Step-Growth Polyesters with Biobased (R)-1,3-Butanediol

We present the synthesis and characterization of polymers containing 1,3-butanediol, also known as butylene glycol. Butylene glycol (BG) can be prepared from petroleum or sugar-based feedstocks. Petrolbased BG (petrol-BG) is isolated as a racemic mixture, whereas the biobased BG from sugar that we utilized (bio-BG) is enantiopure upon OH purification (>99.7%). In the presence of a titanium catalyst, polyesters were prepared by transesterification polymerization between petrol- or bio-BG and various aliphatic and aromatic diacid derivatives. Polymers were analyzed by size-exclusion chromatography (SEC), H-1 NMR and C-13 NMR spectroscopies, thermogravimetric analysis (TGA), and differential scanning calorimetry (DSC). The synthesized polyesters were statistical in nature, according to C-13 NMR spectroscopy, a result of the asymmetric nature of the BG-starting material. As a result, many of the polyesters were amorphous in nature with low thermal glass transitions (T-g) and no melting points (T-m). In many of the polyester derivatives, the racemic petrol-based and enantiopure biobased BG polymers were nearly identical in thermal performance. Differences arose in semicrystalline polyesters with long, aliphatic backbones (e.g., 1,14-tetradecanediocic acid; C14 diacid) or regioregular 4-hydroxybenzoate polyesters. This suggests the polymer microstructure (statistical versus sequenced) and the optical activity (racemic versus enantiopure) are important determinates in establishing the structure-property relationships in BG-containing polyesters. This work establishes synthetic protocols and the foundation for materials based on BG-containing polymers.