Ring‐Opening Polymerization of Cyclic Acetals: Strategy for both Recyclable and Degradable Materials

Abstract

To cope with the severe plastic waste crisis, massive efforts are made to develop sustainable polymer materials whose degradation involves a disposing and decomposing to small molecule (DDM) and/or a chemical recycling to monomer (CRM) process. Polyacetals, a type of pH-responsive polymers, are degradable under acidic conditions, while highly stable under neutral and basic circumstances. As for their synthesis, the cationic ring-opening polymerization (CROP) of cyclic acetals is an elegant and promising approach, though suffering from fatal side reactions and polymerization-depolymerization equilibrium. Recent development in CRM restimulates the interest in the long-forgotten CROP method due to its inherent depolymerization characteristics. In terms of the end-of-life options, polyacetals are recyclable materials with both DDM and CRM potentials. They not only expand the scope of materials for closed-loop recycling but also help to tune the degradation properties of traditional polyesters and polyolefins. This review aims to discuss the synthesis of various polyacetals by CROP and their degradation properties from the perspectives of 1) polymerization of cyclic acetals, dioxepins, and hemiacetal esters, 2) copolymerization of cyclic acetals with heterocyclic or vinyl monomers, and 3) degradation and recycling properties of the related polymers.

Synthesis and polymerization of cyclic formals of oligooxyethylene diols

“…Polymers of TCO‐1,3,6‐trioxacyclooctane (2EO‐MO), TCU‐1, 3,6,9‐tetraoxacycloundecane (3EO‐MO) and PCT‐1, 3,6,9,12‐pentaoxacyclotetradecane (4EO‐MO) are composed of alternating formaldehyde units and ethylene glycol units with diverse compositions (xEO‐MO) affording the corresponding polymers with successive changes in properties such as hydrophilicity and ion diffusivity 29 . Thus, polymers of higher cyclic formals (−[EO] m ‐MO) n may be treated as intermediate between PDXL and POE.…”

Microreactor-Based Green Synthetic Platform for Flow Synthesis of Biodegradable Polymers

“…Biodegradable polymers have attracted growing interest from both academia and the public in the background of global attention to sustainable development. − According to the functional groups in the polymer main chain, biodegradable polymers include but are not limited to aliphatic polyester, poly­(ester amide), polycarbonate, polyphosphoester, polyacetal, and polyurethane. These biodegradable polymers are widely used in tissue engineering, drug delivery, eco-friendly package, electronics, etc. − Among them, the syntheses and applications of aliphatic polyester and polycarbonates as the typical classes of biodegradable polymers have been investigated in the last decades. − Catalytic ring-opening polymerizations (ROPs) of cyclic monomers, such as ε-caprolactone (CL), δ-valerolactone (VL), lactide (LA), and trimethyl carbonate (TMC), in batch reactors represent the main synthetic approach to preparing well-defined aliphatic polyesters and polycarbonates. , The development of green synthetic platforms is highly desired for the fabrication of high-performance biodegradable polymers.…”

Easy Access to Ultrahigh-Molecular Weight Poly(1,3-dioxolane) by Rare Earth Triflates

“…Cyclic acetals are polymerized exclusively via cationic ring-opening polymerization (CROP). , It is a reversible reaction with a polymerization–depolymerization equilibrium, which further limits the MW of the polyacetals. Polyoxymethylene (POM), the only polyacetal made on an industrial scale, is synthesized via heterogeneous CROP of triformaldehyde (TOX) with high MW and is widely used in precision parts due to its high stiffness and low friction .…”