Synthesis of Micro 14C-Labeled Polylactide forEnvironmental Assessment Analysis

Polylactide (PLA), a biobased, biodegradable polyester derived from lactic acid, is recognized as an alternative to conventional plastics due to properties such as mechanical strength and compostability. Despite widespread use in applications from medical devices to packaging, PLA degradation in the environment, particularly its breakdown into microplastics, raises concerns. Conventional analytical methods are inadequate for quantifying PLA degradation in environments. To address this, radio tracking techniques using carbon-14 have emerged as a reliable method for PLA decomposition studies. The first step is producing labeled polymers from suitable monomers. Ring-opening polymerization (ROP) of lactide is widely used for synthesizing PLA, but this approach faces challenges due to the limited availability and high cost of 14C-labeled precursors. We report the first use of a biocompatible zinc bisguanidine catalyst for the synthesis of 14C-lactide from 14C-lactic acid, enabling the production of 14C-PLA. The process involves dehydration and oligomer formation, followed by catalytic depolymerization to yield 14C-lactide, which is polymerized through ROP. Lactide production was optimized by comparing the toxic industrial catalyst tin(II) octanoate [Sn(Oct)2] with our catalyst, the latter ultimately used for 14C-lactide and 14C-PLA production. The resulting micro-14C-labeled PLA can be used to quantify degradation, assess environmental impact.