Selective Chain Scission of L-Lactide/ε-Caprolactone Chain Shuttled Copolymers

In this work, we investigated selective strategies for the degradation of L-lactide/ε-caprolactone chain shuttled multiblock copolymers composed of PLLA-rich hard blocks and poly(ε-caprolactone-co-L-lactide) soft blocks. Enzymatic hydrolysis using the selective lipase from Pseudomonas cepacia, initially performed in aqueous buffer systems and subsequently in the presence of organic cosolvents, showed limited efficiency, likely due to limited enzymatic accessibility within the complex multiblock architecture. In contrast, homogeneous organocatalytic approaches showed higher degradation efficiency and selectivity. Base-catalyzed transesterification using 4-dimethylaminopyridine (DMAP) and imidazole enabled 100% selective chain scission toward lactyl units. Brønsted acid catalysis with p-toluenesulfonic acid (pTSA) and diphenyl phosphate (DPP) exhibited complementary transesterification selectivity, favoring degradation of caprolactoyl units and thus targeting the soft segments. The latter selectivity is particularly interesting, as it provides structural information about the chain-shuttled copolymers and allows to envision recycling of the PLA part. It is corroborated by DFT studies.