MODELING RING-CHAIN EQUILIBRIA IN RING-OPENING POLYMERIZATION OF CYCLOOLEFINS

A combined computational and theoretical method is developed to predic t the equilibrium ring-chain distribution of the products of ring-open ing metathesis polymerization (ROMP). In ring-chain equilibria, the fr ee energy change of the reaction includes an entropic cost associated with forming cyclic rather than linear products and an enthalpic cost if ring strain is significant (i.e., for small rings); The entropy cha nge is determined using statistical mechanics (based on the Jacobson-S tockmayer theory). The enthalpy change is computed with a Monte Carlo configurational search using molecular mechanics (MM3). Using the resu lting equilibrium constants, the calculated distribution of cyclic and linear products is in good agreement with experiment. To characterize the polymerizability of cycloolefins, we compute the critical concent ration [M](c,infinity), defined as the total monomer lost to cyclic pr oducts.