Ring-chain equilibrium polymer molecular distribution

Figure I. Typical molecular distribution for a ring-chain equilibrium polymer...

Presently available information is insufficient to permit deciding whether the high molecular weight polymers obtained in ordinary polymerizations of cycloolefins consist of macrocyclics alone or mixtures of rings and chains. Nevertheless, the intentional introduction of known amounts of chain ends via addition of vinylenic olefins should result in ring-chain equilibrium of the type presented in Reaction 11. For this type of equilibrium, the weight fractions and size distributions of rings and chains present in the system may be compared with the Jacobson and Stockmayer theory (8). Experiments to test theory in this area are currently underway. 

There is, of course, an equilibrium between the monomers and polymer in the lipase-catalyzed polycondensation of dialkyl esters and glycols. In the lipase CC- or MM-catalyzed polymerization of dimethyl succinate and 1,6-hexanediol in toluene, adsorption of methanol by molecular sieves or elimination of methanol by nitrogen bubbling shifted the thermodynamic equilibrium (101). When dicar-boxy lie acid dialkyl esters and a , >-alkylene glycols were used as monomers, cyclic oligomers were formed from any monomer combinations examined (102). The yield of the cyclics depended on the monomer structure, initial concentration of the monomers, and reaction temperature. The ring-chain equilibrium was observed and the molar distribution of the cyclic species obeyed the Jacobson-Stockmayer equation. 

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