Benzocyclobutene in polymer synthesis. I. Homopolymerization of bisbenzocyclobutene aromatic imides to form high‐temperature resistant thermosetting resins

A series of new bisbenzocyclobutene‐terminated aromatic imide monomers has been synthesized from the condensation reaction of 4‐aminobenzocyclobutene and the perspective dianhydride in refluxing acetic acid/toluene. The differential scanning calorimetric studies of the foregoing monomers indicated that polymerization exotherms began at 229–250°C and reached their maxima at 258–263°C. The cured samples (250–254°C; N 2 ; 8 h) were surprisingly stable toward thermo‐oxidative degradation; only 7–10% weight loss was observed after 200 h (in air) at 314°C (600°F). At higher temperatures (650 and 700°F), the most rigid structure was the most thermo‐oxidatively stable. An approach to enhance both the final glass‐transition temperature ( T g cure) and the thermo‐oxidative stability of the bisbenzocyclobutene system was to dilute the cure‐site density since the cure‐site structure is the weakest part of the polymeric structure. Therefore, a series of bisbenzocyclobutene‐terminated aromatic imide oligomers were prepared, using various aromatic amines as the chain‐extending agents. Meta ‐phenylenediamine was apparently the most effective in the advancement of both the T g (cure) and thermo‐oxidative stability.