Ring-opening polymerization of diisopropyl cyclopropane-1,1-dicarboxylate under living anionic conditions: A kinetic and mechanistic study

Diisopropyl cyclopropane-1,1-dicarboxylate (1) undergoes ring-opening polym erization in the presence of thiophenolate anions acting as initiator. A ca rbon-chain polymer, substituted on every third carbon atom by two isopropyl ester substituents, is obtained, whose structure and molecular weight were characterized by several analytical techniques. Under typical reaction con ditions, only the expected ring-opened structure with a phenylthio end grou p is obtained, with no evidence for side reactions during the initiation an d propagation steps. A kinetic study of the polymerization, at 140 degrees C in the presence of sodium thiophenolate, showed that the degree of polyme rization increases linearly with conversion. The final polymers have narrow molecular weight distributions ((M) over bar(w)/(M) over bar(n) < 1.13), a nd the reaction follows a first-order kinetics with respect to the monomer over the entire conversion range. These results support a living mechanism for the polymerization. The nature of the counterion and the presence of co unterion complexing agents, like crown ether and cryptand, significantly in crease the reaction rate. A linear Arrhenius behavior was found in the 130- 190 degrees C range, with an activation energy of 21.3 kcal mol(-1). At hig her temperatures deviation from the linear Arrhenius behavior and appearanc e of new peaks in H-1 NMR can be observed. Thermogravimetric analysis shows that the polymer is thermally stable up to 270 degrees C. Poly(1) is highl y crystalline, with a melting point in the 168-76 degrees C range.