Novel semi-interpenetrating polymer networks (so-called simultaneous SIPNs) of various compositions were synthesized using segmented polyurethane Urea (SPUU), N-isopropylacrylamide (NIPAM), acrylic acid (AA), and butyl methacrylate (BMA), resulting in an SIPN film denoted as SPUU/poly(NIPAM-co-AA-co-BMA). The resulting simultaneous SIPN films were neutralized by exposure to pH 7.4 phosphate buffer solution (PBS). The neutralized films were dried and then characterized by differential scanning calorimetry (DSC). The DSC results showed that the T-g of the SIPNs depends mostly on SPUU content and on the composition of the acrylate monomers. PNIPAM was incorporated as a second network in one composition of simultaneously prepared SIPN film through a sequential polymerization method (so-called sequential SIPNs). Both simultaneous and sequential SIPN films were examined by scanning electron microscopy (SEM) after freeze drying at their equilibrium states. The SEM Study revealed that simultaneous SIPNs had a porous morphology in the absence of BMA, but the porosity disappeared at higher BMA content. The morphology of the sequential SIPN film was almost similar to that of pure PNIPAM. Finally, simultaneous and sequential SIPNs were used for swelling and drug release studies at different pH values and at different temperatures to determine the environmental sensitivity of these gels. Simultaneous SIPNs absorbed more water than sequential SIPNs, but both had a poor rate of water absorption at pH 1.2. In the drug release study, a higher thermosensitivity, was observed for sequential SIPNs than for simultaneous SIPNs. (C) 2009 Elsevier Ltd. All rights reserved.