Two methylphenylsiloxane monomers with crosslinkable benzocyclobutene functionalities at the terminal positions, 1,1,5,5-dimethyldiphenyl-1,1,5,5-di[2'-(4'-benzocyclobutenyl)vinyl]-3,3-diphenyltrisiloxane (BCB-1) and 1,1,3,3-dimethyl-di-phenyl-1,1,3,3-di[2'-(4'-benzocyclobutenyl)vinyl]dis iloxane (BCB-2) were prepared and characterized. By heating the solution of BCB-1 and BCB-2 in mesitylene, two partially polymerized resins of BCB-1B and BCB-2B with high molecular weight were also achieved. The monomers and their oligomers fully cured at temperatures above 250 degrees C. Cured BCB-1 and BCB-2 exhibited high T-g (257 and 383 degrees C) and good thermal stability (T-5% > 472 degrees C both in N-2 and in air). They also demonstrated low dielectric constants (2.69 and 2.66), low dissipation factors (2.36 and 2.23), and low water absorptions (0.20% and 0.17%). Moreover, a negative photosensitive formulation derived from BCB-1B in combination with 2,6-bis(4-azidobenzylidene)-4-methylcyclohexanone (BAC-M) as a photosensitive agent has been developed. The photosensitive composition, BCB-1B containing 5 wt % BAC-M, showed a sensitivity of 550 mJ/cm(2) and a contrast of 1.96 when it was exposed to a 365 nm, light (i-line) and developed with cyclohexanone at 25 degrees C. A fine negative image of 10 mu m line-and-space pattern was also printed in a film which was exposed to 700 mJ/cm(2) of i-line by contact-printing mode. The negative image can be maintained without any pattern deformation in the curing process. (C) 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 6246-6258, 2009