Influence of Crystallinity on the Mechanochemical Degradation of Poly(lactide) with Ball-Mill Grinding

Polymers can undergo mechanochemical chain scission during ball-mill grinding (BMG). Various milling and polymer parameters were known to influence chain scission, but the influence of crystallinity was not fully explored. In this report, using ring-opening polymerization, we prepared a library of poly(lactide)s (PLAs) with varying molecular weight and varying crystallinity by changing the stereochemistry of monomers. Semicrystalline PLLA and PDLA (from l- and d-lactide, respectively), amorphous PLDLA (from a copolymerization of l- and d-lactide), and a stereocomplex between PLLA and PDLA were subjected to degradation experiments to assess their degradation kinetics. We found degradation rate constant trends that suggested that the crystallinity had a negligible influence on degradation rates. We attributed this behavior to the fast amorphization of the semicrystalline PLAs. This work provides important insight into how other polymer transformations that occur during ball milling can influence chain scission.