaluated as compatibilizers in PE/PMMA homopolymer blends containing PE in a 4:1 excess by weight. The compatibilized blends displayed significant improvements in elastic modulus, hardness, and scratch resistance as compared to uncompatibilized binary blends. The effects of the PMMA end-block molar mass and compatibilizer concentration on the blend morphology and mechanical properties were investigated. The triblock copolymer with the highest-molar-mass PMMA end blocks was most effective, presumably because of enhanced stress transfer between phases by virtue of a higher degree of entanglement of the end blocks with the PMMA dispersed phase.

We show catalyst localized at the interface can compatibilize polyethylene (PE) and polylactide (PLA) blends. Telechelic hydroxyl functional PE was synthesized by ring opening metathesis polymerization, which reacted with PLA in melt mixing (shown by adhesion and droplet size reduction). Lewis acid tin catalysts were examined as interfacial reaction promoters, with the goal of interfacial localization. Stannous octoate was shown to localize at the interface by transmission electron microscopy with energy dispersive X-ray spectroscopy and improved dispersion of PLA in PE as compared to uncatalyzed materials and a nonlocalized tin chloride dihydrate.

Polylactide (PLA) is a promising material, with favorable modulus, renewable sources, and biodegradability. However, its low extension at break (4–7%) and toughness (notched Izod, 26 J/m) limit its applications (Anderson et al., Polym. Rev., 48, 85 (2008)). PLA toughening has been the subject of recent reviews, and is the basis for several commercial products. This work aims to increase PLA toughness using rubbery, linear low‐density polyethylene (LLDPE), glycidyl methacrylate functional PE compatibilizer (EGMA), and novel catalysts that promote copolymer formation at the interface of immiscible blends of PLA and EGMA/LLDPE. Droplet size was reduced from 2.7 µm to 1.7 µm with addition of 5 wt% EGMA, and further to 1.0 µm with the addition of cobalt octoate catalyst. Extension at break of 200% is achieved with only 5 wt% EGMA, 15 wt% LLDPE, and 0.01 M cobalt octoate, leading to an increase in tensile toughness of over an order of magnitude (compared to neat PLA). This work demonstrates that catalysts can reduce the amount of reactive compatibilizer necessary to achieve a given PLA toughness. POLYM. ENG. SCI., 58:28–36, 2018. © 2017 Society of Plastics Engineers