Chain condensation

The resulting silanol group of a polymer chain condenses with acetoxy siloxy group of another polymer chain to form a siloxane (Si-O-Si) linkage (Scheme 8). Further similar reactions finally result in a crosslinked elastomer. Acetic acid is... 

To avoid the obviously incorrect classification of polyurethanes as well as of some other polymers as addition polymers, polymers have also been classified from a consideration of the chemical structure of the groups present in the polymer chains. Condensation polymers have been defined as those polymers whose repeating units are joined together by functional... 

Alkylaromatic compounds possessing a sufficiently long side chain may also undergo dehydrocyclization.216 In fact, the aromatic ring enhances this reaction alkylaromatics undergo dehydrocyclization faster than do alkanes. Depending on the side chain, condensed or isolated ring systems may be formed. 

The prediction, kb (I) > h (III), probably holds for protodedeuteration, but its applicability to other displacements is less certain. As far as the displacement of the side chain at position 1 is concerned, it was already pointed out that, in protodedeuteration, side-chain condensation is more likely to occur. Side-chain displacement is common, however, in halogena-tion and nitration, and it seems reasonable to assume that the rates of these reactions may be controlled by the same factors controlling the displacement of hydrogen. On this basis unit III ought to be the most reactive in side-chain displacement while the reactivities of I and II are likely to be of the same order of magnitude. 

By a different type of side-chain condensation, the dimer 6995 was formed from l,2-dihydro-2,2,4-trimethylquinazoline in 0.1 N hydrochloric acid at 100°. Bimolecular reduction products have been produced when hydrogenating 3-acetamido-6-methoxy-5-nitropyridazine 2-oxide over palladium/charcoal two different products (70 and 71) have been isolated depending on the solvent used and the amount of hydrogen absorbed.96... 

The report by Curtis of the condensation of [Ni(en)3] + with acetone to give the open-chain condensation product and subsequently the macrocyclic complex (equation 8) was the first example of the synthesis of N-donor macrocycles by a metal template, and predates work on the oxycrown ligands such as 18-crown-6 ([18]ane06). 

The search for endothelin antagonists as potential compounds for treating cardiovascular disease was noted in Chapter 5 (see atrasentan). A composed with a considerably simpler structure incorporates a pyrimidine ring in the side chain. Condensation of benzophenone (94) with ethyl chloro-acetate and sodium methoxide initially proceeds to addition of the enolate from the acetate to the benzophenone carbonyl. The aUcoxide anion on the first-formed quaternary carbon then displaces chlorine on the acetate to leave behind the oxirane in the observed product (95). Methanolysis of the epoxide in the product in the presence of boron triflor-ide leads to the ether-alcohol (96). Reaction of this with the pyrimidine (97) in the presence of base leads to displacement of the methanesulfonyl group by the aUcoxide from 96. Saponification of the ester group in that product gives the corresponding acid, ambrisentan (98). " ... 

Diphenylsilicanediol in acetone containing a little ammonium hydroxide gives an oil at ordinary temperatures, which, when crystallised from chloroform and light petroleum, yields anhydrobisdiphenyl-silicanediol, M.pt, I1S° C., and soluble in 5 per cent, potassium hydroxide. Another experime nt carried out in tlie same way gave a compound, M.pt. 112° C., insoluble in potassium hydroxide solution. It was dianhydrotrisdiphenylsilieanedioL The products here are not closed chain condensation bodies,... 

Trianhydrotetrakisdiphenylsilicanediol crystallises in short, colourless prisms, M.pt. 128 5 C. It resembles the other two open-chain condensation products of diphenylsilicanediol. 

This figure shows the Influence of the hydrocarbon chain lengths on the phase behaviour of phosphatidylethanolamines (PEs) and lecithins (PCs). If the hydrocarbon chains are relatively short, monolayers are in the gaseous (G) or liquid-expanded (LE) state, while for sufficiently long chains condensed monolayers are formed. These monolayers are already in the coexistence state between gaseous (G) and condensed phase at a surface pressure of about zero and their x(A) isotherms exhibit no plateau region at accessible temperatures. In two cases increase of the surface pressure above a particular value k results in a first order phase transi-... 

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