Self-organized thermosets involving epoxy and poly(ɛ-caprolactone)-block-poly(ethylene-co-ethylethylene)-block-poly(ɛ-caprolactone) amphiphilic triblock copolymer

In this work, we investigated the self-assembly behavior of poly(ɛ-caprolactone)-block-poly(ethylene-co-ethylethylene)-block-poly(ɛ-caprolactone) (PCL-b-PEEE-b-PCL) triblock copolymer in epoxy thermosets. The PCL-b-PEEE-b-PCL triblock copolymer was synthesized via the ring-opening polymerization of ɛ-caprolactone with a hydroxyl-terminated poly(ethylene-co-ethylethylene) as the macromolecular initiator. The hydroxyl-terminated poly(ethylene-co-ethylethylene) was prepared with the hydrogenation reaction of a hydroxyl-terminated polybutadiene. The triblock copolymer was incorporated into the precursors of epoxy to obtain the nanostructured thermosets. It was found that the self-organized nanophases were formed in the mixture before curing reaction and the nanostructures can be further fixed via curing reaction. The self-assembly behavior of the triblock copolymer in epoxy thermosets was investigated by means of atomic force microscopy (AFM), small-angle X-ray scattering (SAXS) and dynamic mechanical thermal analysis (DMTA). Differential scanning calorimetry (DSC) shows that the formation of the self-organized nanophase in the thermosets caused that a part of poly(ɛ-caprolactone) subchains were demixed from epoxy matrix with the occurrence of curing reaction; the fractions of demixed PCL blocks were estimated according to the Tg-composition relation of the model binary blends of epoxy and PCL.