Molecular distribution, ring-chain

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. 

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

Involves ring-chain equilibria and In order to produce at least 90 percent of the chain composition the polymerization temperature Is typically about 0°C or lower. The polymerization Is often analogous to a living system, at least In the sense that the molecular weight Increases linearly with conversion and that relatively narrow molecular weight distributions can be achieved. The nature of the counter Ion can be Important and side reactions such as halogen chain transfer have been Identified. Such a process would destroy the functionality and appears to Increase as the counter Ion Is varied In the order shown ... 

Specific sources on molecular mass distributions are Plory PJ (1953) Principles of Polymer Chemistry, Chaps 3, 8 and 9. Cornell University Press, Ithaca Peebles LH (1971) Molecular Weight Distributions in Polymers. Wiley-Interscience, New York The problem of ring formation is treated by Jacobson H, Stockmeyer WH (1950) Intramolecular Reaction in Polycondensation. I. The Theory of Linear Systems. J Chem Phys 18 1600-1606 and Jacobson H, Beckmann CO, Stockmeyer WH (1950), II. Ring-chain Equilibria in Polydeca-methylene Adipate. J Chem Phys 18 1607-1612. 

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. 

C — molecular size distribution of chains R — molecular size distribution of rings... 

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