Fully imidized, high molecular weight polyimide homopolymers and random segmented poly(siloxane imide) and poly(aryl ether imide) copolymers were prepared for use as environmentally stable, tough structural matrix resins, structural adhesives, and dielectric materials. Although polyimides are well suited for such high performance engineering applications due to their excellent thermal and mechanical properties, their typical intractability in the fully imidized state has been a serious limitation. Therefore, this research has specifically focused upon several methods by which the processability of polyimide systems may be improved. One method involved the utilization of a solution imidization technique in converting the poly(amic acid) intermediate to the fully cyclized polyimide. Another important method was the incorporation of a monofunctional reagents to obtain controlled endgroups and molecular weights. Structural modifications achieved by either copolymerization with polydimethylsiloxane or polyaryl ether sulfones or ketones, or variation of the dianhydrides or diamines resulted in major strides in obtaining enhanced process ability, particularly when coupled with controlled molecular weight and the solution imidization technique. Significant reductions in the dielectric constant and water sorption, and improvements in processability were obtained by incorporating relatively nonpolar reactants, such as fluorinated dianhydrides, hydrophobic aromatic diamines, and polydimethylsiloxane oligomers. / Ph. D.