Title

Liquid crystalline thermosetting polyimides

Date of Completion

January 1993

Keywords

Chemistry, Polymer

Degree

Ph.D.

Abstract

A binary system consisting of a chlorohydroquinone-based ester bismaleimide (3-Cl), T$\sb{\rm m}$ = 238$\sp\circ$C, and a methylhydroquinone-based ester bismaleimide (3-Me), T$\sb{\rm m}$ = 251$\sp\circ$C, was investigated for the purpose of improving processability by widening the nematic phase range before polymerization. Calculations based on the Schroeder-van Laar equation predicted a system eutectic composition of 41% 3-Me monomer and a eutectic temperature of 202$\sp\circ$C. Experiments found the eutectic composition at 35% 3-Me and the eutectic temperature at 218.5$\sp\circ$C. Discrepancies between experimental results and theoretical predictions are likely due to error in measured heats of fusion either due to impurities in the samples or due to the reactive nature of the components being considered. Thermal cycling was also found to have a significant melting point depression effect. While significant depression of the system melting point was achieved, polymerization still occurred immediately after melting in all systems evaluated. All mixtures could be polymerized from the nematic phase to yield a solid which retained the nematic orientation of the starting polymer melt.^ Amine-terminated and maleimide-terminated oligomers of molecular weight 1200-1800 based on 2,2$\sp\prime$-bis(trifluoromethyl)-4,4$\sp\prime $-diaminobiphenyl and 3,3$\sp\prime $4,4$\sp\prime$-biphenylenetetracarboxylic dianhydride were synthesized and characterized for lyotropic liquid crystalline behavior. Several different synthetic procedures were evaluated and a one-step procedure in m-cresol was found to be the most effective for producing fully imidized materials. Lyotropic behavior was observed only for the as-prepared solutions in m-cresol and in dilutions of this solution. Oligomer thermal stability was excellent, onsets of decomposition were in excess of 550$\sp\circ$C. Amine-terminated oligomers prepared in this way could be further reacted with cyanuric chloride or with bismaleimides to yield networks or network precursor materials. ^