Activated anionic ring-opening polymerization for the synthesis of reversibly cross-linkable poly(propylene oxide) based on furan/maleimide chemistry
The synthesis of cross-linkable random copolyethers of propylene oxide (PO) and furfuryl glycidyl ether (FGE) is first discussed. The anionic ring-opening polymerization and monomer activation methodology, based on the combination of tetraoctylammonium bromide and triisobutylaluminum, is used to perform the controlled synthesis of poly(propylene oxide-co-furfuryl glycidyl ether) copolymers with various compositions 95/5, 90/10, 75/25, 50/50, and 25/75 (PO/FGE mol%) and keeping the furfuryl moieties active. Copolymers with molar masses around 10 000 g mol−1 were obtained in short times. Subsequently, the furfuryl moieties were reacted with aromatic and aliphatic maleimide-based cross-linkers to perform Diels–Alder (DA) “click” reactions. Three-dimensional networks were obtained and their swelling ratio and insoluble fraction were determined. Glass transition temperature and retro-Diels–Alder (rDA) transition in the network were determined by differential scanning calorimetry analyses. Gel properties vary with the furan group amount in the initial copolymer and the cross-linker structure. The network disassembly at 110 °C was monitored by 1H NMR and quantitatively recorded by the re-appearance of the copolymer signals due to the rDA reaction. The solubility study showed that the gel was able to reform at 20 °C leading to reversible cross-linked polyethers.