An improved method for the diimide hydrogenation of butadiene and isoprene containing polymers

Abstract

The hydrogenation of unsaturated polymers with diimide generated in‐situ by thermolysis of p‐toluenesulfonyl hydrazide (TSH) is a commonly used method for preparing laboratory scale quantities of saturated diene based polymers. The by‐products from TSH, particularly p‐toluenesulfinic acid, can attack at olefinic sites, adding p‐tolylsulfone functionality and degrading polymer molecular weight. The addition of tri‐n‐propyl amine has been found to eliminate these side reactions in butadiene containing polymers and copolymers, enabling the preparation of polymers devoid of backbone unsaturation. No detectable sulfur‐containing impurities were indicated by IR, NMR, or elemental analysis, and no chain degradation was observed via GPC analysis of the hydrogenated polymers. cis‐Polybutadiene and butadiene containing random and block copolymers with styrene were hydrogenated cleanly using this technique. A ratio of 2 mol TSH and 2 mol amine/mol of olefin was necessary to assure > 99% hydrogenation, and a w/v ratio of 2 parts butadiene/100 parts o‐xylene gave the most efficient hydrogenation. Polymers prepared from isoprene were only partially hydrogenated when treated with TSH in the presence of tri‐n‐propyl amine, and gave evidence of slight degradation of the polymer structure.