Repositori URV

Identifier: TDX:763

Handle: https://hdl.handle.net/20.500.11797/TDX763

Authors:
Ribera Ruiz, David

Abstract:
The search for new materials with unusual mechanical and thermal properties led to research into liquid crystalline thermosets (LCT's). LC epoxies are the monomers that have been most frequently studied to obtain LCT's. If the crosslinking is carried out in the mesophase, the LCTs obtained have unusual mechanical and thermal properties, low shrinkage upon cure, low thermal expansion coefficients, low dielectric constants and enhanced reaction rates because the ordered structures mean that the reacting groups are close to one another. Several publications describe the physical properties of oriented and unoriented LCT's. Macroscopically oriented LCTs obtained by curing in the mesomorphic state inside a magnetic field led to thermal expansion coefficient and storage modulus having anisotropic characteristics. Thus, the thermal expansion coefficient of macroscopically oriented materials must be lower than that of unoriented materials and the storage modulus must be expected to increase considerably in the direction of the orientation. I have synthesized six series of liquid-crystalline epoxy resins with aromatic azomethine groups and dimeric architecture, and varied the length of the alkyl spacer. The liquid crystal behaviour of these dimeric glycidylic compounds was studied by diferential scanning calorimetry (DSC), hot stage polarized optical microscopy (POM) and X-Ray Diffraction (WAXS). Two series of them show smectic mesophases and the other show nematic mesophase. From the results we have confirmed the importance of the polarization of the mesogenic groups and the presence of an ester group in the inner position in the formation of smectic mesophases.I obtained LCT's from these monomers by isothermal curing with equimolecular amounts of 2,4-diaminotoluene, 4,4'-amin