Hydrocarbon resins were synthesized by thermal polymerization of the olefinic compounds of liquid pyrolysis products (the C(9+)fraction, heavy tar). The hydrocarbon resins were characterized by H-1 NMR spectroscopy, MALDI spectroscopy, and gel permeation chromatography. The effect of temperature, reaction time, feed composition, and solvent content on the yield, molecular weight, color, and molecular structure of the hydrocarbon resins was investigated. It was shown that addition of the C(9+)fraction to heavy tar increases the polymer yield while reducing the content of aromatic fragments in its structure.