Hydrogenation of low molar mass OH‐telechelic polybutadienes catalyzed by homogeneous Ziegler nickel catalysts

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Abstract

Abstract Two types of low molar mass, medium vinylic polybutadienes containing 2‐hydroxypropyl and 2‐hydroxyethyl end groups were hydrogenated in the presence of several homogeneous Ziegler Ni catalysts prepared by using Ni(acac) 2 and Ni(2‐ethylhexanoate) 2 as metal precursors and BuLi, Li adduct to a diene and Et 3 Al as activators. The catalytic efficiency of these systems determined by rate measurements showed that the best results can be achieved with the Ni(2‐hexanoate) 2 + Li‐diene (Ni : Li mol ratio = l : 8–10) catalyst in the solvents commonly used in the synthesis of these polyalkadienes by anionic polymerization of 1,3‐butadiene. As found by the kinetic study, the hydrogenation carried out under mild reaction conditions (temperatures of 10–35°C, hydrogen pressure of 72–178 kPa, Ni concentration of 2.1–10.0 mmol/dm −3 ) was the first order in the OH‐polybutadiene and hydrogen and, over narrow range of catalyst concentrations (4.3–10.0 mmol Ni/dm −3 ), also in the catalyst. The activation energy of the hydrogenation estimated from the Arrhenius plot was 42 kJ/mol. Changes in the relative proportion of 1,2‐, cis ‐1,4‐, and trans ‐1,4‐CC units of the polymer during hydrogenation indicate the selectivity of the catalyst to the 1,2‐hydrogenation. The ease of the addition of hydrogen to the internal CC unsaturation was found to be opposite to that usually observed ( trans > cis ). The present low‐pressure hydrogenation of both types of telechelic OH‐polybutadienes proceeds with full retention of the average OH functionality and affords the saturated polymers, the residual CC unsaturation of which (<1%) has so far been usually achieved by high‐pressure hydrogenations. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 1185–1193, 2002

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