Self-healing polymers prepared via living radical polymerisation

Abstract

Diels–Alder chemistry has been used to synthesise polymerisation initiators and a dimethacrylic cross-linker that leads to efficient cleavage and reformation; self-healing. The initiators were prepared using 1-(2-hydroxyethyl)-1H-pyrrole-2,5-dione (3) as an intermediate, and reacting this with furfuryl alcohol to afford 2-bromo-2-methyl-propionic acid 2-[1-(2-bromo-2-methyl-propionyloxymethyl)-3,5-dioxo-10-oxa-4-aza-tricyclo[5.2.1.02,6]dec-8-en-4-yl]-ethyl ester (7) and 9-anthracenemethanol to yield initiator (8). The former exhibited polymers with excellent cleavage properties (M_n 12 000 g mol⁻¹ to 6500 g mol⁻¹) with reformation at efficiency of 50% (M_n 8900 g mol⁻¹). The initiator from the anthracene derivative initially indicated that retro-Diels–Alder was not occurring with no change in the NMR or GPC data. An excess of a rhodamine-based dienophile was added to capture any cleaved anthracene-terminated polymer, with results indicating that the polymer is cleaving and reforming upon the cooling cycle. Similar results were observed with arm first stars, made using a Diels–Alder based dimethacrylate cross-linker. Little cleavage was observed initially, however, addition of the tag gave a significant reduction in M_w (7080 g mol⁻¹ to 5300 g mol⁻¹) and M_w/M_n (1.78 to 1.26).