Benzocyclobutenes: A New Class of High Performance Polymers

Benzocyclobutenes are a family of thermally polymerizable monomers which can be classified into two groups: 1) monomers which contain only benzocyclobutene moieties and 2) monomers which contain sites of unsaturation in addition to benzocyclobutene moieties. The monomers can be partially polymerized (B-staged) by heating to form oligomers having processing advantages for various composite fabrication techniques. The polymerization proceeds through the thermally initiated cyclobutene ring opening to yield an o-quinodimethane intermediate (calculated to be a ground state singlet). Preliminary characterization of the network structures indicates that monomers which contained multiple benzocyclobutene moieties, optionally with sites of unsaturation, were transformed into multifunctional network junctions when the thermosets were fully cured. The 3-maleimidobenzocyclobutenes thermally polymerize to yield substantially linear, high glass transition temperature (T_g) polymers. Thus benzocyclobutene polymers encompass materials which have properties ranging from high T_g, thermosets to those of substantially linear thermoplastics. Some polymers exhibit an excellent retention of their room temperature mechanical properties to at least 200-250°C, making them useful as high performance polymers for applications in the aerospace industry. Other polymers have outstanding electrical properties including very low dielectric constant and water pickup, making them useful in electronic applications.