Aliphatic polyesters based on 1,4-butanediol and even numbered C4 - C20 dicarboxylic acids - synthesis and properties including after surface treatment by VUV photo-oxidation

Aliphatic polyesters were synthesized from 1,4-butanediol and predominantly renewable dicarboxylic acids containing even numbered carbons from 4 to 20 (succinic acid to eicosanedioic acid). Melt polymerizations were conducted up to 220 °C with titanium tetrabutoxide as polymerization catalyst. Two polymerization methods were applied: (1) stoichiometrically equivalent amounts of diol and diacid with 14 hours under argon followed by 10 hours under reduced pressure, (2) a 10 mol % excess of diol, with 6 hours under the inert gas and 6 hours under reduced pressure. Molecular weight properties were determined by size exclusion chromatography in chloroform and polystyrene as calibration standards. For the polyesters with the C6 to C20 diacids, M_w obtained by Method 1 lied between 15,800 to 31,200 g/mol, and for Method 2 between 27,000 and 180,400 g/mol (average of M_w for PBS was 194,000 g/mol). ¹H NMR and ¹³C NMR spectra of all polymers were obtained, peak assignments were made and the microstructure of the polymers was verified. In addition, peaks associated with end-groups were identified. Thermal properties of the polymers were determined by differential scanning calorimetry, dynamic mechanical analysis and thermal gravimetric analysis. For the polyesters obtained with C6 to C20 diacids, the highest T_g was 1.25 °C (from tan δ) and the highest T_m was 88.8 °C, both with the C20 diacid. The polymers were also treated by vacuum ultraviolet (VUV) photo-oxidation as a plasma surface modification. The wettability of the original polymers and after their VUV photo-oxidation was measured by contact angle goniometry with water.