The cationic ring-opening copolymerization behavior of SOC1 with BOXT and the properties of the obtained cross-linked copolymers are described. SOC1 and BOXT are cationally copolymerized under various feed ratios to obtain the corresponding cross-linked copolymers in 73-96% yields. The volume change during copolymerization could be controlled by the addition of SOC1 to obtain non-shrinking or volume-expanding copolymers. The glass transition temperatures (T-g) of the copolymers also decrease linearly with the feed ratio of SOC1, which suggests that the introduction of the flexible poly(SOC1) segment into the rigid BOXT cross-linked segment relieves the internal stress in the resins than severely degrade their mechanical properties.