Characterization of Thermal and Mechanical Properties of Hyperbranched Oligo(glycerol-glutaric acid)s

Dibutyltin oxide was used to catalyze the synthesis of oligo(glycerol-glutaric acid)s in the absence and presence of solvent. Reaction times were either 10 h or 24 h for reactions performed in DMF and 24 h for the neat reaction. The oligomers had an average yield of 84.6%. Gas chromatography (GC) was used to quantify amounts of unreacted glycerol and diacid. C-13 NMR was used to identify branching patterns and determine the degree of branching (DB%), MALDI-TOF mass spectrometry was used to detect ions that were unique to branched species, and gel permeation chromatography (GPC), equipped with a light scattering detector, was used to determine molecular weight (Mn) and the polydispersity index (PDI). Themal stability was determined by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA), while dynamic mechanical analysis (DMA) was used to determine the rheological properties of the products. The materials synthesized in solution had considerably lower average molecular weights (M-n, g/mol) of 1050 (10 h) and 1474 (24 h) but higher polydispersity indexes [PDI (M-w/M-n, where M-w = weight average molecular weight)] of 21.1 (10 h) and 30.5 (24 h), than the corresponding neat-derived material (M-n = 445,000; PDI = 5.8). Degrees of polymerization averaged 5.7 (10 h) and 8.8 (24 h) for the solvent-derived products compared to 2392.5 for products synthesized in the absence of solvent. Viscosity, glass transition temperature (T-g), change in heat capacity (Delta C-p), and molecular weight increased with reaction time and degrees of branching (DB%). Degrees of branching were lower for the solvent-derived materials [41% (10 h); 45% (24 h)] than observed for material synthesized in the absence of solvent (82%). DB% and M-n largely account for the drastic physical and mechanical differences observed among materials synthesized in solvent and solvent-less systems.