Biomimetic Chemocatalytic Cascades-A New Strategy for Molecular Design of Degradable Polymer Systems

Biological systems often involve cascading molecular signals; for example, blood coagulation involves a cascade of serial and parallel reactions catalyzed by enzymes. The present study draws inspiration from such complex biological systems to demonstrate, through a simple example, the purposeful design of a cascade system that enables control over polymer degradation kinetics. Micron size fibers of polylactide (PLA), cellulose acetate (CA), and their mixtures are subjected to hydrolysis at varying temperatures. Cleavage of the PLA produces an organic acid functional group that catalyzes the CA hydrolysis, thus demonstrating the use of synthetic molecular signaling. Furthermore, the presence of CA inhibits the degradation of PLA thereby demonstrating molecular feedback, another hallmark of biological molecular cascades. The parallel reaction cascade causes the hydrolysis rate constant for CA to increase 3.1 times compared to CA alone (from 5.7 × 10^-4 to 1.78 × 10^-3 L² mol^-2 h^-1 at 125 °C); furthermore, due to molecular feedback, the hydrolysis rate constant for PLA decreases by 21% (from 2.40 × 10^-3 to 1.90 × 10^-3 L² mol^-2 h^-1). The results demonstrate that synthetic signaling enables exquisitely tunable degradation kinetics. Technological applications of such purposely designed biomimetic systems are wide ranging and include the design of polymer systems for hydraulic fracturing, for biomedical applications, and for facilitating the recycling of mixed plastic wastes.