A Chemical Route to High Molecular Weight Vegetable Oil-Based Polyhydroxyalkanoate

To our knowledge, this is the first description of the material properties of a high molecular weight linear polyester prepared from the methyl ester of 9-hydoxynonanoic acid (HNME). The HNME of high purity was prepared by ozonolysis of castor oil, followed by methanolysis of triglycerides. High molecular weight polyester prepared in bulk by transesterification was a highly crystalline material with limited solubility in chlorinated solvents. The polyester is an analogue of polycaprolactone (PCL), but the longer hydrocarbon chain between ester groups imparted intermediate properties between polyesters and polyethylene, characterized by a higher melting point, higher T-g, better thermal stability, and lower solubility in chlorinated solvents than PCL. Differential scanning calorimetry showed only a single transition-melting at 70 degrees C with melting enthalpy of 95 J/g. Properties of the material were strongly dependent on the molecular weight. Lower molecular weight material was brittle with low mechanical strength and higher crystallinity and melting point while the high molecular weight polymer was spinnable into fibers of high toughness, strength, and elongation. Dynamic mechanical analysis at 10 Hz revealed a glass transition at -38 degrees C, and dielectric analysis revealed behavior similar to PCL. The polymer was stable up to about 250 degrees C as observed by thermogravimetric analysis.