Resins prepared by the catalytic reaction of p-alltylphenols with acetylene in the presence of an inert diluent at elevated temperature and pressure, and obtained in the molecular weight range of 800 to 1100, are brittle solids resembling, in some respects, the oil-soluble alkylphenolaldehyde condensation products. Thep-tert-butylphenolacetylene resin, known as Koresin, developed first in Germany and now made in this country is one of the most effective tackifiers for Buna S and GR-S known. In addition to duplicating the foreign-made material, several reaction variables were studied.Also, p-tert-amylphenol and diisobutylphenol were made to react with acetylene to form products similar to Koresin, but of somewhat lower tack values and melting points. The physical prop-erties studied included solubility, compatibility, cloud point, melting point, molecular weight, stability, infrared absorption spectra, and x-ray pattern. Observations on the methods of application to synthetic rubbers and other possible uses are given. A discussion of the reaction mechanism and polymer structure is included and the following formula is proposed: RESINS prepared by the catalytic reaction of p-alkylphenols with acetylene in the presence of an inert diluent at elevated temperature and pressure (28, 24), and obtained in the molecular weight range of 800 to 1100, are brittle solids resembling, in some respects, the oil-soluble alkylphenol-aldehyde con-