Lipase-Catalyzed Polycondensations: Effect of Substrates and Solvent on Chain Formation, Dispersity, and End-Group Structure

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Abstract
The effects of substrates and solvent on polymer formation, number-average molecular weight (Mn), polydispersity, and end-group structure for lipase-catalyzed polycondensations were investigated. Diphenyl ether was found to be the preferred solvent for the polyesterification of adipic acid and 1,8-octanediol giving a Mnof 28 500 (48 h, 70 °C). The effect of varying the alkylene chain length of diols and diacids on the molecular weight distribution and the polymer end-group structure was assessed. A series of diacids (succinic, glutaric, adipic, and sebacic acid) and diols (1,4-butanediol, 1,6-hexanediol, and 1,8-octanediol) were polymerized in solution and in bulk. It was found that reactions involving monomers having longer alkylene chain lengths of diacids (sebacic and adipic acid) and diols (1,8-octanediol and 1,6-hexanediol) give a higher reactivity than reactions of shorter chain-length diacids (succinic and glutaric acid) and 1,4-butanediol. The bulk lipase-catalyzed condensation reactions were feasible, but the use of diphenyl ether gave higher Mn values (42 400 g/mol in 3 days at 70 °C). The polydispersity varied little over the conditions studied giving values ≤2. No specific trend with respect to end-group structure as a function of time was observed. At 70 °C, the retention of catalyst activity in the bulk was independent of substrate structure but was higher when reactions were conducted in diphenyl ether than in bulk.