Azopolymers are highly versatile materials due to their unique photoresponsive properties. In this contribution, a novel azo‐modified epoxy network is synthesized by cationic homopolymerization with ...boron trifluoride monoethylamine (BF3.MEA) complex as initiator. The effect of the addition of a fixed content of amino‐functionalized azo chromophore, Disperse Orange 3, into the polymer matrix is studied in detail. First of all, the thermal curing cycle is optimized by means of differential scanning calorimetry (DSC) and Fourier transform infrared spectroscopy (FTIR) measurements. Then, the resulting bulk azo‐modified epoxy networks are characterized by means of thermogravimetric analysis (TGA), FTIR, DSC, UV–vis spectroscopy, and rheological measurements. Finally, the optical response of thin films of these materials is determined. The results evidence that azo‐modified epoxy networks obtained by cationic polymerization with optimized curing cycle display high Tg values, high maximum photoinduced birefringence, fast writing speed, and exceptionally high remnant anisotropy. Therefore, this material is a promising candidate to be used for optical storage applications.
A new type of azo‐modified epoxy network has been prepared by the way of cationic homopolymerization with boron trifluoride monoethylamine (BF3·MEA) complex as initiator. The resulting networks are promising materials for optical storage applications.
Azobenzene containing epoxy networks are a class of photosensitive materials characterized by high thermal, optical and mechanical stability, promising for reversible optical storage applications. ...Here, we propose an encouraging two-step method to fabricate crosslinked coatings by simply reacting an amine-functionalized azobenzene and an epoxy resin in bulk for specified times to get soluble products (network precursors). Thin films based on these precursors were prepared, and thermally crosslinked in order to obtain high-Tg materials. The optical response of the materials was determined, both before and after crosslinking. In the case of the samples as prepared, the dynamic time response of the system is fast, as well as the relaxation of the photoinduced birefringence, as expected due to the high mobility of the chromophore. On the other hand, crosslinked systems have a slightly slower response, but higher values of remnant birefringence, providing stability of the photoinduced orientation, what makes them promising materials to use in optical storage applications. Besides, further analysis on the effect of temperature on the induced birefringence of the polymeric networks was also conducted to help optimization of material design. Finally, we had presented some preliminary investigations of surface relief grating recording in the obtained new materials.
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Blends of polystyrene (PS) with an epoxy monomer (DGEBA) and a tertiary amine (BDMA), were initially miscible at 120°C but phase‐separated at very low conversions in the course of polymerization. ...Although there was a significant difference between the refractive indices of polystyrene and the DGEBA/BDMA solution, the refractive index of the epoxy network increased in the course of polymerization, attaining a value close to that of PS at complete conversion. A sharp decrease of the light transmittance was observed at the cloud‐point, observed at very low conversions. However, the continuous increase of the refractive index of the epoxy phase with conversion produced an approximate matching of both refractive indices, leading to transparent materials at complete conversion. Morphologies generated by reaction‐induced phase separation depended on the molar mass distribution of polystyrene and its mass fraction in the blend. For a PS with a high value of the mass‐average molar mass (Mw), it was possible to generate a dispersion of PS particles in the epoxy matrix (blends containing 5 wt% PS), phase‐inverted morphologies (blends containing 15 wt% PS) and double‐phase morphologies (blends with 10 wt% PS). Therefore, PS/DGEBA/BDMA blends could be used to obtain transparent epoxy coatings toughened by polystyrene particles or transparent polystyrene parts reinforced by a dispersion of epoxy particles.
As an example of thermoplastic/liquid crystal blends that do not exhibit a liquid‐liquid immiscibility region in their phase diagrams, a polystyrene (PS)/N‐4‐ethoxybenzylidene‐4′‐butylaniline (EBBA) ...blend was analyzed. The complete phase diagram was built up using thermal transitions determined by differential scanning calorimetry (DSC) and polarized optical microscopy (POM). The boundary of the nematic + isotropic region was fitted with the Flory‐Huggins‐Maier‐Saupe model, extended to consider the polydispersity of PS. Main factors controlling the morphologies generated by thermal‐induced phase separation (TIPS) were the initial EBBA concentration in the blend and the cooling rate. Cooling at a fast rate led to small nematic domains with a narrow size distribution. Slow cooling rates led to the coexistence of very large and small dispersed domains. This was because of the large extent of coalescence of the droplets first generated associated with the continuation of the nucleation/growth process in a medium of increasing viscosity. The use of fast cooling rates might be important for the generation of a narrow size‐distribution of nematic droplets by TIPS in polymer‐dispersed liquid crystals (PDLC) used in electrooptical devices.
Micrograph obtained by transmission optical microscopy without crossed polarizers, showing nematic domains dispersed in a glassy matrix arising by a fast cooling of the blend from 130 °C; composition of blend: 70 wt.‐% EBBA.
