Cyclic ethers polymers

Vinylidene chloride-vinyl chloride polymers are also self-extinguishing and possess very good resistance to a wide range of chemicals, including acids and alkalis. They are dissolved by some cyclic ethers and ketones. 

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 " " . 

A variety of cyclic ethers, 410, have been obtained via both, solution-phase and polymer-supported methods in the [3 + 2] cycloadditions of nitrile oxides to alkenes and dienes to give isoxazolines (Scheme 1.50). Both simple and substituted dienes have been found suitable for polymer-supported formation of cyclic ethers of ring sizes five through seven (449). 

However, for a variety of reasons it seems extremely unlikely that the same mechanism is applicable to the polymerisation of cyclic formals and acetals. One reason is that these compounds cannot be co-polymerised with cyclic ethers another is that the polymers are predominantly cyclic, with the number of end-groups far smaller than the number of growing chains. One mechanism which has been proposed and which accounts for most of the observations involves formation of an oxonium ion (X) from the initiator and the monomer, and a subsequent propagation by a ring-expansion reaction (see 13). 

Schaefer and Natusch have shown that for many synthetic high polymers in solution the NOE factors and relaxation times of carbon atoms in or near the main chains eire similcir (.2. In such cases the relative peak areas in the spectra obtained by the noise-decoupled and fast pulsing technique can be used as a good approximation for quantitative microstructure euialysis. However for our investigation of the polymerization of cyclic ethers we are frequently interested in the quantitative measurements of monomers and oligomers as well as the concentrations of the continuously growing polymeric species. Therefore, the assumption of Schaefer and Natusch is not applicable. 

A linear phenylene-ethylene copolymer is obtained by a Wurtz-type condensation of 1,2-dibromoethane and 1,4-dibromobenzene. A cross-linked variation can be obtained on addition of 1,3,5-tribromobenzene to the reaction mixture. Equation 119 illustrates the reductive scission of a cyclic ether, catalyzed by such polymers in the presence of lithium, followed by quenching with cyclohexanone . 

Many other cyclic ethers have been polymerized using cationic polymerization. Ethylene oxide (also called oxirane) polymerizes forming poly(ethylene oxide) (PEO) (structure 5.24) in the presence of acids such as sulfuric acid, producing a wide range of chain-sized polymers sold under various trade names including Carbowax and Poly ox. PEO is also used in cosmetics and pharmaceuticals (as water-soluble pill coatings and capsules). 

Transfer and termination occur by the modes described previously for cyclic ether polymerizations. Chain transfer to polymer (both inter- and intramolecular) is facilitated in cyclic acetal polymerizations compared to cyclic ethers because acetal oxygens in the polymer chain are more basic than the corresponding ether oxygens [Penczek and Kubisa, 1989a,b]. Working at high monomer concentrations, especially bulk polymerizations, is used to depress cyclic oligomer formation. 

Takata and Endo, 1988]. A cyclic carbonate and cyclic ether are eliminated as by-products in reaction pathways a and b, respectively. Polymer LXXIV contains both ether and carbonate functional groups in the polymer chain. 

Polymerization of four-membered cyclic ethers (oxetanes) is also brought about by cationic initiators (e.g., Lewis acids) and by anionic initiators (e.g., or-ganometallic compounds). The polymer of 3,3-bis(chloromethyl)oxetane is distinguished by its very high softening point and by its unusual chemical stability. 

Polyethers are prepared by the ring opening polymerization of three, four, five, seven, and higher member cyclic ethers. Polyalkylene oxides from ethylene or propylene oxide and from epichlorohydrin are the most common commercial materials. They seem to be the most reactive alkylene oxides and can be polymerized by cationic, anionic, and coordinated nucleophilic mechanisms. For example, ethylene oxide is polymerized by an alkaline catalyst to generate a living polymer in Figure 1.1. Upon addition of a second alkylene oxide monomer, it is possible to produce a block copolymer (Fig. 1.2). 

Tetrahydrofuran, a five-member cyclic ether, polymerizes cationically to yield an elastomeric polymer [28]. Oxepane, a seven-member analog, polymerizes to a crystalline polymer. 

Price has studied the thermal and photodecomposition of 3.5-dimethyl-1.4-diazooxide under a variety of conditions (52). No polymers were obtained except when the decomposition was nm in cyclic ethers. Under these conditions low molecular weight materials in which considerable amounts of solvent were incorporated were obtained. Similar results have been obtained by Stille (78). 

The most import uni cyclic ethers arc (he furan compounds Furfural is manufactured by treating pentosan with sulfuric acid and steam stripping mil the furfural a n is formed The sources of pentosan arc such agricultural products uv comet tbs. oat hulls, and hagavtc Furfural is used to produce furan and tetrahydro furan fTHF) These products are used as organic intermediates, extraction solvent, polymer solvents, and in polyurethane applications... 

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