Syntheses of Aliphatic Polyesters Catalyzed by Lanthanide Triflates MAZEN GARALEH, 1,2 MOHAMMED LAHCINI, 1,3 HANS R. KRICHELDORF, 1 STEFFEN M. WEIDNER 4 1 Institut fu ¨ r Technische und Makromolekulare Chemie, Bundesstr. 45, D-20146 Hamburg, Germany 2 Dept. of Applied Chemistry, Tafila Techn. Univ., Tafila, Jordan 3 Univ. Cadi Ayyad, Dept. de Chimie, LCBM, BP 549, Marrakech, Maroc 4 Bundesanstalt fu ¨ r Materialforschung u.-pru ¨ fung (BAM), Fed. Inst. Mater. Research & Testing, 1.35 ‘‘Polymer Analysis’’, Richard-Willsta ¨tter-Str. 11, D-12489 Berlin, Germany Received 8 October 2008; accepted 9 October 2008 DOI: 10.1002/pola.23136 Published online in Wiley InterScience (www.interscience.wiley.com). ABSTRACT: Polycondensations of 1,6-hexane diol and sebacic acid were conducted in bulk with addition of a lanthanide triflate as acidic catalyst. With exception of prome- thium triflate all lanthanide triflates were studied. A particularly low molecular weight was obtained with neodym triflate and the best results with samarium triflate. With Sm(OTf) 3 weight average (M w ) values up to 65 kDa (uncorrected SEC data) were achieved after optimization of the reaction conditions. Comparison of these results with those obtained from bismuth, magnesium, and zinc triflates, on the one hand, and com- parison with the acidities of all catalysts, on the other, indicates that the esterification mechanism involves complexation of monomer by metal ions. Preparation of multiblock copoly(ether ester)s failed due to insufficient incorporation of poly(tetrahydrofuran) diols. V V C 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 170–177, 2009 Keywords: biodegradable polyesters; lanthanide ions; macrocycles; MALDI-TOF; polycondensation INTRODUCTION Over the past 20 years aliphatic polyesters have attracted much interest as biodegradable materi- als. Two quite different synthetic strategies were explored in much detail, firstly, ring-opening poly- merization of lactanes and other cyclic esters and, secondly, polycondensation of a,x-alkane diols with aliphatic dicarboxylic acids (ADAs). The present work is part of broader study of the sec- ond synthetic strategy. The classical approach to syntheses of polyest- ers from aliphatic diols by polycondensation with ADAs in bulk at temperatures up to 250  C was elaborated by Carothers. 1,2 This approach usually yields low number average molecular weights (M n s in the range of 2000–4000 Da). Only in few cases heating in vacuo for a long time (e.g., 12 days) yielded M n s up to 12,000 Da. 2 This approach is inconvenient and comes into conflict with the moderate thermostability of aliphatic polyesters. 3 Lower reaction temperatures (180– 200  C) and higher molecular weights were reported for polysuccinates, when distannoxanes were added as transesterification catalysts. 4 Yet, commercial poly(butylenes succinate) having M n s above 10,000 Da is chain extended with Correspondence to: H. R. Kricheldorf (E-mail: kricheld@ chemie.uni-hamburg.de). Journal of Polymer Science: Part A: Polymer Chemistry, Vol. 47, 170–177 (2009) V C 2008 Wiley Periodicals, Inc. 170