Competing Time Scales in Surface-Driven Solution Depolymerization

Polymers that can undergo controlled or triggered depolymerization have garnered significant interest due to their use as recyclable or degradative materials. A variety of "self-immolative"chemistries have been developed, where this depolymerization process proceeds either spontaneously or upon application of a stimulus. Surface-driven polymer scission represents one possible process, where interaction with the surface can lead to the breaking of a chain into two portions. Despite the prevalence of this mode of depolymerization, there are few physical models to describe this process. In this paper, we develop a theoretical description of surface-driven scission, along with a competing "unzipping"process common in self-immolative polymers. This theory shows the role of competing diffusive and reactive time scales in determining depolymerization kinetics and how these time scales couple to the conformational statistics of a near-surface polymer chain. We also model the relationship between surface-driven and unzipping reaction kinetics, showing how they lead to different characteristics in the distribution of depolymerizing species. Coarse-grained simulations are also used to model these processes, and we can show agreement with our theory over a wide range of reaction kinetics, chain lengths, and depolymerization mechanisms. These models provide general predictions that can be used to inform the design and choice of self-immolative chemistries by connecting rate constants for individual reactions to the overall kinetics of depolymerization.