Accessibility of responsive end-caps in films composed of stimuli-responsive, depolymerizable poly(phthalaldehydes)

Polymers that are capable of depolymerizing completely from head-to-tail upon cleavage of an end-cap from the terminus of the polymer have emerged recently as a new strategy for creating stimuli-responsive solid-state materials with amplified responses. In theory, solid-state materials made from these polymers will respond most efficiently to a stimulus in solution when the polymer end-caps are displayed into solution at the solid-liquid interface, rather than being buried in the solid-state material. This article defines two strategies for increasing the likelihood that end-caps are displayed at this interface. A microscale-pump made from films of depolymerizable poly(phthalaldehyde) serves as a test system for evaluating the location of end-caps in the films. By measuring the flow rate initiated by depolymerization of the polymers within the films, we determined that both the polymer length and hydrophilicity of the end-caps affect the density of end-caps at the solid-liquid interface.