Catalyst‐Free Depolymerization of Aromatic and Aliphatic Polyesters Using Me3SiI

Abstract

Iodotrimethylsilane (Me₃SiI) promotes the depolymerization of a variety of alkyl and aromatic polyesters, such as poly(ethylene succinate) (PES), polylactic acid (PLA) as well as polyethylene and polybutylene terephthalates (PET, PBT), in the absence of catalyst. The monomer products, e. g. the silylester monomers and/or their value‐added derivatives, involving reactive iodo groups (alkyl iodides and acyl iodides), are obtained in high yields. The reaction outcomes are influenced by the solvent (e. g. CH₂Cl₂, CH₃CN), temperature (25 °C to 200 °C) and the amount of Me₃SiI. The depolymerization of PES gives the corresponding silylester which then cyclizes into succinic anhydride. With PLA, the ester CH₃CH₂CO₂SiMe₃ and propionyl iodide (CH₃CH₂COI) are formed. They can be selectively obtained by adjusting the reaction conditions. As expected, the decomposition of aromatic polymers PET and PBT affords the bis(trimethylsilyl) terephthalate compound (1,4‐{CO₂SiMe₃}₂C₆H₄). In the case of PET, the formation of the latter species is hampered by the I₂, released by the decomposition of the generated diiodoethane. The initial addition of an iodine trap (1‐pentyne) avoids these side reactions. This work demonstrates that the length of the carbon chain linking the carboxylic acid units is a crucial factor influencing the ease of the reaction and the nature of the products.