Pseudo-thermoplastic interpenetrating polymer networks (p-TIPNs) prepared by mechanical mixing of a crystallizable polyurethane (CPU) and styrene/acrylic acid random copolymer (S/AA) were characterized by specific heat capacity measurements in the temperature interval 133-433 K, as well as by wide-angle and small-angle X-ray scattering. It was established that: 1. Crystallizability of BAG is the main cause of microphase-separated morphology of CPU. 2. Limited miscibility of CPU with S/AA significantly affects the phase morphology of p-TIPNs on their base. Mixed microphase of fixed composition [CPU/(S/AA) = 90/10] and essentially pure microphase of S/AA are the main structural entities in as-quenched samples of p-TIPNs of whatever nominal composition. More complex phase morphology (that is, coexistence of essentially pure microphases of crystallized BAG and of S/AA, and of the mixed CPU/(S/AA) microphase enriched with S/AA) is expected for initial samples.