Degradable Polystyrene via the Cleavable Comonomer Approach

Polystyrene (PS) is a major commodity polymer, widely used in various applications ranging from packaging to insulation thanks to its low cost, high stiffness and transparency as well as its relatively high softening temper-ature. Similarly to all polymers prepared by radical polymerization, PS is constituted of a C-C backbone and thus is not degradable. To confer degradability to such materials, the copolymerization of vinyl monomers with cyclic monomer that could undergo radical ring-opening is an efficient methodology to introduce pur-posely cleavable bonds into the polymer backbone. Dibenzo[c,e]-oxepane-5-thione (DOT) is a cyclic thionolac-tone monomer known for its efficient copolymerization with acrylate derivatives but so far could not be incor-porated into PS backbones. From a theoretical study combining DFT and kinetic models using the PREDICI software, we showed that modifying experimental conditions could overcome these limitations and that high molar mass degradable polystyrene (Mw close to 150,000 g.mol-1) could be prepared via statistical insertion of thioester groups into the polymer backbone. Thanks to favorable reactivity ratios allowing only a few mol% of thioester units to be randomly incorporated, there was no major modification of the thermal and mechanical properties of the PS. The degradation of such PS could be performed in THF at RT in one hour using 1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD) as a base, leading to oligomers with Mn close to 1,000 g.mol-1. We success-fully demonstrate further applicability of these copolymerization systems for the photo-triggered decomposi-tion of PS in solution as well as the synthesis of cross-linked PS networks degradable into soluble side-products