Mechanically triggered on-demand degradation of polymers synthesized by radical polymerizations

Abstract

Polymers that degrade on demand have the potential to facilitate chemical recycling, reduce environmental pollution and are useful in implant immolation, drug delivery or as adhesives that debond on demand. However, polymers made by radical polymerization, which feature all carbon-bond backbones and constitute the most important class of polymers, have proven difficult to render degradable. Here we report cyclobutene-based monomers that can be co-polymerized with conventional monomers and impart the resulting polymers with mechanically triggered degradability. The cyclobutene residues act as mechanophores and can undergo a mechanically triggered ring-opening reaction, which causes a rearrangement that renders the polymer chains cleavable by hydrolysis under basic conditions. These cyclobutene-based monomers are broadly applicable in free radical and controlled radical polymerizations, introduce functional groups into the backbone of polymers and allow the mechanically gated degradation of high-molecular-weight materials or cross-linked polymer networks into low-molecular-weight species. Radical polymerizations yield polymers that cannot easily be degraded. The co-polymerization of cyclobutene-based monomers with conventional vinyl monomers has now been shown to result in co-polymers with cyclobutane mechanophores in their backbone, which facilitate on-demand degradation through a combination of mechanical activation and hydrolysis. This approach offers a promising avenue for the degradation of all-carbon-bond-backbone polymers.