Selective Electrochemical Modification and Degradation of Polymers.

We demonstrate that electrochemical-induced decarboxylation enables reliable post-polymerization modification and degradation of polymers. Polymers containing N-(acryloxy)phthalimides were subjected to electrochemical decarboxylation under mild conditions, which led to the formation of transient alkyl radicals. By installing these redox-active units, we systematically modified the pendent groups and chain ends of polyacrylates. This approach enabled the production of poly(ethylene-co-methyl acrylate) and poly(propylene-co-methyl acrylate) copolymers, which are difficult to synthesize by direct polymerization. Spectroscopic and chromatographic techniques reveal these transformations are near-quantitative on several polymer systems. Electrochemical decarboxylation also enables the degradation of all-methacrylate poly(N-(methacryloxy)phthalimide-co-methyl methacrylate) copolymers with a degradation efficiency of >95 %. Chain cleavage is achieved through the decarboxylation of the N-hydroxyphthalimide ester and subsequent ß-scission of the backbone radical. Electrochemistry is thus shown to be a powerful tool in selective polymer transformations and controlled macromolecular degradation.

Gradient Copolymer Synthesis through Self-Assembly.

Polymerization-induced self-assembly (PISA) is typically performed to produce polymer nanoparticles featuring specific assembly morphologies. Herein, we demonstrate the use of PISA as a synthetic tool to direct gradient copolymer synthesis. Specifically, we leverage hydrophobicity-induced reaction selectivity and the rate acceleration typically associated with polymer compartmentalization upon assembly during PISA to bias reaction selectivity. In the chain extension of a poly(ethylene glycol) macrochain transfer agent, the selectivity of diacetone acrylamide (DAAm) and N,N-dimethylacrylamide (DMA), two monomers with near-identical reactivity in water, can be modulated in situ such that DAAm is preferentially incorporated over DMA upon self-assembly. By increasing the feed ratio of DAAm, monomer differentiation can be further biased toward DAAm due to the locus of polymerization becoming increasingly hydrophobic. This change in selectivity affords the autonomous generation of DAAm-DMA gradient sequences, otherwise inaccessible without outside intervention. Finally, a mild hydrolysis protocol can then be employed to harvest DAAm-DMA sequences, yielding compositionally unique gradient copolymers.

Backbone Degradation of Polymethacrylates via Metal-Free Ambient-Temperature Photoinduced Single-Electron Transfer.

Polymeric materials comprised of all-carbon backbones are ubiquitous to modern society due to their low cost, impressive robustness, and unparalleled physical properties. It is well-known that these materials often persist long beyond their intended usage lifetime, resulting in environmental accumulation of plastic waste. A substantial barrier to the breakdown of these polymers is the relative chemical inertness of carbon-carbon bonds within their backbone. Herein, we describe a photocatalytic strategy for cleaving carbon-based polymer backbones. Inclusion of a low mole percent of a redox-active comonomer allows for a dramatic reduction in polymer molecular weight upon exposure to light. The N-(acyloxy)phthalimide comonomer, upon reception of an electron from a single-electron transfer (SET) donor, undergoes decarboxylation to yield a backbone-centered radical. Depending on the nature of this backbone radical, as well as the substitution on neighboring monomer repeat units, a ß-scission pathway is thermodynamically favored, resulting in backbone cleavage. In this way, polymers with an all-carbon backbone may be degraded at ambient temperature under metal-free conditions.

Modular Genetic Code Expansion Platform and PISA Yield Well-Defined Protein-Polymer Assemblies.

We present a modular platform from which biohybrid protein-polymer nanostructures can be generated in a straightforward and facile manner. Specifically, an aqueous polymerization-induced self-assembly (PISA) AB block copolymerization system was derived from a mutant superfolder green fluorescent protein (sfGFP) as the solvophilic, stabilizing A block. By genetically encoding sfGFP with an isobutyryl bromide functionality, we grafted a quintessential atom-transfer radical polymerization initiation site with hydroxypropyl methacrylate (HPMA) to form the solvophobic B block. Monitoring nanostructure formation using dynamic light scattering, gel permeation chromatography, and transmission electron microscopy revealed uniform micellar morphologies. The radii of the micelles increased with increasing HPMA block length, resulting in nanoparticle sizes ranging from 15 to 48 nm. Solvophilic stabilization afforded by the encoded sfGFP makes this an ideal PISA initiator, and we posit this platform has potential for generating complex biohybrid nanostructures for other protein-polymer systems.