Linear, Graft, and Beyond: Multiblock Copolymers as Next-Generation Compatibilizers

Abstract

Properly addressing the global issue of unsustainable plastic waste generation and accumulation will require a confluence of technological breakthroughs on various fronts. Mechanical recycling of plastic waste into polymer blends is one method expected to contribute to a solution. Due to phase separation of individual components, mechanical recycling of mixed polymer waste streams generally results in an unsuitable material with substantially reduced performance. However, when an appropriately designed compatibilizer is used, the recycled blend can have competitive properties to virgin materials. In its current state, polymer blend compatibilization is usually not cost-effective compared to traditional waste management, but further technical development and optimization will be essential for driving future cost competitiveness. Historically, effective compatibilizers have been diblock copolymers or in situ generated graft copolymers, but recent progress shows there is great potential for multiblock copolymer compatibilizers. In this perspective, we lay out recent advances in synthesis and understanding for two types of multiblock copolymers currently being developed as blend compatibilizers: linear and graft. Importantly, studies of appropriately designed copolymers have shown them to efficiently compatibilize model binary blends at concentrations as low as ∼0.2 wt %. These investigations pave the way for studies on more complex (ternary or higher) mixed waste streams that will require novel compatibilizer architectures. Given the progress outlined here, we believe that multiblock copolymers offer a practical and promising solution to help close the loop on plastic waste. While a complete discussion of the implementation of this technology would entail infrastructural, policy, and social developments, they are outside the scope of this perspective which instead focuses on material design considerations and the technical advancements of block copolymer compatibilizers.

Ionic Compatibilization of Polymers

“…Nonetheless, the rheological and mechanical properties of 2:2 SBCPs can be markedly different than 1:1 and 1: n ionic copolymers. Conventional (covalently bonded) linear A–B multiblock copolymers can demonstrate greater toughness than corresponding diblock and triblock copolymers , and have significant potential as compatibilizers but can be challenging to synthesize with control over both the chain length and concentration of cycles. In comparison, ionic multiblock SBCPs can be prepared relatively easily and demonstrate better mechanical properties than diblock or triblock SBCPs.…”

Tailor-Made Functional Polyolefins of Complex Architectures: Recent Advances, Applications, and Prospects

“…Thus, developing efficient compatibilizers to valorize the massive quantities of plastic waste is indispensable. Traditional compatibilizers were based on diblock or graft copolymers generated in situ; however, the great potential of multiblock 201 and random 202 copolymers is currently being ascertained.…”

Copolymers Prepared by Exchange Reactions Enhance the Properties of Miscible Polymer Blends

“…For mixtures of incompatible polymers, small amounts of added multiblock copolymers can serve as compatibilizers. Effective multiblock copolymer compatibilizers can dramatically enhance the otherwise poor properties of these homopolymer mixtures and therefore are of interest for enabling or enhancing the recycling of mixed commodity plastics. , In a notable example by Bates, Coates, LaPointe, and coworkers, mixtures of polyethylene (PE) and isotactic polypropylene (iPP) showed higher toughness and strains at break when compatibilized with as little as 5 wt % of a multiblock PE–iPP copolymer. − In contrast to their ability to compatibilize immiscible polymers, the effects of adding multiblock copolymers to miscible polymer blends have not been explored. We hypothesized that multiblock polymers might improve the properties of miscible blends by increasing cohesive interactions or improving the organization of the polymer chains.…”