UV-degradable poly(phenyl vinyl ketone) particles produced by polymerisation-induced self-assembly in ethanol or water

Abstract

Degradable polymer nanoparticles are attracting increasing interest for applications in cargo-release and imaging, as well as offering degradable alternatives to non-degradable nanoparticles used in various commodity applications. One promising approach is the utilisation of photo-degradable polymers such a poly(vinyl ketones). Here we report the ethanolic dispersion and aqueous emulsion polymerisation-induced self-assembly (PISA) of phenyl vinyl ketone (PVK) using a linear polyethylene glycol macromolecular reversible addition-fragmentation chain transfer (RAFT) agent (PEG5K-TTC) to produce UV-light degradable block copolymer (PEG5k-b-PPVK) nanoparticles. We demonstrate that photo-RAFT PISA in ethanol produces well-defined PEG5k-b-PPVK spherical nanoparticles (D_z = 36 – 101 nm) with high monomer conversions in 2 h. These nanoparticles were found to readily degrade under UV-light irradiation, and in natural sunlight, with a substantial loss in molar mass (26 to 1 kg.mol^-1). SAXS and TEM studies demonstrated that degradation in ethanol led to a complete loss of the nanoparticle structure. However, upon degradation in water, the particle structure was maintained, although chain degradation occurred as well; presumably because the formed hydrophobic PPVK fragments remain assembled in the hydrophobic particle core due to their insolubility in water. Aqueous emulsion thermal and photo-RAFT PISA of PVK were also studied to produce degradable aqueous diblock copolymer latexes. Utilisation of a photo-RAFT polymerisation procedure led to unwanted side reactions attributed to the production of light-generated monomer radicals, which can initiate a free-radical polymerisation within the monomer droplets. However, utilisation of a classical thermal-RAFT polymerisation avoided this competing initiation and generated well-controlled PEG-b-PPVK diblock copolymers. Lastly, the possibility to copolymerise styrene with PVK through an aqueous emulsion PISA was also demonstrated. All aqueous latexes also showed significant polymer degradation when irradiated with UV-light. This work demonstrates how UV-degradable diblock copolymer nanoparticles can be efficiently synthesised via PISA in both ethanol and water.