Copolymeric polythioesters by lipase-catalyzed thioesterification and transthioesterification of α,ω-alkanedithiols

Linear copolymeric polythioesters [PTE; poly(alpha,omega-alkanedioic acid-co-alpha,omega-alkanedithiols)] were formed in good yield (approximately 69%) by thioesterification of 1,12-dodecanedioic acid with 1,6-hexanedithiol and 1,8-octanedithiol, respectively, catalyzed by immobilized lipase from Rhizomucor miehei (Lipozyme RM IM) in vacuo without a solvent. Similarly, transthioesterification (thiolysis) of diethyl 1,12-dodecanedioate with 1,6-hexanedithiol led to the formation of approximately 66% PTE. Poly (1,12-dodecanedioic acid-co-1,6-hexanedithiol) and poly (1,12-dodecanedioic acid-co-1,8-octanedithiol) were extracted from the reaction mixture using methyl-t-butylether, precipitated at -20 degrees C and the precipitates extracted with boiling i-hexane to yield two fractions of PTE. The i-hexane-insoluble fraction of poly (1,12-dodecanedioic acid-co-1,6-hexanedithiol) shows an average molecular mass (Mw) of 1,212 Da, corresponding to a molecular weight range of up to 13,200 Da and a degree of polymerization of up to 38 monomer units. The i-hexane-insoluble fraction of poly (1,12-dodecanedioic acid-co-1,8-octanedithiol) shows a Mw of 2,360 Da, corresponding to a molecular weight range of up to 19,500 Da and a maximum degree of polymerization of up to 52 monomer units. The low-molecular weight (