Equilibrium ring-opening polymerization theory has been extended to cycloolefin polymerizations. Previous work had established the reversible nature of the olefin metathesis reaction, the basic process whereby cycloolefins undergo ring-opening. The present work confirms the reversible character of cycloolefin polymerization for the cases of cyclopentene and bicyclo[4.3.0]nona-3.7-diene polymerization. Equilibrium conversion data for cyclopentene polymerizations have provided estimates of the enthalpy (-4.4 kcal/mole) and entropy (-14.9 cal/mole.deg) of polymerization. I n addition, some factors governing the polymerizability of mono-and multicyclic monomers are discussed. ZUSAMMENFASSUNG:Die Theorie der ringoffnenden Gleichgewichtspolymerisation wurde a d die Polymerisation von Cycloolefinen ausgedehnt. In friiheren Arbeiten wurde die reversible Natur der Olefin-Metathese aufgezeigt, der GrundprozeB, nach dem Cycloolefine einer Ringoffnung unterliegen. Die vorliegende Arbeit bestiitigt den reversiblen Charakter der Cycloolefinpolymerisation fur Cyclopenten und Bicyclo-[4.3.0]-nona-3.7-dien. Die Daten des Reaktionsgleichgewichts der Polymerisation von Cyclopenten lassen eine Abschitzung der Enthalpie der Polymerisation (-4,4 kcal/Mol) und der Polymerisationsentropie (-14,9 cal/ Mol. Grad) zu. AuBerdem werden einige Faktoren diskutiert, die die Polymerisierbarkeit von mono-und multicyclischen Monomeren beeinflussen.

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synopsisThe ring-opening polymerizations of cyclooctene, cyclododecene, 1,5cyclooctadiene, 1,5,9-~yclododecatriene, 3-methylcyclooctene, and 3-phenylcyclooctene have been carried out by using a twycomponent catalyst system composed of ethylaluminum dichloride and tungsten hexachloride. NMR and infrared analyses of the respective polymers indicate structures which are consistent with a ring-cleavage mode of propagation. No evidence for double-bond shifts or transannular reactions during the polymerizations of 1,5cyclooctadiene, 1,5,9-~yclododecatriene, 3-methylcyclooctene, and 3-phenylcyclooctene was found. The polymerizability of substituted, unsaturated, mediumsized alioyclic monomers suggests a convenient method for synthesis of certain perfectly alternating terpolymers. Since polymerizations occurred rapidly with little evolution of heat, it was concluded that entropy is a substantial contributor to the free energy of the ring-opening polymerization of medium-sized, unsaturated alicyclic monomers. 2209

In this paper views regarding the nature of the transition state in olefin metathesis are discussed. Earlier concepts that assumed a pairwise scrambling mechanism have been recently challenged. Metathesis studies involving acyclic as well as cyclic olefins have been reported which strongly suggest a chain process that may involve a carbene-to-metallocycle interconversion as the pathway responsible for transalkylidenation. Catalytic systems that display a low apparent metathesis activity on terminal olefins display a unique specificity in cross reactions with internal olefins. Critical experiments indicate that terminal olefins rapidly undergo regenerative metathesis preferentially. Results suggest that in the transient metallocycle, the most stringent steric requirements occur at the j3-carbon, although the origin of this steric demand is not obvious.

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