Investigation and optimization of surface modification protocols to attach sequence defined oligomers onto silica substrates

Abstract

Sequence defined (SD) oligomers are synthesized by single unit monomer insertion controlled radical polymerization (SUMI-CRP) and elaborate purification which is holding back the development. Multiple hydrogen bond (MHB) SD oligomers are similar to biopolymers since they recognize their complementary part. This ability can be exploited by covalently grafting these oligomers onto silica substrates and therefore simplify the purification. For a proof of principle study grafting of SD oligomers onto silica particles is investigated. SD acrylate trimers are obtained by RAFT or photo-CMP polymerization. The statistical mixtures are purified by column- or size exclusion chromatography. Piranha treatment proved to be unnecessary to obtain sufficient grafting densities (0.331 CPTMO groups/nm²). SD oligomers and functionalized silica particles are linked with EDC/NHS coupling or copper azide-alkyne click (CuAAC) chemistry and characterized with TGA. The results show that synthesizing SD oligomers with DoPAT RAFT agent is not recommended since the acid groups stick to chromatographic columns, deteriorating purification. More promising is using CPD-TCC agent, followed by trithiocarbonate modification and attachment of the alkyne SD oligomers with CuAAC onto azide-silica (0.082 oligomer groups/nm²). Also, SD oligomers synthesized by photo-CMP is successful (17.38% yield of MA-EA-EHA-Ebib). The bromides are modified into azides and grafted-to alkyne-silica (0.177 oligomer groups/nm²). As outlook, MHB SD oligomers can be investigated.