Phase separation behaviour has been investigated for composite films made of the nematic mixture E7 embedded in a thermoplastic matrix of PBMA or PMMA. Different approaches, based on optical and calorimetric analyses, have been applied to PDLC films, prepared by solvent coating techniques followed by thermal treatments, in order to determine the solubility limit of E7 in the matrices and the fraction of LC contained within the segregated domains. The two systems exhibit distinct mechanisms of phase separation : nucleation and growth occurs in PBMA/E7, whereas PMMA/E7 separates through spinodal decomposition. PBMA/E7 composites, because of the low Tg of the polymer and the high solubility of the LC in the matrix at room temperature, seem to be unsuitable for PDLC application; a higher degree of phase separation characterizes the PMMA-based films. Preliminary electro-optic properties have been investigated on the latter system.