Partially aliphatic, high molecular weight polyimide copolymers were successfully synthesized using an ester−acid high-temperature solution imidization route by which noncrystalline, soluble materials were obtained. Variations in the aliphatic content produced a series of polyimides having different glass transition temperatures and processing characteristics. The ester−acid reaction pathway eliminated the need for anhydrous solvents and overcame the problem of salt formation commonly observed for nucleophilic, more basic, aliphatic amines prepared by the traditional poly(amic acid) synthesis route. Partially aliphatic polyimides containing either a cycloaliphatic diamine or aliphatic diamines with 6 or 12 methylene units were synthesized. Each copolymer was characterized by its molecular weight, glass transition temperature, thermal stability, coefficient of thermal expansion, refractive index, and dielectric constant. Structure−property relationships were established. The γ and β sub-T g viscoelastic relaxations were explored in order to understand their molecular origins.

High molecular weight, soluble, amorphous, partially aliphatic polyimides were successfully synthesized using an ester acid high‐temperature solution imidization route, which allows one to control desired glass‐transition (Tg) and processing temperatures. This method involves the prereaction of aromatic dianhydrides with ethanol and a tertiary amine catalyst to form ester acids, followed by the addition of diamines. Subsequent thermal reaction forms fully cyclized polyimides. This reaction pathway eliminates the need for anhydrous solvents and overcomes the problem of salt formation commonly observed for nucleophilic, more‐basic aliphatic amines when utilizing the traditional polyamic acid synthesis route. The molar ratio of aromatic‐to‐aliphatic diamines was varied to generate a series of copolyimides with the chosen dianhydride and tailor the physical properties for specific adhesive applications. This series of copolyimides was characterized by their molecular weight, Tg, thermal stability, coefficient of thermal expansion, refractive index, and dielectric constant. Structure‐property relationships were established. The γ and β sub‐Tg viscoelastic properties were researched to understand their molecular origins. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 1503–1512, 2002