Six-arm star-shaped polymer with cyclophosphazene core and poly(ε-caprolactone) arms as modifier of epoxy thermosets

A six-arm star-shaped poly( ε -caprolactone) (s-PCL) based on cyclophosphazene core was obtained by presynthesis of a hydroxy-teminated cyclophosphazene derivative and subsequent initiation of the ring-opening polymerization of ε -caprolactone, and its use in different proportions as toughening modifier of diglycidylether of bisphenol A/anhydride thermosets was studied. The star-shaped polymer was characterized to have approximately 30 caprolactone units per arm. Differential scanning calorimetry revealed a nonsignificant influence on the curing process of the epoxy-anhydride formulation by the addition of s-PCL. The s-PCL-modified epoxy thermosets exhibited a great improvement in both toughness and strength compared with the neat resin, as the result of a joint effort by the internal rigid core and the external ductile polyester chains of s-PCL. When the addition of the modifier was 3 wt %, an optimal mechanical and thermomechanical performance was achieved. The impact resistance and tensile strength of the cured epoxy resin were enhanced by 150% and 30%, respectively. The glass transition temperature was also increased slightly. Moreover, the addition of the star-shaped modifier had little harmful effect on the thermal stability of the material. Thus s-PCL was proved to be a superior toughening agent without sacrificing thermal and mechanical properties of the thermosets. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134 , 44384.