Photoinduced raft polymerization from novel water-soluble single-chain nanoreactors

Abstract

Single chain nanoparticles (SCNPs) are ultra-small size nano-objects, which are obtained by the collapse of a single polymer chain. In the literature, there are many examples of potential SCNPs for a range of applications such as biomedicine, catalysis or sensing.1,2,3 In principle, these nanomaterials could be easily tuned, creating new materials with exceptional properties to be used in novelty applications such as photocatalysis.4 Only few works describe the use of SCNPs as photocatalyst, being the control of the reaction the most challenging point. In this project, we described the preparation of new SCNPs with promising properties to be used as photocatalyst in Reversible Addition Fragmentation Chain Transfer (RAFT) polymerization of N-isopropylacrylamide (NIPAM) in water. These photocatalysts, based on SCNPs, were synthesized starting from an amphiphilic copolymer of 2-acetoacetoxy ethyl methacrylate (AEMA, hydrophobic monomer) and oligo(ethylene glycol) methyl ether methacrylate (OEGMA, hydrophilic monomer). Through a post-functionalization of the copolymers, we prepared Iridium-decorated amphiphilic SCNPs (SCNPs-Ir). In order to have a first evaluation of the photocatalytic performances of SCNPs-Ir, we choose the aqueous photopolymerization of NIPAM as a model reaction. The efficiency of the polymeric photocatalyst was then compared with an unsupported Iridium catalyst, which if employed in the same reaction conditions, led to poor results in terms of mass yield and polydispersity of the final products (Poly(NIPAM), (PNIPAM)). When using SCNPs-Ir as the photocatalyst, we isolated way better polymerization products (PNIPAMs), in agreement with the typical behaviour of a classical controlled radical polymerization (CRP). In all cases, the products obtained from the photopolymerization reactions were characterized using different experimental techniques, including gel permeation chromatography/size exclusion chromatography (GPC/SEC), dynamic light scattering (DLS) and proton nuclear magnetic resonance (1H NMR).