Fully photodegradable block copolymer nanoparticles for dual release of cargo and radicals

Abstract

When exposed to radiation, photo-responsive block copolymer nanoparticles disassemble to liberate a possible carried guest. However, the particle disruption is rarely accompanied by a polymer chain disintegration into molecular fragments, that would facilitate clearance from the body. We describe herein a novel class of fully photodegradable all-acrylic poly(hydroxyethyl acrylate)-b-poly(o-nitrobenzyl acrylate) (PHEA-PNBA) nanoparticles. Their synthesis proceeds by dispersion polymerization-induced self-assembly (PISA) based on a reversible addition–fragmentation chain transfer mechanism. The self-immolation mechanism is initiated via a dual H-abstraction by the electronically excited o-nitrobenzyl pendant group, first, from the adjacent CH2, second, from CH of the polyacrylate chains. The former results in the release of the protecting group, while the latter initiates a cascade of reactions that fragment the whole polymer backbone. Simultaneous chain scission and cleavage of o-nitrobenzyl group combine in turn to induce a fast and complete degradation of the copolymer particles. Synthesis, structural and colloidal characterization of the diblock copolymer nanoparticles, photochemical mechanism governing self-immolation are described. Emphasis is placed on understanding the reaction parameters which are important in controlling degradation rates, in particular nature of continuous phase and degree of polymerization of the PNBA block. UV exposure is exploited to release a model guest (Nile red) from the particles. Additionally, the burst release of free radicals accompanying the chain degradation can serve to decompose a target molecule (methylene blue).