Abstract: Sulphur product, (P), process for making (P), films, molded articles made therefrom, wherein (P) is obtained by the addition reaction of at least one polythiol (I) with at least one compound of formula (II): in which R1 represents a linear or branched aliphatic residue comprising an ethylenic unsaturation double bond, it being optional for the latter to be that by which R1 is connected to the norbornene ring, it also being optional for the said ring to comprise other substituents chosen from C1-C3 alkyl groups, in proportions corresponding or substantially corresponding to one thiol group of the polythiol or polythiols (I) per mole of the compound or compounds (II), the thiol groups of the compound or compounds (I) adding predominantly to the cyclic double bond of the compound or compounds (II) and, on average, one ethylenic unsaturation of a compound (II) of the two which it carries remaining free; or sulphur product, (P′), obtained by the addition reaction of at least one polythiol (