Macrocyclic oligomers

Comparison of the chemical shift data (Table 1) reveals that the peak positions of a and 6 carbons of 20-crown-4 are quite different from the corresponding carbons of THF or the polymeric PTME. Small but distinct chemical shift differences were also found for macrocyclic oligomers of other ring sizes. 

ROMP is generally an irreversible process, and relief of ring strain is the driving force for the forward reaction. Reversibility (with the formation of macrocyclic oligomers) is possible for less strained cycloalkenes like cyclooctene when the lifetimes for propagating chains are high. 

Finally, it has to be considered that also the formation of macrocyclic oligomers and polymers cannot be fully neglected. For example, by use of mass spectrometry, the existence of ring-shaped polycondensates is definitely elucidated in all types of polycondensates. 

In this case, however, attack by monomer at the carbon indicated with an asterisk would lead to a macrocyclic oligomer and a shortened propagating oxonium ion. This would be a true transfer reaction in that a smaller dead molecule is produced without any loss of active centers. 

Concerning a cyclic polymer of tetrahtydrofuran (THF), macrocyclic oligomers of THF were reported to be synthesized with Me30BF4 in CH3NO2 (the reaction is depicted in Fig. 35) [123]. 

Title Catalysts and Methods for Polymerizing Macrocyclic Oligomers... 

Tetraphenoxyl titanates such as 4-isopropyl-, 2-isopropyl-6-t-butyl-, and 2-di-t-butyl-have been prepared and used as catalysts for the rapid depolymerization and repolymerization of macrocyclic oligomers. In this manner macrocyclic co-esters consisting of (butylene terephthalate-co-ethylene terephthalate) were re-polymerized to molecular weights of up to 120,000 daltons. 

TABLE 1. Oligomer re-polymerization of macrocyclic oligomers using 0.3mol% tetraphenoxy titanates. 

The preparation and use of organotin compounds as re-polymerization agents for linear polyesters and macrocyclic oligomers is provided by Paler [1] and Winckler [2], respectively. 

Combinations of TT-allyl nickel chloride and bis(Tr-allyl) nickel produce macrocyclic oligomers from butadiene containing from four to above eight monomer units [138] in the absence of the chloride dimers and trimers only are produced. This is of interest in that termination occurs by ring closure rather than by hydrogen transfer. 

Under a variety of reaction conditions, such as high or low concentrations of reactants, high or low temperature, and polar or nonpolar solvents, macrocyclic oligomers 11 formed as the overwhelmingly major products. For example, little difference was found in the MALDI spectra of 11a before and after purification (Fig. 13). 

Another initiator for this polymerization is (Me3CO)3W=W(OCMe3)j, but analysis of the products by MS shows that they are macrocyclic oligomers. Their ring-size distribution, as determined by GPC, conforms to the Jacobson-Stockmayer relationship see Ch. 11. It is evident that with the tungsten catalyst... 

Calixarenes are conical-shaped macrocyclic oligomers whose inner cavity can accommodate several guest molecules and, therefore, can serve as a viable option to replace CDs in EKC separations. Environmental examples of the use of calixarene as EKC secondary phases include the separation of chlorinated phenols, benzenediols, and toluidines." Sulfonated calixarenes have also been used as chromophores in the indirect detection of aliphatic amines." ... 

A. Ben-Haida, H. M. Colquhoun, P. Hodge, and D. J. Williams. Synthesis of a catechol-based poly(ether ether ketone) ("o-PEEK") by classical step-growth polymerization and by entropically driven ring-opening polymerization of macrocyclic oligomers. Macromolecules, 39(19) 6467-6472, September 2006. 

Under the conditions of a kinetically controlled polycondensation reaction, cyclization reactions compete with propagation steps. The extent of cyclization depends on the flexibility of the polymer chain and on the concentration of the active species. Blends of PES with its homologous macrocyclic oligomers show greatly lowered melt viscosities in comparison to the corresponding original PES. 

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