Synthesis and characterization of photosensitive benzocyclobutene-functionalized siloxane thermosets

Zuo, Xiaobiao; Yu, Ruilian; Xi, Song; Feng, Zhihai; Li, Zhongping; Yang, Shiyong; Fan, Lin

Synthesis and characterization of photosensitive benzocyclobutene-functionalized siloxane thermosets

2009

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-diphenyl-1,1,3,3-di[2'-(4'-benzocyclobutenyl)vinyl]disiloxane (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 °C. Cured BCB-1 and BCB-2 exhibited high Tg (257 and 383 °C) and good thermal stability (T₅% > 472 °C both in N₂ 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/cm² and a contrast of 1.96 when it was exposed to a 365 nm light (i-line) and developed with cyclohexanone at 25 °C. A fine negative image of 10 μm line-and-space pattern was also printed in a film which was exposed to 700 mJ/cm² of i-line by contact-printing mode. The negative image can be maintained without any pattern deformation in the curing process.

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