Study of benzocyclobutene-functionalized siloxane thermoset with a cyclic structure

In this paper, a new kind of benzocyclobutene-functionalized siloxane monomer, 1,3,5,7,-tetramethyl-1,3,5,7-tetra[2´-(4´-benzocyclobutenyl)]vinylcyclotetra-siloxane (CYC-BCB), is synthesized and characterized. For comparison, the commercialized resin, 1,1,3,3-tetramethyl-1,3-bis [2´-(4´-benzocyclobutenyl)]vinyldisiloxane (DVS-BCB) is also prepared. Partially polymerized resins, P-DVS-BCB, P-CYC-BCB, are obtained by refluxing the mesitylene solution of those corresponding monomers. The chemical structure of these monomers and their partially or fully polymerized resins are characterized by FTIR. All these monomers and their partially polymerized resins show similar curing behavior with an exothermal maximum at nearly 260°C. The cured CYC-BCB resin exhibit a better thermal stability, higher glass transition temperature (T_g) and higher storage modulus in comparison with the DVS-BCB resin. Moreover, cured CYC-BCB resins also demonstrate low dielectric constants (<; 2.8 at f=1 MHz) and low water absorptions (<; 0.8% after submersion in boiling water for 5 days). The cured films prepared from the mesitylene solution of P-CYC-BCB show a well planarization (maximum height difference <; 4nm).