Confined crystallization and degradation of six-arm star PCL with core of cyclotriphosphazene in epoxy thermosets

Six-arm star polycaprolactone with core of cyclotriphosphazene (s-PCL) was synthesized via ring-opening polymerization and characterized by NMR and GPC. Epoxy thermosets incorporating 10-40 wt% of this copolymer were cured with 4,4'-methylenebis(2-chloroaniline) (MOCA) and 4,4'-diaminodiphenyl sulfone (DDS), respectively. In these thermosets, intermolecular specific interactions had a significant impact on their morphologies. Specifically, no discernable macroscopic phase separation was found in FESEM images of MOC-Acured epoxy resins. However, for the DDS-cured system, s-PCL was partially miscible with the epoxy thermosets, as evidenced with FTIR and DMA. This is may be owning to enriched concentration of hydroxyl groups in the s-PCL favored the miscibility between PCL subchains of carbonyl and the epoxy matrix. Dispersed phase, further confirmed by XRD to be amorphous, with a diameter of 0.34-0.44 pm could be observed (s-PCL' content <= 20 wt %) in this system. Nevertheless, crystallization of PCL could not be suppressed completely (s-PCL' content > 30 wt%). Besides, epoxy thermosets containing crystalline PCL were found to be more resistant to thermal degradation but sensitive to alkaline degradation (10% NaOH aqueous solution) according to TGA and FESEM results. This work presented here is a meaningful report on the presence of alkaline-labile crosslinking points through the whole networks.