Properties of liquid crystal epoxy thermosets cured in a magnetic field

Two liquid crystal diepoxides [1,4-phenylene bis(4-(2,3-epoxypropoxy)benzoa te) (A) and 4,4'-diglycidyloxydiphenyl (B)] were cured with a diamine [4,4' -diaminobiphenyl (C)] in the nematic phase to obtain liquid crystalline the rmoset (LCT) materials. The systems were studied using different curing con ditions and different ratios of the compounds. The mechanical properties we re investigated by stress/strain experiments to determine ultimate properti es (break strength and elongation at break) and dynamic mechanical thermal analysis (DMTA) to determine small strain properties as a function of tempe rature. An A/C mole ratio of 4/1 gave materials with the best combination o f high strength and percent elongation. The addition of a small amount of d iepoxide B to the system (with a mole ratio of A/B = 4/1) improves the mech anical properties. Dynamic mechanical thermal analysis shows that increasin g diamine content or curing time increases the cross-linking density. Macro scopic orientation of the LCTs was achieved by curing the mixtures in the p resence of a magnetic field. The samples show that the tensile modulus, bre ak strength, elongation at break, and the storage modulus below the glass t ransition all increase by a factor of about 2.