A sealant formulation consisting of Bu rubber plasticized with polyisobutylene and various amts. of brominated PhOH-CH2O resin was prepd. by using a twin screw corotating extruder at 200-300 rpm and filtered by using a 50 pm net. The formulations were extruded as a 1 mm thick tape. Its peel resistance at various temp. (23-70 degrees C) was evaluated. The melt vol. rate and peel adhesion of the formulations were detd. The partially crosslinked formulations showed an improved peel resistance and the acceptable processability as of uncured ones.