Covalent grafting of functional oligo-isoprenes onto silica-based surfaces to achieve robust elastomeric monolayers, thin films and coatings

Abstract

A new methodology is presented to covalently graft polyisoprene from natural or recycled rubber on hydroxylated and silicon-containing surfaces. For this purpose, we first synthesized novel functional telechelic oligomers from natural rubber, bearing a hydroxyl group at one chain end and a silane group at the other, which allowed their direct tethering on silicon-based and other materials. As alternative approach, we also synthesized bi-functional telechelic oligomers with a ketone and an aldehyde end-moieties and they reacted selectively with surface amino groups, introduced via a pre-functionalization step using commercial amino-alkoxysilanes. A high glass surface coverage density was reached and the oligoisoprenes free chain-ends were converted to acrylate functions, to possibly grow more polymer or to engage a photopolymerization process with other bio-based acrylate-terminated telechelic oligoisoprenes, in order to obtain thick films. In this way, ultra-thin oligomer layers, copolymer brushes, as well as grafted films and bulk materials were formed and characterized at sub-nanometer resolution using X-rays Reflectivity. A strong covalent grafting of polyisoprene coatings was achieved and resisted to long immersions in water and aggressive organic solvents under strong mechanical agitation. The robust molecular, thin films, and bulk sheathings are versatile polymeric constituents and represent a new family of sustainable coatings.