Polymer ultrasonication is a technique utilized to study how polymers break under mechanical force in solution and is an important predictive tool for the design of new mechanically-active materials. While there has been consensus stating that large polymers will undergo mechanically-driven scission events faster, the connotative definition of “large” has shifted from polymer molecular weight, to degree of polymerization (DP), to persistence length. Herein, we explored the effect of polymer tacticity on scission rate by sonicating isotactic (i) and syndiotactic (s) poly(methyl methacrylate) (PMMA) with similar DPs, allowing comparison of the effect of chain flexibility and radius of gyration (Rg) on mechanical activation without chemical alteration. Sonications were performed in triplicate with 70 kDa i- and sPMMA for 48 hours in THF at -5 °C at 2 mg/mL to measure the scission kinetics and minimize secondary scission events. Despite the differences in glass transition temperatures between sPMMA and iPMMA (130 and 50 °C, respectively) that would normally infer a large difference in chain flexibility, we found that sPMMA and iPMMA have nearly identical scission rates and Rg. Overall, this supports the idea that scission rate is independent of a polymers chain flexibility in solution ultrasonication. Broadly speaking, understanding the scission of polymers under flow has some critical implications industrially for their synthesis and processing but also bears some key fundamental promise in fields such as drag reduction or rheology modifiers.

PMMA tacticity has no effect on ultrasonication scission kinetics

ACS Spring Meeting 2021

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