- Advisor: Gregory I. Peterson ( https://gregpetersongip.wixsite.com/peterson-lab )

- Co-researchers: Kyoung Taek Kim (Seoul National University) , Tae-Lim Choi (ETH Zurich)

- Journal of the American Chemical Society  2023 , 145 , 18432−18438 ( https://doi.org/10.1021/jacs.3c04733 )

A series of monodisperse cyclic and linear poly(D,Llactide) s (c-PLA and l-PLA, respectively) were prepared with  various degrees of polymerization (DP) using an iterative  convergent synthesis approach. The absence of a molecular weight  distribution provided us a chance to study their mechanochemical  reactivity without obstructions arising from the size distribution. Additionally, we prepared l- and c-PLAs with identical DPs, which  enabled us to attribute differences in scission rates to the cyclic  polymer architecture alone. The polymers were subjected to  ultrasonication (US) and ball-mill grinding (BMG), and their  degradation kinetics were explored. Up to 9.0 times larger scission rates were observed for l-PLA (compared to c-PLA) with US, but  the difference was less than 1.9 times with BMG. Fragmentation requires two backbone scission events for c-PLA, and we were able  to observe linear intermediates (formed after a single scission) for the first time. We also developed a new method of studying the  dynamic memory effect in US by characterizing and comparing the daughter fragment molecular weight distributions of l- and c- PLAs. These results provide new insights into the influence of the cyclic polymer architecture on mechanochemical reactions as well as  differences in reactivity observed with US and BMG.