Vinyl mercaptoethanol as a reactive monomer for the preparation of functional homo- and copolymers with (meth)acrylates

Abstract

In contrast to common more activated monomers (MAMs), such as (meth)acrylates or styrenes, vinyl thioethers remain a niche, despite their unique character featuring an electron rich vinyl moiety, which in contrast to vinyl ethers still enables good stabilization of a propagating radical. The sulfur-group further induces a variety of unique properties, for example, the ability to coordinate metals or increase the refractive index, but their limited availability certainly remained a major bottleneck in a wide range of applications of these monomers. Based on recent progress in the direct vinylation of mercaptans, we here demonstrate that vinyl mercaptoethanol (VME) represents a scalable reactive building block for the preparation of functional homo- and copolymers. The former are easily accessible by radical polymerization resulting in transparent, soft and very adhesive homopolymers with enhanced refractive indices compared to other non-aromatic polymers. The high density of hydroxyl groups renders the polymers polar and only soluble in corresponding solvents, but not in water. Only the further oxidation of the sulfide moiety to the more polar sulfoxide creates a water soluble and even slightly hygroscopic polymer. Copolymerizations of VME with common MAMs confirmed previous reports on the Q- and e-values of comparable vinyl thioethers and statistical copolymers with electron deficient vinyl monomers such as n-butylacrylate (BA) or methyl methacrylate (MMA) can be prepared with a tendency towards an alternating sequence. The resulting copolymers were tested for their optical and mechanical properties. The comparable reactivity of the radicals further facilitates the preparation of defined homo- and (block) copolymers with tunable lengths by the reversible addition fragmentation chain transfer (RAFT) process. Overall, the various reactivities of VME and the good compatibility with other MAMs in radical polymerizations render this industrially producible monomer certainly attractive for future materials design.