Telomers of the formula <FORM:1016528/C3/1> in which Y and Z stand for the atoms or atomic groups formed by splitting a polychloroalkane with 2 to 3 carbon atoms and 5 to 8 chlorine atoms as telogen, and in which R1 to R4 stand for hydrogen or halogen atoms or organic substituents of molecular weight up to 300, and in which m and n are at least 1 and the sum of the average values of n and (n-1) is not less than 1 and not more than 50, and in which the order of the individual structural members in the chain is optional, are formed by reacting 1 mol of a polychloroalkane with 2 to 3 carbon atoms and 5 to 8 chlorine atoms with n mols of a diallyl phthalate, and in certain cases, also with (m - 1) mols of a monomer CR1R2=CR3R4, preferably in the presence of a catalyst supplying free radicals. When the monomer CR1R2=CR3R4 is used, R1 to R4 are as above and m and n are at least 1 so that the sum of n+(m-1) is not less than 1 and not more than 50. Preferred telogens are hexachloroethane, pentachloroethane and 1,1,1,2,-3,3,3-heptachloropropane and they may be used in the presence of other conventional telegens, lists of which are given. Lists of monomers CR1R2-CR3R4 and catalysts are given. In the examples o-diallyl-phthalate is telomerized and in one example the telomerized o-diallyl phthalate is mixed with a polyglycidylether resin, prepared by reacting epichlorohydrin with bis-(4-hydroxyphenyl)dimethylmethane in the presence of alkali, and t.-butylperbenzoate in dimethylphthalate and the mixture is used to impregnate glass fibre fabric.