Oligomers cyclic formal

Formally, isoprenoids are derived from a single common building block, isoprene (2-methyl-l,3-butadiene), a methyl-branched compound with five C atoms. Activated isoprene, isopentenyl diphosphate, is used by plants and animals to biosynthesize linear and cyclic oligomers and polymers. For the isoprenoids listed here—which only represent a small selection—the number of isoprene units (1) is shown. 

No data Formals of di-, tri-, tetraethylene glycols Extensive, fast cyclization in the presence of H0S02CF3 7-8). Kinetic enhancement observed (cf. Sect. 3.3). Concentration of lower cyclic oligomers (n = 2, 3, 4) high at the early stage of reaction, decreases in the course of the process. 

DXL and macrocyclic formals are the only cyclic acetals for which cyclization has been studied quantitatively.The formation of cyclic fraction may, however, be expected in the polymerization of any cyclic acetal. It has been indicated that cyclic oligomers are formed in the polymerization of TOX. Nonstabilized homopolymer always contains some amount (up to 25%) of a stable fraction, which, at least partially, is assumed to be cyclic (instability is related to the hemiacetal groups, which are absent in cyclic macromolecules). Cyclic oligomers are also believed to be responsible for the bimodal molecular weight distribution observed by GPC. ... 

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