Kinetics of the Ring-Opening Polymerization of 6-, 7-, 9-, 12-, 13-, 16-, and 17-Membered Lactones. Comparison of Chemical and Enzymatic Polymerizations

The kinetics of bulk polymerization of 6-, 7-, 9-, 12-, 13-, 16-, and 17-membered lactones initiated with a zinc 2-ethylhexanoate/butyl alcohol system at 100 °C was studied and compared with that of lipase-catalyzed polymerization. Instantaneous concentrations of the lactone monomers were determined on the basis of the relative intensities of signals in the 1H NMR spectra (500 MHz, CDCl3 as a solvent, room temperature) from the ω-methylene protons (−(CH2)x-1CH2OC(O)−) (where x = 4, 5, 7, 10, 11, 14, and 15) in the lactone monomer and the polyester repeating units, respectively. Linearity of the semilogarithmic kinetic dependencies (ln([lactone]0/[lactone]) vs time), revealed a first order of propagation in monomer for all of the polymerizations studied. This kinetic behavior, pointing to the constant concentration of the involved active centers and thus to the practical elimination of termination side reaction, allowed the relative polymerization rates to be determined. The following order of polymerizati...