Crosslinking of poly(ethylene-co-vinyl alcohol) with diphenylboronic acid of tetraphenylethene enables reprocessing, shape recovery and photoluminescence

A novel diphenylboronic acid carrying tetraphenylethene moiety (BO-TPE-BO) was synthesized and used to crosslink poly(ethylene-co-vinyl alcohol) (EVOH). The crosslinking reaction occurred between 1,3-diol structural units of EVOH and diphenylboronic acid groups of BO-TPE-BO. The crosslinking densities increased with raising the contents of BO-TPE-BO. Owing to the crosslinking, the thermomechanical properties were significantly improved in terms of glass transition temperatures (Tg's), Young's moduli and tensile strengths. More importantly, the EVOH-TPE networks can be reprocessed (or recycled) via the dynamic exchange of boronic ester bonds. In addition, the EVOH-TPE networks can display the shape memory properties. Through the dynamic exchange of boronic ester bonds, the original shapes of the shape memory polymers were reconfigurable. Thanks to the introduction of tetraphenylethene moieties, the EVOH-TPE networks can additionally display the photoluminescent properties. It was found that the photoluminescent behavior was quite dependent on the crystallinity and the contents of BO-TPE-BO.