The aim of this study was to examine possible effects of the hydroxyl group (-OH) in phenoxy-type polymers on the cure reactions and network morphology of a crosslinking epoxy system, tetraglycidyl-4,4＇-diaminodiphenylmethane (TGDDM) with diaminodiphenylsulfone (DDS). Similar to the case for a pure, unmodified TGDDM/DDS epoxy counterpart, an autocatalytic reaction kinetic model was found to describe the cure behaviour of the phenoxy/TGDDM/DDS mixtures up to the vitrification point. At the early stage of cure, the -OH group in the phenoxy might exert a catalytic effect for epoxide ring opening between epoxy and the amine. Subsequently, at later cure stages where phase domain boundaries were forming and the amine groups were largely depleted, the -OH groups of the phenoxy phase domain began to react with the residual epoxide groups in the epoxy domains. It is this later-stage reaction that led to interlinking chemical bonding between the phenoxy and epoxy phases at the domain boundaries.