Physical characterization of poly(w-pentadecalactone) synthesized by lipase-catalyzed ring-opening polymerization

The Candida antarctica lipase B (Novozyme-435)-catalyzed ring-opening polymn. of w-pentadecalactone in toluene was performed. Poly(w-pentadecalactone) [poly(PDL)] was obtained in a 93% isolated yield in 4 h with a no.-av. mol. wt. of 64.5 ´ 103 g/mol and a polydispersity index of 2.0. The solid-state properties of poly(PDL) were investigated by thermogravimetric anal. (TGA) coupled with mass spectrometry, differential scanning calorimetry (DSC), stress-strain measurements, wide-angle x-ray diffraction, and dynamic mech. and dielec. spectroscopies. Poly(PDL) is a cryst. polymer that melts around 100°. The polyester shows good thermal stability, with a main TGA wt. loss centered at 425°. Because of the high degree of poly(PDL) crystallinity, the glass transition (-27°) is revealed by relaxation techniques such as dynamic mech. and dielec. spectroscopies, rather than by DSC. In addn. to the glass transition, the viscoelastic spectrum of poly(PDL) also shows 2 low-temp. secondary relaxations centered at -130 (g) and -90° (b). They are attributed to local motions of the long methylene sequence (g) and complex units involving water assocd. with the ester groups (b). The mech. properties of poly(PDL) are typical of a hard, tough material, with an elastic modulus and yield parameters comparable to those of low-d. polyethylene.