Preparation and experimental studies on the phase transitions and morphology of novel polymer-dispersed liquid crystal (PDLC) mixtures of polysulfone UDEL-3000 (PSU) or its derivatives (chloromethylated polysulfone or polysulfone containing lateral phosphaphenanthrene substituent) and a phosphorus-containing liquid crystalline polymer (LCC) that exhibit isotropic/nematic/smectic-A mesophase transition were performed. The mesomorphic properties of PDLC have been investigated by differential scanning calorimetry and polarizing optical microscopy. Mesophases structures were also investigated by X-ray diffraction measurements, the diffraction pattern being in close dependence on the polysulfone structure and PDLC composition. The effect of the phosphorus content on the thermal properties was evaluated by thermogravimetric analysis. The results reveal that the composites were stable up to 337°C in air showing initial decomposition temperatures in the range of 337–368°C and a 10% weight loss in the range of 357–397°C. The presence of P in the structure of LCC leads to higher char yields at 700°C, for PDLCs composites, increasing with the content of phosphorus-containing polymer. POLYM. ENG. SCI., 2013. © 2012 Society of Plastics Engineers