Ethylene cyclic oligomers formation

Peebles, L. H., Huffman, M. W. and Ablett, C. T., Isolation and identification of the linear and cyclic oligomers of poly(ethylene terephlhalate) and the mechanism of cyclic oligomer formation, J. Polym. ScL, PartA-1, 7, 479 (1969). 

Cyclic oligomer formation during polycondensation has been studied for the ethylene glycol-adipic acid system and oxycycloeicosanone has been identified. Similarly, oligomers have been isolated and identified from the preparation of poly(butylene glycol terephthalate). ... 

The operation of the mismatch effects may be seen to best advantage when a range of products is possible from a single reactant or set of reactants. The reaction of ethylene oxide with metal salts results in the formation of crown ethers (Fig. 6-30). Obviously, a whole range of different cyclic oligomers and acyclic polymers could be formed from ethylene oxide. If we specifically wanted to obtain 18-crown-6, with a hole size of about 1.4 A, we would expect to use a potassium ion as template (r = 1.38 A). In fact, 18-crown-6 is obtained in good yield from the reaction of ethylene oxide with potassium tetra-fluoroboratc. In contrast, if we wanted 12-crown-4, with a hole size of about 0.8 A, it... 

A side reaction often occurring in polycondensation reactions that take place in the molten state is the formation of cyclic oligomers. As already mentioned (Section 5.2), this is an important group of reactions in the preparation of poly(ethylene terephthalate). The reactions that lead to cyclooligomerization are, of course, not degradative the cyclic material is in equilibrium with linear polymer molecules. 

Evidence for the back-biting reaction is the formation of cyclic oligomers during the ring-opening polymerization of some heterocyclic monomers (81. 84-87). The classic example is dioxane formation during polymerization of ethylene oxide. 

The small contribution of macrocyclization in the polymerization of THF is due to two effects The formation of smaller cyclic oligomers like dimer and trimer is thermodynamically unfavorable (in contrast to the formation of e.g. 1,4-dioxane in the polymerization of ethylene oxide) because 10- and 15-membered cyclic ethers are strained. It is also kinetically hampered since the rate of chain transfer to polymer which leads to ring formation is low due to the lower basicity of the polymer units than that of THF. 

It may be noted that besides chemical crosslink formation we can achieve the physical linking of macromolecules (Fig. 6) where the effect on propoties could be just as important as in chemical aosslinking and entanglements. The pertinence of such a procedures may be demonstrated by the synthesis of polyrotaxanes [197] in which a cyclic oligomer of ethylene oxide is absorbed on macromolecules of polyami (Scheme 1)... 

Table 5 shows the results of complex formation between a-CD and cyclic oligomers of ethylene glycol, together with those of linear OEG for comparison. It is interesting that the yields of the complexes of a-CD with cyclic OEG decreased with an increase in the size of the guest, and those of the... 

Polyalkylene polyamines are typical by-products in the amination of dihydroxy compounds. Some of these oligomers, e. g. diethylenetriamine and triethylene-tetramine, are valuable compounds they are produced industrially from ethanol-amine (sometimes directly from ethylene oxide) and ammonia or a mixture of ammonia and ethylenediamine. Over a Ni-Re boride catalyst the selectivity for diethylenetriamine was ca 25 %, almost independent of the conversion [27]. Higher temperatures favored the formation of worthless cyclic products, mainly piperazine and its N-alkylated derivatives (Scheme 9). Recycling the cyclic byproducts can minimize their formation and the higher oligomers can be decomposed to useful dimers and trimers [26]. 

Surface Oligomer Detection and Imaging. The case of cyclic trimer (three monomers in a ring formation) on the surface of poly(ethylene terephtha-late) (PET) film is interesting. The crystallization of cyclic trimer on PET surfaces... 

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