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- Polycondensation (2) (entfernen)
Numerous polycondensations of isosorbide and suberoyl chloride or other aliphatic dicarboxylic acid dichlorides were performed with pyridine as a catalyst and HCl acceptor. The reaction conditions were varied to optimize both the molecular weight and the fraction of cyclic oligo- and polyesters. Furthermore, we attempted to obtain the cyclic monomer by catalyzed back-biting degradation of the molten cyclic polyesters above 220 °C in vacuo. The polyesters were characterized by viscosity and size exclusion chromatographic measurements as well as matrix-assisted laser desorption/ionization time-of-flight mass spectrometry. In selected cases, mixtures of linear and cyclic polyesters were treated with a hot solution of partially methylated ß-cyclodextrin in methanol. This treatment allowed for a selective extraction of the linear chains up to approximately 5000 Da.
Isosorbide, succinyl chloride and isophthaloyl chloride are polycondensed under various reaction conditions. The heating in bulk with or without catalysts as well in an aromatic solvent without catalyst, and polycondensation with the addition of pyridine only yield low molar mass copolyesters. However, heating in chlorobenzene with addition of SnCl2 or ZnCl2 produces satisfactory molar masses. The number average molecular weights (Mn) of most copolyesters fall into the range of 7000–15,000 Da with polydispersities (PD) in the range of 3–9. The MALDI-TOF mass spectra almost exclusively displayed peaks of cyclics indicating that the chain growth was mainly limited by cyclization and not by side reactions, stoichiometric imbalance or incomplete conversion. The glass-transition temperatures increased with the content of isophthalic acid from 75 to 180 °C and the thermo-stabilities also followed this trend.