Reaction routes with glycidyl methacrylate for the incorporation of oleic acid in amphiphilic block copolymers

Abstract

This research focused on assessing different reaction routes for synthesizing amphiphilic block copolymers, with the hydrophobic part built using glycidyl methacrylate and oleic acid and the hydrophilic segment made from 2-(dimethylamino)ethyl methacrylate. The main objectives of this study were to identify reaction routes leading to low-impact branching and/or crosslinking mechanisms involving epoxides and oleic acid, and to synthesize p(GMA-OA)-b-p(DMAEMA) copolymers in a simple and scalable manner. Block copolymer synthesis was considered using both ATRP and RAFT polymerization.

The reaction route involving the synthesis of methacrylated oleic acid proved problematic, whereas higher synthesis efficiency was achieved when the glycidyl methacrylate moieties were modified with oleic acid after polymerization. It was found that working with DMSO solvent and a stoichiometric excess of oleic acid was particularly important for reducing branching/crosslinking. FTIR and GPC analyses were used to assess the progress of the chemical composition and molecular architecture of the intermediate homo- and co-polymers, and to demonstrate the successful production of the intended p(GMA-OA)-b-p(DMAEMA) materials.

The synthesized block copolymers were used for encapsulating and delivering oleanolic acid considering solid polymer dispersions and aqueous particle dispersions. SEM and TEM analysis demonstrate the ability of the p(GMA-OA)-b-p(DMAEMA) copolymers to self-assemble in an aqueous environment and well-defined spherical aggregates were observed, for example with size up to 100 nm in size with an external shell around 5–8 nm thick. A high loading capacity for oleanolic acid was measured, with a range of up to 0.17 mg/mL in aqueous particle dispersions. The dynamics of oleanolic acid release was measured under different conditions, including changes in solvent composition, pH and temperature. The results demonstrate sustained release of the encapsulated oleanolic acid and transitions induced by pH/temperature changes.