Modeling ultrasound-induced molecular weight decrease of polymers with multiple scissile azo-mechanophores

The azo moiety is receiving increasing attention as a stimuli-responsive trigger. Herein, we present an investigation of the mechanoresponsive behavior of a series of polyurethanes containing multiple randomly distributed azo motifs as scissile mechanophores, i.e., an entity that is preferentially cleaved upon application of a mechanical force. We made a systematic comparison of the ultrasound-induced cleavage of azo-containing polymers of different molecular weights and with varying azo content. We developed a mathematical model to describe the scission kinetics and the analysis of the rate constants showed that site-specific cleavage at the azo position was favored over random bond scission events. The proposed mathematical model appears to be a broadly useful method to characterize the ultrasound-induced molecular weight decrease of polymers containing multiple scissile mechanophores.