Effect of poly(ɛ-caprolactone) in polybenzoxazine blends and respective copolymers on morphology and mechanical properties

Covalent and non-covalent incorporation of poly(ɛ-caprolactone) (PCL) in a bisphenol A based benzoxazine (BA-a) yields copolymer and blend-type PCL/PBA-a polymers differing in their properties depending on their bonding state. Gel content and morphology studies revealed that in case of unbound PCL a threshold between 20 and 30 wt-% of PCL exist showing a partial miscibility below and phase separation above that critical value giving opaque and partially crystalline samples. Tosylated PCL binds to a certain extent covalently into PBA-a's network yielding a homogenous polymer at low PCL contents, but a mixed bonding mode of copolymer and blend like structures with increasing PCL content. The polymerization behavior, thermomechanical properties and resulting morphologies of copolymers were studied and compared to analogue PCL/polybenzoxazine blends. Tensile tests proved that 10 and 20 wt-% of covalently incorporated PCL entail toughening of the brittle benzoxazine increasing ultimate tensile strength by 43% and elongation at break by 130%, simultaneously.