A Closer Look at the Substituent Effects on the Copolymerization of Thionolactones by Radical Ring-Opening Polymerization

The negative impact of plastic waste on the environment is a serious issue for the future. Adding cleavable bonds in the polymer backbone can help to impart degradability properties. To this end, radical ring opening polymerization (rROP) of-fers a very attractive way through radical copolymerization with vinyl monomers. Thionolactones, one of the various cyclic monomers that can be used in rROP, are promising structures due to the efficiency of the C=S bond in acting as a radical acceptor. In this work, we used DFT calculations to better understand the effects of different substituents on the radical reac-tivity of thionolactones (dibenzo[c,e]oxepane-5-thione DOT derivatives) already described as more or less effective for copol-ymerization with vinyl monomers in order to adjust the reactivity of these thionolactones. To carry out these calculations, we focused on the value of the transfer constant ktr and its relationship to the propagation constant kp of the vinyl monomer. The calculations performed subsequently on 7-phenyloxepane-2-thione (POT) derivatives highlighted that electron-donating groups inserted in para-position on the phenyl ring should improve the copolymerization efficiency with acrylate derivatives and in contrary electron-withdrawing groups should lead to more important compositional drift during styrene and acrylate copolymerization. Although POT derivatives bearing electro-donating groups could not be prepared, the preparation of those with CF3 and NO2 groups was successfully achieved. Experimental copolymerization of these two thionolactones with sty-rene and isobornyl acrylate are in good agreement with the calculations. This result confirmed the versatility and relevance of our calculation approach to account for the reactivity of thionolactones.