Polyethers synthesis methods

A priori, there are two possibilities for synthesising the polyarylene sulphones. Either a polyether synthesis could be used to join up the aryl sulphone intermediates with ether linkages or a polysulphonylation process employed to link up aryl ethers. In practice either method can be used and will give polymers of hi molecular wei t provided that the intermediates are selected tfithin certain structuiml limitations and the reactim conditions are closdy controlled. The methods are quite different chemically and a polymer structiire made by one route cannot usually be made by the other, althou some structures can be made by either process. 

Almost all of the known thermotropic L polymers are polyethers, and the primary method of their synthesis is polycondensation, in some cases polyaddition. We will examine the methods of synthesis, methods of determining the L state, some typical structure-property dependences, and the structure and practical apphcation of L polymers below. The initial model of the chain structure selected, which consists of altmiating rigid and flexible fragments (or kinks, hinges), predetermines the possibility of considering them as copolymers. 

The compound known as 18-crown-6 is one of the simplest and most useful of the macrocyclic polyethers. Its synthesis in low yield was first reported by Pedersen. Greene and Dale and Kristiansen" have reported syntheses of the title compound from triethylene glycol and triethylene glycol di-p-toluenesulfonate. Both of these procedures use strong base and anhydrous conditions and achieve purification by more or leas classical methods. The combination of distillation and formation of the acetonitrile complex affords crown of high purity without lengthy chromatography or sublimation. ... 

In Pedersen s first full paper on the synthesis of macrocyclic polyethers, he reported the synthesis of thirty-three macrocycles having a variety of ring sizes and substituents. These compounds were prepared by a variety of routes and Pedersen offered a scheme in which he generalized the synthetic approaches he used. He designated the four principal methods V , W , X , and Y . The methods are diseussed individually. 

In the course of experiments directed at the synthesis of open-chained equivalents of macrocyclic polyethers (see Chap. 7), Rasshofer and Vogtle found that 9 or its derivatives were formed rather than the desired compounds . Although the yields obtained by this method are modest, the facts that the reaction is conducted without the use of high dilution and in one-pot recommend it. 

It is interesting to note that all the new aromatic systems, as described, undergo displacement polymerizations in DMAC solvent by the K2CO3 method, except perfluoroalkylene [10] and amide activated polymerization [9], which were performed in NMP solvent. The displacement polymerization in DMAC solvent was carried out at 155-164°C. poly(aryl ether ketones) require less reaction time (3-6 h) than other aromatic systems for synthesis of polyethers [15]. Synthesis of the fluorinated polyether as reported by Irvin et al. [16] was carried out at room temperature for 16 h (Mw = 75,000), whereas the same polymer by Mercer et al. [17] was synthesized at 120°C for 17 h (Mw = 78,970). 

Synthesis of all these heterocycle activated polyethers is carried out in polar aprotic solvents, such as NMPs, by the K2CO3 method. The effective displacement reactions are reported at varied temperatures (140-190°C) and durations (3-24 h). 

The Prelog-Djerassi lactone (abbreviated here as P-D lactone) was originally isolated as a degradation product during structural investigations of antibiotics. Its open-chain equivalent 3 is typical of the methyl-branched carbon chains that occur frequently in macrolide and polyether antibiotics. The compound serves as a test case for the development of methods of control of stereochemistry in such polymethylated structures. There have been more than 20 different syntheses of P-D lactone.24 We focus here on some of those that provide enantiomerically pure product, as they illustrate several of the methods for enantioselective synthesis.25... 

Acyclic stereocontrol has been a striking concern in modern organic chemistry, and a number of useful methods have been developed for stereoregulated synthesis of conformationally nonrigid complex molecules such as macrolide and polyether antibiotics. Special attention has therefore been paid to the aldol reaction because it constitutes one of the fundamental bond constructions in biosynthesis. 

This paper reviews some of our work on general methods for the synthesis of polyaromatics containing either terminal or pendant styrene groups and their thermal polymerization. The examples provided in this paper refer to an aromatic polyether sulfone (PSU) and poly-(2,6-dimethy1-1,4-phenylene oxide) (PPO). 

Three major topics of research which are based on phase transfer catalyzed reactions will be presented with examples. These refer to the synthesis of functional polymers containing functional groups (i.e., cyclic imino ethers) sensitive both to electrophilic and nucleophilic reagents a novel method for the preparation of regular, segmented, ABA triblock and (A-B)n alternating block copolymers, and the development of a novel class of main chain thermotropic liquid-crystalline polymers, i.e., polyethers. 

Hyperbranched polymers are formed by polymerization of AB,-monomers as first theoretically discussed by Flory. A wide variety of hyperbranched polymer structures such as aromatic polyethers and polyesters, aliphatic polyesters. polyphenylenes, and aromatic polyamides have been described in the literature. The structure of hyperbranched polymers allows some defects, i.e. the degree of branching (DB) is less than one. The synthesis of hyperbranched polymers can often be simplified compared to the one of dendrimers since it is not necessary to use protection/deprotection steps. The most common synthetic route follows a one-pot procedure " where AB,-monomers are condensated in the presence of a catalyst. Another method using a core molecule and an AB,-monomer has been described. ... 

An improved procedure for cyclopalladation-carbonylation (of e.g. 320) relies on the addition of CuCl and LiCl to the standard PdCl2-CuCl2 mixture. This indicates that both the Cu2+ and Cu+ are required in sufficient concentrations to keep up the cascade of the catalytic cycle. This method is superior to the Hg(II)-mediated cyclization followed by transmetallation with Pd in CO/MeOH197. For application in the synthesis of polyether antibiotics, see elsewhere435. 

Allylic alcohols may also be formed from their corresponding halides by reaction with either peracids222 or potassium superoxide and a crown ether223. This latter methodology has been used in the synthesis of a polyether antibiotic, containing an allylic alcohol and a spiroacetal, where other methods have failed223. During allylic halide conversion, allylic... 

The high diastereoselectivity attending the spirocyclisation of ketene dithioacetals provides an effective means for controlling the stereochemistry of a methyl substituent at the a-position on a 6-lactone ring,244 The method was applied to the synthesis of the polyether antibiotic Salinomycin [Scheme 2.120].242 Condensation of the methyl ketone 120 1 with the lithiated l,3-dithian-2-yl-phospho-nic acid diethyl ester 120.2 gave the ketene dithioacetal 1203 in 76% yield. After hydrolysis of the two benzoate ester groups, cyclisation of diol 120.4 was... 

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