Polyethylene cyclic

Reinhoudt, Gray, Smit and Veenstra prepared a number of monomer and dimer crowns based on a variety of substituted xylylene units. They first conducted the reaction of 1,2-dibromomethylbenzene and a polyethylene glycol with sodium hydride or potassium Z-butoxide in toluene solution. Mixtures of the 1 1 and 2 2 (monomer and dimer) products were isolated and some polymer was formed . The reaction was conducted at temperatures from 30—60° and appeared to be complete in a maximum of one hour. The authors noted that the highest yield of 1 1 cyclic product was obtained with disodium tetraethylene glycolate instead of dipotassium hexaethylene gly-colate (see also Chap. 2) . Chloromethylation of 1,3-benzodioxole followed by reaction with disodium tetraethylene glycolate afforded the macrocycle (29% yield) illustrated in Eq. (3.20). 

It was noted early by Smid and his coworkers that open-chained polyethylene glycol type compounds bind alkali metals much as the crowns do, but with considerably lower binding constants. This suggested that such materials could be substituted for crown ethers in phase transfer catalytic reactions where a larger amount of the more economical material could effect the transformation just as effectively as more expensive cyclic ethers. Knbchel and coworkers demonstrated the application of open-chained crown ether equivalents in 1975 . Recently, a number of applications have been published in which simple polyethylene glycols are substituted for crowns . These include nucleophilic substitution reactions, as well as solubilization of arenediazonium cations . Glymes have also been bound into polymer backbones for use as catalysts " " . 

The chemical and physical properties of the polymers obtained by these alternate methods are identical, except insofar as they are affected by differences in molecular weight. In order to avoid the confusion which would result if classification of the products were to be based on the method of synthesis actually employed in each case, it has been proposed that the substance be referred to as a condensation polymer in such instances, irrespective of whether a condensation or an addition polymerization process was used in its preparation. The cyclic compound is after all a condensation product of one or more bifunctional compounds, and in this sense the linear polymer obtained from the cyclic intermediate can be regarded as the polymeric derivative of the bifunctional monomer(s). Furthermore, each of the polymers listed in Table III may be degraded to bifunctional monomers differing in composition from the structural unit, although such degradation of polyethylene oxide and the polythioether may be difficult. Apart from the demands of any particular definition, it is clearly desirable to include all of these substances among the condensation... 

Cyclic polyethylene oxides) ( Crown ethers ), Potassium hydroxide Le Goaller, R. etal., Synth. Comm., 1982, 12, 1163-1169 Crown ethers promote dihalocarbene formation from chloroform or bromoform and potassium hydroxide. However, in absence of diluent dichloromethane, dropwise addition of bromoform to the base in cyclohexane led to explosions. 

Bromoform, Potassium hydroxide See Bromoform Cyclic polyethylene oxides), etc. 

The molecular design of stereospecific homogeneous catalysts for polymerization and oligomerization has now reached a practical stage, which is the result of the rapid developments in early transition metal organometallic chemistry in this decade. In fact, Exxon and Dow are already producing polyethylene commercially with the help of metallocene catalysts. Compared to the polymerization of a-olefins, the polymerization of polar vinyl, alkynyl and cyclic monomers seems to be less developed. 

Acidic chloroaluminate ionic liquids are excellent media for polymer cracking reactions. With the huge quantities of polymers that need to be disposed of each year the ability to break them down into useful compounds for new synthesis or to use as liquid fuels is extremely important. While certain polymers such as poly(methyl methacrylate) are easily cracked into their constituent monomers that can be reused, the majority of polymers are extremely difficult to crack into useful organic compounds. However, merely dissolving polyethylene in acidic chloroaluminate ionic liquids containing a proton source results in the formation of a mixture of alkenes and cyclic alkenes [48], The key compounds produced are shown in Figure 10.10. 

Peebles, L. H., Huffmann, M. W. and Ablett, C. T Isolation and identification of the linear and cyclic oligomers of polyethylene terephthalate... 

Cooper, D. R. and Semiyen, J. A., Equilibrium ring concentrations and the statistical conformations of polymer chains part 11. Cyclics in polyethylene terephthalate), Polymer, 14, 185 (1973). 

The workhorse polyester is polyethylene terephthalate) (PET) which is used for packaging, stretch-blown bottles and for the production of fibre for textile products. The mechanism, catalysis and kinetics of PET polymerization are described in Chapter 2. Newer polymerization techniques involving the ring-opening of cyclic polyester oligomers is providing another route to the production of commercial thermoplastic polyesters (see Chapter 3). 

As cyclic polyethers (polyethylene oxides), some of this group of aprotic complexing solvents may be subject to peroxidation, though no reports have been so far noted. 

Begley, T.H., Dennison, J.L. and Hollifield, H.C. (1990). Migration into food of polyethylene terephthalate (PET) cyclic oligomers from PET microwave susceptor packaging. Food Addit. Contain., 7, 6, 797-803. 

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