Preparation and characterization of liquid crystalline polyurethane‐imide modified epoxy resin composites

Liquid crystalline polyurethane‐imide (PUI) was synthesized from polyethyleneglycol, toluene diisocyarate, and pyromellitic dianhydride by solution polymerization and characterized by FTIR spectrum. The liquid crystal properties of PUI were verified by differential scanning calorimetry, polarizing microscope (POM), and X‐ray diffraction. PUI is a longitudinal liquid crystal with LC sequences in the backbone along the main‐chain direction. PUI was used to blend with epoxy resin(ER) as a modifier. The mechanical properties, thermal property, and morphology of PUI/ER composites were investigated. It was found that PUI was a kind of thermotropic liquid crystal material within a wide range of temperature. Remarkable improvement in strength and toughness of ER/PUI composites was achieved by the blending of PUI with epoxy in appropriate proportions. The maximum for bending strain and bending strength of the composite reached the level of 10.65% and 178 MPa, respectively when the mass fraction of PUI was 15 wt%. The mechanical behaviors of the PUI/ER were consistent with morphology analysis of the fracture surfaces of PUI/ER composites from SEM. POLYM. ENG. SCI., 54:1704–1711, 2014. © 2013 Society of Plastics Engineers