Self-healing polymers prepared via living radical polymerisation

Diels-Alder chemistry has been used to synthesise polymerisation initiators and a dimethacrylic crosslinker 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).