Abstract: A method for the continuous manufacture of hydrocarbon resins starting from polymerizable insaturated hydrocarbons adapted to selectively obtain clear resins having well determined viscosities or softening points and to control the temperature of the polymerization reaction conducted in the presence of a Lewis acid as catalyst and recycling a fraction of the reaction mixture, due to the improvement comprising the steps of forming a close mixture of the catalyst and of the hydrocarbon fraction to be polymerized in a reactor, said mixture containing, by weight, from 0.05 to 0.8 part, and preferably from 0.1 to 0.

Abstract: A mixture of anhydrides homologous to tetra-hydrophthalic anhydride, having a melting point between 40.degree. and 50.degree.C. and comprising from 30 to 50 % of endo-methylene-tetrahydrophthalic anhydride, from 30 to 45 % of methyl-4-tetrahydrophthalic anhydride and from 10 to 25 % of methyl-3-tetrahydrophthalic anhydride and is obtained by the reaction in counter-flow of maleic anhydride with a petro-chemical C5 fraction, containing cyclopentadiene, isoprene and piperylene in substantially the same amount, together with other unsaturated C5 hydrocarbon fractions, selected from the group comprising the fractions derived from steam-cracking and pyrolysis of naphtha, the control of the conditions of temperature and flow-rate in order to have an essentially complete reaction, and the recovery of the resulting mixture of anhydrides.