Hard confinement systems as effective nanoreactors for in situ photo-RAFT: towards control over molecular weight distribution and morphology

Abstract

This work highlights the development of a robust and universal route towards gaining control over macromolecule molecular weight, molecular weight distribution and, more importantly, morphology through the implementation of photoiniferter-mediated RAFT (photo-RAFT) carried out using mesoporous materials varying in the composition, pore arrangement, and pore diameters (metal–organic framework SBA-15 powder d = 5–15 nm, silica SiO₂ templates d = 4 nm, alumina oxide AAO templates d = 10 nm). In fact, the application of these matrices that can act as nanoreactors for in situ UV-irradiated photo-RAFT of both commercial methyl methacrylate (more-activated monomer) and the synthesized N-vinyl-1,2,4-triazolium-based ionic liquid (less-activated monomer) is a key aspect of our approach. The collected data allowed us to probe the influence of the structural features of nanoreactors (i.e., transparency, porosity, roughness, and acidity) as well as confinement-related effects connected to variation in free volume and surface interactions on the polymerization path and properties of the produced ionic and non-ionic polymers. It was found that the application of all tested nanoreactors ensures greater control over photo-RAFT than analogous batch systems (macroscale photo-RAFT). However, running the reaction in mesoporous AAO templates offered by far the best control over the course of photo-RAFT of both the less-activated monomer (LAM) and the more-activated monomer (MAM) irrespective of the type of selected RAFT agent (switchable) (carbamodithioate vs. trithiocarbonate), their properties and, more importantly, the yield of the recovered polymers.