Catalyst-Free Depolymerization of Aromatic and Aliphatic Polyesters Using Me3SiI

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 choice (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.