a novel dicyanate ester of the formula : ## str1 ## wherein r 1 , r 2 , r 3 and r 4 are the same or different and each is hydrogen , alkyl , perfluoroalkyl , aryl or halogen ; a is a bridge selected from the group consisting of direct bond , methylene optionally mono - or di - substituted by alkyl , perfluoroalkyl and / or aryl , a five or six membered cycloalkylene , sulfonyl , thio , oxy , carbonyl , phenylene , and xylylene optionally substituted by alkyl at one or both methylene carbon atoms ; with the proviso that when the cyanato group is at the para - position relative to the bridge a , both r 1 and r 2 are not hydrogen , and its prepolymer are useful in the manufacture of electrical laminates having excellent dielectric properties in ghz region .