Sequential copolymerizations of trimethylene carbonate (TMC) and l-lactide (LLA) were performed with 2,2-dibutyl-2-stanna-1,3-oxepane as a bifunctional cyclic initiator. The block lengths were varied via the monomer/initiator and via the TMC/l-lactide ratio. The cyclic triblock copolymers were transformed in situ into multiblock copolymers by ring-opening polycondensation with sebacoyl chloride. The chemical compositions of the block copolymers were determined from (1)H NMR spectra. The formation of multiblock structures and the absence of transesterification were proven by (13)C NMR spectroscopy. Differential scanning calorimetry (DSC), wide-angle X-ray scattering (WAXS), and dynamic mechanical analysis (DMA) measurements confirmed the existence of a microphase-separated structure in the multiblock copolymers consisting of a crystalline phase of poly(LLA) blocks and an amorphous phase formed by the poly(TMC) blocks. Stress-strain measurements showed the elastomeric character of these biodegradable multiblock copolymers, particularly in copolymers having epsilon-caprolactone as comonomer in the poly(TMC) blocks.

Several polycondensations of ethylene carbonate with succinic anhydride or glutaric anhydride (GA) were conducted in bulk. Low molar mass polyesters were obtained with pyridine-type catalysts and GA. Analogous polycondensations of trimethylene carbonate (TMC) and GA were successful when quinoline, 4-(N,N'-dimethylamino)pyridine, or BF3 (.) OEt2 was used as a catalyst. Matrix-assisted laser desorption/ionization time-of-flight mass spectra revealed the formation of cyclic oligoesters and polyesters by backbiting degradation. Monomer mixtures containing an excess of TMC yielded copoly(ester carbonate)s with number-average molecular weights up to 16,000 Da. Analogous copoly(ester carbonate)s were obtained from TMC and 3,3'-tetramethylene glutaric anhydride. Furthermore, combined polycondensation/ring-opening polymerization reactions of TMC and GA with L-lactide or E-caprolactone were studied. All copolymers were characterized by viscosity measurements and by IR, H-1, and C-13 NMR spectroscopy. (C) 2002 Wiley Periodicals, Inc.

Ethylene sulfite and succinic anhydride undergo a polycondensation reaction evolving SO2 when heated above 160 degreesC in the presence of suitable catalysts. Both quinoline and Lewis acids (BF3 or SnCl4) proved to be useful catalysts yielding polyesters which were characterized by IR and H-1 and C-13 NMR spectroscopy. Analogous polycondensations were conducted with mixtures of ethylene sulfite and glutaric anhydride, 3,3-tetramethylene glutaric anhydride, adipic anhydride, and sebacic anhydride. The resulting polyesters had number average molecular weights (M(n)s) in the range of 5000-10 000 Da (based on PS-calibrated SEC), and the MALDI-TOF mass spectra indicated the formation of cyclic oligoesters and polyesters along with linear chains. Polycondensations of ethylene sulfite and succinyl sulfide yielded S-free polyesters, a result important for the mechanistic discussion. No polycondensations were observed for mixtures of ethylene sulfite and dicarboxylic acids, whereas oligoesters containing diethylene glycol units were obtained from acid-catalyzed polycondensations of ethylene glycol and cyclic anhydrides. The unusual thermodynamic aspects of this ring-opening polycondensation concept are also discussed.