Chemical recycling of polymers to monomer (CRM) is one of the most attractive methods to retain value in polymer materials during the recycling process. Polymers with low to moderate ceiling temperatures (<i>T</i><sub>c</sub>) are often employed in applications where recycling by depolymerization is desired. Polyacetals are a promising class of chemically recyclable polymers that exhibit a wide range of ceiling temperatures and mechanical properties that depend upon monomer structure. However, current catalyst systems for polyacetal synthesis are uncontrolled and produce polymers with low molecular weights, reducing the mechanical integrity of these materials and limiting their practical use. Furthermore, polyacetals produced by these systems often possess low thermal stabilities due to the presence of residual catalyst. To access well-defined high molecular weight polyacetals, we have developed a highly selective catalyst system that facilitates the controlled cationic ring-opening polymerization (CROP) of cyclic acetal monomers. High molecular weight polyacetals were synthesized at room temperature and possessed high thermal stability (Td &gt; 300 °C) in the absence of catalyst. Additionally, select polyacetals exhibit mechanical properties that rival those of polyolefins and can be selectively depolymerized from complex mixtures of plastic waste back to pure monomer at moderate temperatures using a separate depolymerization catalyst. The use of distinct polymerization and depolymerization catalysts allows for both synthesis and depolymerization of polyacetals under mild conditions, affording a practical method towards the catalytic conversion of polyacetals back to value-retained monomers.

Chemical recycling of mechanically robust polyacetals synthesized by living cationic ring-opening polymerization

ACS Spring 2022

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