"The overall goal of this work was to develop new polyimide systems for aerospace and optical applications. The work was divided into two parts. The first included the synthesis and characterization of low melt viscosity imide oligomers, and the second included the synthesis and characterization of polyimides with twisted configurations. The objective of the first part was to develop phenylethynyl-terminated imide oligomers for use in resin transfer molding (RTM) or resin infusion (RIF) composite fabrication. Some A-B monomer precursors, which possessed both nitro and anhydride functionalities, were synthesized for use in preparation of well-defined oligometers. Thus, a series of star-shaped oligomers and a series of linear oligomers containing twisted-biphenyl structures were prepared from different diamines and dianhydrides and then end-capped with 4-phenylethynylphthalic anhydride (PEPA). Most of the star-shaped oligomers displayed either high melt viscosities or high Tgs and Tms. However, one oligomer which was prepared from 1,3,5-tris(3-aminophenoxy)benzene displayed a low melt viscosity of 1 poise at 260°C and could be thermally cured to resin with a Tg above 350°C. Some of the linear twisted oligomers, which were prepared from 2,2'-bis(o-aminophenoxy)biphenyl, also displayed very low melt viscosities that ranged from 0.5 to 15 poise at 280°C. These materials could be thermally cured to resins with Tgs near 300°C. Oligomer blends were also prepared by solution mixing. Some of blends also displayed very low melt viscosities that ranged from 2 to 10 poise at 280°C. The blends could be thermally cured to resins with Tgs above 300°C. The objective of the second part of this work was to develop polyimides for use in optical applications that require non-biregringent materials. Thus, four series of polymers were prepared from 2,2'-bis(m-aminophenoxy)biphenyl, 2,2'-bis(o-aminophenoxy)biphenyl, 2,2'-bis(2-amino-4-trifluoromethylphenoxy)biphenyl and 2,2'-bis(2,3-dicarboxyphenoxy)biphenyl dianhydride. The polymers containing twisted biphenyl structures were soluble in common organic solvents and could be solution cast into clear, transparent flexible films 10-15 [mu]m thick. The films displayed birefringences ranging from 0.0257 to 0.0021"--Abstract