We report the preparation, structural characterization, and detailed lactide polymerization behavior of a new Zn(II) alkoxide complex, (L(1)ZnOEt)(2) (L(1) = 2,4-di-tert-butyl-6-{[(2'-dimethylaminoethyl)methylamino]methyl}phenolate). While an X-ray crystal structure revealed the complex to be dimeric in the solid state, nuclear magnetic resonance and mass spectrometric analyses showed that the monomeric form L(1)ZnOEt predominates in solution. The polymerization of lactide using this complex proceeded with good molecular weight control and gave relatively narrow molecular weight distribution polylactide, even at catalyst loadings of <0.1% that yielded M(n) as high as 130 kg mol(-)(1). The effect of impurities on the molecular weight of the product polymers was accounted for using a simple model. Detailed kinetic studies of the polymerization reaction enabled integral and nonintegral orders in L(1)ZnOEt to be distinguished and the empirical rate law to be elucidated, -d[LA]/dt = k(p)[L(1)ZnOEt][LA]. These studies also showed that L(1)ZnOEt polymerizes lactide at a rate faster than any other Zn-containing system reported previously. This work provides important mechanistic information pertaining to the polymerization of lactide and other cyclic esters by discrete metal alkoxide complexes.

Highly active zinc catalyst for the controlled polymerization of lactide.

Whilst plastics have played an instrumental role in human development, growing environmental concerns have led to increasing public scrutiny and demands for outright bans. This has stimulated considerable research into renewable alternatives, and more recently, the development of alternative waste management strategies. Herein, the aim was to highlight recent developments in the catalytic chemical recycling of two commercial polyesters, namely poly(lactic acid) (PLA) and poly(ethylene terephthalate) (PET). The concept of chemical recycling is first introduced, and associated opportunities/challenges are discussed within the context of the governing depolymerisation thermodynamics. Chemical recycling methods for PLA and PET are then discussed, with a particular focus on upcycling and the use of metal-based catalysts. Finally, the attention shifts to the emergence of new materials with the potential to modernise the plastics economy. Emerging opportunities and challenges are discussed within the context of industrial feasibility.

https://chemistry-europe.onlinelibrary.wiley.com/doi/pdf/10.1002/cssc.202100400

The Chemical Recycling of Polyesters for a Circular Plastics Economy: Challenges and Emerging Opportunities.

Chemically recyclable polymer materials: polymerization and depolymerization cycles

Review of polymer technologies for improving the recycling and upcycling efficiency of plastic waste.

The development of innovative synthetic polymer systems to overcome the trade-offs between the polymer's depolymerizability and performance properties is highly demanded for advanced material applications and sustainable development. In this contribution, we prepared a class of aromatic cyclic esters ( M1 - M5 ) from thiosalicylic acid and epoxides by facile one-pot synthesis. Ring-opening polymerization of M s afforded aromatic polyesters P( M )s with high molecular weights and narrow dispersities. The physical and mechanical properties of P( M )s can be modulated by stereocomplexation and regulation of the side-chain flexibility of the polymers, ultimately achieving high-performance properties such as high thermal stability and crystallinity ( T m up to 209 °C), as well as polyolefin-like high mechanical strength, ductility, and toughness. Furthermore, the functionalizable moieties of P( M )s have driven a wide array of post-polymerization modifications toward access to value-added materials. More importantly, the P( M )s were able to selectively depolymerize into monomers in excellent yields, thus establishing its circular life cycle.

Advancing the Development of Recyclable Aromatic Polyesters by Functionalization and Stereocomplexation.

Plastics recycling has become an important issue based on the principle of sustainability and circular economy. Therefore, the development of a valuable chemical recycling method, to achieve the recycling process of end-of-life polylactide (PLA) waste without loss of material properties, meets unprecedented opportunities. In this regard, we propose a “DE–RE polymerization” strategy to achieve the recycling process from end-of-life PLA plastic waste to new virgin-quality PLA materials in a “polymer to polymer” mode. This approach improves the efficiency of PLA recycling and promotes the development of plastics reutilization. 

A “Polymer to Polymer” Chemical Recycling of PLA Plastics by the “DE–RE Polymerization” Strategy

Selective, Sequential, and “One-Pot” Depolymerization Strategies for Chemical Recycling of Commercial Plastics and Mixed Plastics

Zn(HMDS)2 as a simple, biocompatible, efficient, and supporting ligand-free metal catalyst has been achieved for polyesters synthesis and degradation. The catalyst not only has a powerful capacity ...

Zn(HMDS)2 as a Versatile Transesterification Catalyst for Polyesters Synthesis and Degradation toward a Circular Materials Economy Approach

Asymmetric kinetic resolution polymerization

Chemical recycling of plastic wastes not only provides a practical pathway to solve the end-of-use issue of polymer materials but also offers a possible closed-loop approach for mainly fossil-based materials, which has drawn tremendous attention from academia and industry. Poly(bisphenol A carbonate) (BPA-PC), a typical shock-resistant thermoplastic material, which has been used increasingly all over the world, should receive extensive attention for its potential environmental harm, as well as its chemical recycling route. For BPA-PC, traditional disposal methods, such as landfills, are unable to prevent the spread of BPA as a possible xenoestrogen and may cause secondary pollution to air and soil. Herein, an “amino-alcoholysis” strategy has been proposed, which upcycles BPA-PC plastic waste to BPA monomers and high value-added chiral 2-oxazolidinone chemicals via ZnX2-catalyzed depolymerization by chiral amino alcohols under mild conditions. Moreover, sequential depolymerization of BPA-PC/poly(ethylene terephthalate) (PET) mixed plastics was also achieved with high yields and selectivities. This strategy demonstrates a method for the diversified transformation of BPA-PC plastic waste to BPA and high value-added chiral chemicals. 

Chemical Upcycling of Poly(bisphenol A carbonate) Plastic Catalyzed by ZnX2 via an Amino-Alcoholysis Strategy

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