Polyethylene-like polyesters from w-hyroxyfatty acids

Our group developed a new family of biopolyesters that mimic polyethylene, are decorated with various functional groups (unsaturation, epoxy, hydroxyl) and are built from w-hydroxyfatty acids. Unlike polyethylene, the biopolyesters can be degraded by a mild enzymatic method. Thus, after biopolyesters function as a material, they can be degraded to high-value liquid fuels that are similar in structure and heat value to Soy Gold and other fatty acid ester biodiesels. For example, poly(w-pentadecalactone), PPDL, has: Young’s modulus 390±10 Mpa, elongation to break 58030 %, stress at break 58.8±3.1 MPa (corrected for change in thickness), stress at yield 21.4±0.4 MPa (corrected), and strain at yield 17.4±0.4 %. PPDL has properties intermediate to low and high density polyethylene showing excellent potential for use in applications where polyethylene currently is the material of choice. In collaboration with Prof. Scandola at the Univ. of Bologna (Italy), further investigations of poly(PDL) solid-state properties were performed by thermogravimetric analysis (TGA) coupled with mass spectrometry, differential scanning calorimetry (DSC), stress–strain measurements, wide-angle X-ray diffraction, dynamic mechanical and dielectric spectroscopies (Focarete et al., 2001). Poly(PDL) is a crystalline polymer that melts around 100 °C. The polyester shows good thermal stability, with a main TGA weight loss centered at 425 °C. Because of the high degree of poly(PDL) crystallinity, the glass transition (-27 °C) is revealed by relaxation techniques such as dynamic mechanical and dielectric spectroscopies, rather than by DSC. In addition to the glass transition, the viscoelastic spectrum of poly(PDL) also shows two low-temperature secondary relaxations centered at -130 (g) and -90 °C (b). They are attributed to local motions of the long methylene sequence (g) and complex units involving water associated with the ester groups (b). In agreement with the results above from tensile measurements, mechanical properties of poly(PDL) are typical of a hard, tough material, with a elastic modulus and yield parameters comparable to those of low-density polyethylene.