Ring-Opening Metathesis Polymerization of a Naturally Derived Macrocyclic Glycolipid PengYifeng DecaturJohn A. R. MeierMichael GrossRichard A. 2013 Lactonic sophorolipid (LSL) is a naturally occurring macrocyclic monomer that undergoes ring-opening metathesis polymerization (ROMP) via an entropy-driven mechanism (ED-ROMP). Typically, gel permeation chromatographic analysis of poly­(LSL) showed products consist of about 70% polymer with <i>M</i><sub>n</sub> up to about 180K (<i>M</i><sub>w</sub>/<i>M</i><sub>n</sub> 1.6–1.8) coexisting with 10% of oligomer and 20% monomer. Detailed kinetic studies for LSL ROMP were performed using two classic metathesis catalysts (i.e., G2 and G3). G2 exhibited apparent first-order propagation, although its slow initiation caused subsequent events of secondary metathesis that decreased molecular weight. An induction period observed for G2 at 33 and 45 °C largely disappears at 60 °C with an increase in the apparent rate constant (<i>k</i><sub>p</sub><sup>app</sup>) of 11 times. G3 gave fast initiation even at 33 °C while plots of ln­{[M]<sub>0</sub>/[M]<sub><i>t</i></sub>} versus reaction time for G3 show that <i>k</i><sub>p</sub> continuously decreased, implying a decline in G3 catalytic activity. Plots of ln­{[M]<sub>0</sub>/[M]<sub><i>t</i></sub>} versus reaction time for G2 are linear, suggesting apparent first-order kinetic behavior. From analysis of an Arrhenius plot for G2-catalyzed LSL polymerization in THF, the activation energy (<i>E</i><sub>a</sub>) of propagation is 18 ± 3 kcal/mol. By keeping [LSL] constant at 0.54 M, G2-catalyzed LSL ED-ROMP (60 °C, THF) gave a plot of <i>M</i><sub>n</sub> versus [monomer]/[initiator] ratio close to that of the theoretical curve based on a living polymerization model. Hence, despite pronounced secondary metathesis in ED-ROMP, polymerization kinetics with G2 closely resembled living behavior. The length of the induction period for G2-catalyzed polymerizations is inversely proportional to the solvent dielectric constant (ε<sub>DCM</sub> > ε<sub>THF</sub> > ε<sub>CHCl<sub>3</sub></sub>). Finally, this work provides an important example of how complex structures derived from nature can be transformed into unique macromolecules.