Approaches to Sustainable and Continually Recyclable Cross-Linked Polymers

Abstract

Cross-linked polymers are ubiquitous in daily life, finding applications as tires, insulation, adhesives, automotive parts, and countless other products. The covalent crosslinks in these materials render them mechanically robust, chemically resistant, and thermally stable, but they also prevent recycling of these materials into similar-value goods. Furthermore, cross-linked polymers are typically produced from petroleumbased feedstocks, and their hydrocarbon backbones render them nondegradable, making them unsustainable in the long term. In recent years, much effort has focused on the development of recycling strategies for cross-linked polymeric materials. In the following Perspective, we discuss many of these approaches, and highlight efforts to sustainably produce recyclable crosslinked polymers. We present our thoughts on future challenges that must be overcome to enable widespread, viable, and more sustainable and practical implementation of these materials, including the sustainable sourcing of feedstocks, long-term environmental stability of inherently dynamic polymers, and moving toward industrially viable synthesis and reprocessing methods.

Conformational Entropy as a Means to Control the Behavior of Poly(diketoenamine) Vitrimers In and Out of Equilibrium

“…Vitrimers are living polymer networks that reconfigure via dynamic associative bond-exchange reactions,l aying the foundations for both self-healing plastics and post-industrial plastics recycling. [1][2][3] Thec ross-linking density of av itrimer influences its thermal and mechanical properties:f or example,h igher network density increases the probability that cross-links will interact and be involved in bond-exchange reactions,w hich impact the dynamics of vitrimer reconfigurability across multiple length scales and therefore its rheology. Theenergetics of bond-exchange reactions have been studied for vitrimers undergoing uncatalyzed or catalyzed transesterification, [4][5][6] transcarbamoylation, [7][8][9][10] olefin metathesis, [11] boronic ester exchange, [12][13][14] siloxane exchange, [15,16] triazo-lium transalkylation, [17] imine bond exchange, [18,19] ketoenamine exchange, [20][21][22] and diketoenamine exchange.…”

Selective Degradation of End‐of‐Life Poly(lactide) via Alkali‐Metal‐Halide Catalysis

“…[1,2] However, several issues arise with plastics after the service life ends. [4][5][6][7][8][9] Finally, these treatments convert chemical functions of the polymers into harmful chemicals, for instance, carbon dioxide, consequently affecting on the anthroposphere (e.g., global warming). [4][5][6][7][8][9] Finally, these treatments convert chemical functions of the polymers into harmful chemicals, for instance, carbon dioxide, consequently affecting on the anthroposphere (e.g., global warming).…”

“…[3] In more detail, the current management for end-of-life (EoL) plastic streams is mainly based on energy recovery, (landfill storage), recycling (mechanical and downcycling), and unregulated release to the environment. [4][5][6][7][8][9] Finally, these treatments convert chemical functions of the polymers into harmful chemicals, for instance, carbon dioxide, consequently affecting on the anthroposphere (e.g., global warming). Importantly, for fresh polymers the declining fossil resources are required.…”

Conformational Entropy as a Means to Control the Behavior of Poly(diketoenamine) Vitrimers In and Out of Equilibrium

“…Vitrimers are living polymer networks that reconfigure via dynamic associative bond‐exchange reactions, laying the foundations for both self‐healing plastics and post‐industrial plastics recycling . The cross‐linking density of a vitrimer influences its thermal and mechanical properties: for example, higher network density increases the probability that cross‐links will interact and be involved in bond‐exchange reactions, which impact the dynamics of vitrimer reconfigurability across multiple length scales and therefore its rheology.…”