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Polymer-dispersed liquid crystals (PDLCs), consisting of a dispersion of LC-rich domains in a polymer matrix, are used in different types of electrooptical devices. Their efficiency can in principle be increased if the LC domains exhibit a uniform characteristic size in the range of the wavelength of visible light. In an attempt to generate this type of morphology, a model PDLC system based on a 50 wt % solution of N-4-ethoxybenzylidene-4‘-n-butylaniline (EBBA) in an epoxy monomer (diglycidyl ether of bisphenol A, DGEBA) was analyzed. The polymerization-induced phase separation was performed at 80 °C, using a tertiary amine as initiator (benzyldimethylamine, BDMA). By selecting an initial concentration located close to the critical composition to promote spinodal demixing, co-continuous morphologies were obtained, which were rapidly fixed by gelation. The conversion of epoxy groups (p) was followed by near-infrared spectroscopy (NIR). At p = 0.28, phase separation took place as revealed by transmission optical microscopy (TOM) and by the acceleration observed in the isothermal cure rate. Gelation took place at p = 0.35, soon after the cloud point. Although the primary structure was arrested by gelation, the LC-rich phase was continuously enriched in pure EBBA, as revealed by the increase in T NI with conversion monitored by differential scanning calorimetry (DSC). Co-continuous structures remained unmodified after the storage of PDLCs for several months. The nematic range of the LC-rich phase at p = 1 was comprised between 34 °C (melting point) and T NI = 68 °C. A 57% of the initial LC was present in nematic domains at 40 °C, as determined by the variation of the FTIR absorbance of a characteristic LC peak between isotropic and nematic states. Therefore, a possible route to obtain PDLCs with a uniform characteristic size of LC domains is to start with a composition close to the critical one and select conditions to produce liquid−liquid demixing soon before gelation.

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Summary: Reactions taking place in a homogeneous solution of an epoxy monomer based on the diglycidyl ether of bisphenol A (DGEBA) and palmitic acid (PA), in the presence of benzyldimethylamine (BDMA), were investigated using Fourier‐transformed infrared spectroscopy (FTIR) and size exclusion chromatography (SEC). In the stoichiometric formulations prepared with equal molar ratios of epoxy (E) to carboxyl groups, E/PA = 1, the main reaction was the carboxyl addition to the epoxy giving a β‐hydroxy ester. This reaction was followed by transesterification that occurred to a very small extent. In the formulations prepared with an epoxy excess, E/PA > 1, the transesterification reactions were very significant as well as the homopolymerization of the epoxy excess that took place to an almost complete conversion. Reaction products synthesized in the range of 1 < E/PA < 2 were solids at room temperature due to the crystallization of a fraction of fatty acid chains. Above the melting temperature, reaction products recovered the liquid state. The formulation synthesized with E/PA = 2 exhibited a good behavior as a hot‐melt adhesive of steel sheets with a single lap‐shear strength of 2.5 MPa and an interfacial‐cohesive failure. For E/PA > 3, the gelation took place leading to the networks exhibiting a single glass transition temperature (Tg) without any evidence of crystallization or phase separation. Tg varied from 90 °C for the neat epoxy to 0 °C for the formulation with E/PA = 3.Single lap‐shear strength values of hot‐melt adhesives corresponding to reaction products synthesized with E/PA = 1.6, 1.8, and 2.magnified imageSingle lap‐shear strength values of hot‐melt adhesives corresponding to reaction products synthesized with E/PA = 1.6, 1.8, and 2.