No abstract

Adhesives that selectively debond from a surface by stimuli-induced head-to-tail continuous depolymerization of poly(benzyl ether) macro-cross-linkers within a poly(norbornene) matrix are described. Continuous head-to-tail depolymerization provides faster rates of response than can be achieved using a small-molecule cross-linker, as well as responses to lower stimulus concentrations. Shear-stress values for glass held together by the adhesive reach 0.51±0.10 MPa, whereas signal-induced depolymerization via quinone methide intermediates reduces the shear stress values to 0.05±0.02 MPa. Changing the length of the macro-cross-linkers alters the time required for debonding, and thus enables the programmed sequential release of specific layers in a glass composite material.

Mechano-activated chemistry is a powerful tool for remodeling of synthetic polymeric materials, however, few reactions are currently available. Here we show that using piezochemical reduction of a Cu -based pre-catalyst, a step-growth polymerization occurs via the copper catalyzed azide-alkyne cycloaddition (CuAAC) reaction to form a linear polytriazole. Furthermore, we show that a linear polymer can be crosslinked mechanochemically using the same chemistry to form a solid organogel. We envision that this chemistry can be used to harness mechanical energy for constructive purposes in polymeric materials.

This Communication describes a strategy for incorporating detection units onto each repeating unit of self-immolative CDr polymers. This strategy enables macroscopic plastics to respond quickly to specific applied molecular signals that react with the plastic at the solid-liquid interface between the plastic and surrounding fluid. The response is a signal-induced depolymerization reaction that is continuous and complete from the site of the reacted detection unit to the end of the polymer. Thus, this strategy retains the ability of CDr polymers to provide amplified responses via depolymerization while simultaneously enhancing the rate of response of CDr-based macroscopic plastics to specific applied signals. Depolymerizable poly(benzyl ethers) were used to demonstrate the strategy and now are capable of depolymerizing in the context of rigid, solid-state polymeric materials.

This Communication describes a chemically responsive polymer film that is capable of detecting low levels of a specific applied molecular signal (thiol) and subsequently initiating a self-propagating reaction within the material that converts the nonfluorescent film into a globally fluorescent material. We illustrate that the intensity of the resulting fluorescent material is independent of the quantity of the applied thiol, whereas the rate to reach the maximum level of signal is directly proportional to the quantity of the signal. In contrast, a control film, which lacks functionality for mediating the self-propagating reaction, provides a maximum change in fluorescence that is directly proportional to the quantity of the applied thiol. This level of nonamplified signal is 78% lower in intensity (when initiated with 100 µM of applied thiol) than is achieved when the material contains functionality that supports the self-powered, self-propagating amplification reaction.