Some Cyclic Oligomers

It has been demonstrated that simple 5-substituted isophthalic acid derivatives form well-defined cyclic hexameric aggregates of type 22 in the solid state that are 

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Mixing of oxetane (15 mmol) with 4 (0.3 mmol) in CH2CI2 (3 ml) in the absence of 1 under similar conditions resulted in a polymerization of oxetane, where the monomer conversion was stopped at 61.4% (2h), affording a broad MWD polymer (Mn 10, Mw/Mn=1.93) together with some cyclic oligomers... 

Some cyclic oligomers were formed as by-products in the polymerization of e-caprolactone. Yamashita et al. [136] reported that the anionic polymerization of e-caprolactone with f-BuOK in THF results in a living ring-chain... 

Readily soluble poly(2,9-o-phenanthroline-(2, 5 -dihexyl)-4,4"-p-ter-phenylene)s with a degree of polymerization up to 39 have been prepared via a Pd-catalyzed polycondensation reaction of 2,9-bis-(p-bromophenyl)-o-phenanthroline and 2,5-dihexylbenzene-l,4-diboronic acid [50]. Some cyclic oligomers could be separated from the polymer. Diamagnetic transition metal complexes of well-defined constitution as shown in 26 were obtained with Cu(I) and Ag(I) without branching and cross-linking. 

Based on model reactions for the preparation of poly(ethylene terephthalate) by ester interchange, the optimum molar ratio of ethvlene glycol to dimethyl terephthalate is 2.4 to 1. This ratio allows complete removal of methanol. The overall polyesteiification reaction is third order. In addition, high molecular weight polymerizations of poly(ethylene terephthalate) invariably produce some cyclic oligomers as byproducts. Eight different cyclic species were identified in one commercial polymer ... 

So far, it has proved difficult to polymerize cyclic oligomers that bear organic side groups only, but some species that bear both halogeno and organic side groups can be induced to polymerize. 

Cyclic oligomers of condensation polymers such as polycarbonates and polyesters have been known for quite some time. Early work by Carothers in the 1930s showed that preparation of aliphatic cyclic oligomers was possible via distillative depolymerization [1, 2], However, little interest in the all-aliphatics was generated, due to the low glass transition temperatures of these materials. Other small-ring, all-aliphatic cyclic ester systems, such as caprolactone, lactide... 

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