Ester interchange reactions

Polymerisation of a diol with a dicarboxybe acid is exemplified by the production of a polyester from ethylene glycol and terephthabc acid either by direct esterification or by a catalysed ester-interchange reaction. The resulting polyester (Terylene) is used for the manufacture of fibres and fabrics, and has high tensile strength and resibency its structure is probably ... 

Ester interchange reactions are valuable, since, say, methyl esters of di-carboxylic acids are often more soluble and easier to purify than the diacid itself. The methanol by-product is easily removed by evaporation. Poly (ethylene terephthalate) is an example of a polymer prepared by double application of reaction 4 in Table 5.3. The first stage of the reaction is conducted at temperatures below 200°C and involves the interchange of dimethyl terephthalate with ethylene glycol... 

Mixed esters can be prepared from Cl Ti(OR)4 and a second alcohol in the presence of a base or by mixing a tetraalkoxide and the second alcohol in the desired proportions and flash-evaporating the mixed alcohols. Mixing of two pure tetraalkoxides of titanium also leads, via a rapid ester interchange reaction, to a mixture of ah. possible combinations of tetraalkyl titanates. 

In 1930 Carothers and Natta prepared a number of aliphatic polycarbonates using ester-interchange reactions. These materials had a low melting point, were easily hydrolysed and did not achieve commercial significance. 

Transesterifications, also termed ester exchange or ester interchange reactions, include hydroxy-ester, carboxy-ester, and ester-ester reactions. Hydroxy-ester reaction is the most important one and is used for many aromatic-aliphatic and wholly aromatic polyester syntheses. Carboxy-ester interchange is restricted to the synthesis of wholly aromatic polyesters while the ester-ester route is rarely used for polyester preparation due to slow kinetics. All these reactions may take place in comparable experimental conditions and can be catalyzed by similar classes of compounds. 

Since 1,4-butanediol (BD) undergoes dehydration side reaction in the presence of acid resulting in THF formation, the hydroxy-ester interchange reaction is the preferred method for the preparation of PBT. The first stage of reaction is carried out at 150-200°C and consists of a hydroxy-ester interchange between DMT and excess butanediol with elimination of methanol. In the second stage, temperature is raised to 250°C and BD excess is eliminated under vacuum. Tetraisopropoxy-and tetrabutoxytitanium are efficient catalysts for bodi stages (Scheme 2.20). 

Many random copolyesters and polyester-polycarbonates have also been prepared by ester interchange reactions in the molten state. Thus, poly(ethylene terephthalate-co -isophthalates) can be obtained by simple melt blending of PET and poly(ethylene isophthalate) (PEI) homopolyesters at 270°C. The copolymer changes gradually from a block type at the beginning of reaction to a random-type... 

The dimethyl ester of a carboxy-terminated diamide is reacted with 1,2-ethanediol in the conditions of PBT synthesis. The amide functions are unaffected while the hydroxy-ester interchange reaction proceeds to the formation of an alternating copolyesteramide (Scheme 2.60). The procedures given below are reproduced from ref. 430. (Copyright 1997 Elsevier Science Ltd, with permission of the copyright owner.)... 

This synthesis involves the hydroxy-ester interchange reaction between phenyl ester and phenol endgroups436 (Scheme 2.63) (see Section 2.3.2.2). 

Carbonyldlimidazolc, 78 Carbonyl-metal interactions, 74 Carbosiloxadienes, 452 Carboxy-ester interchange melt polyesterification, 113 Carboxy-ester interchange reactions, 62, 64, 69, 74... 

Estane VC products, 201 Ester-amide copolymers, 146, 147 Esterases, 82 Esterification, direct, 63 Ester interchange catalysts, 71 Ester interchange reactions, 31, 62-63,... 

Hydroxybenzylamine intermediates, 392 Hydroxybenzylamines, 389, 391, 416 thermal decomposition of, 392 Hydroxy-ester interchange reactions, 62, 65, 69-74, 84, 111 Hydroxy-functional crosslinkers, 214 Hydroxyl endgroup chemical titration, 94-95... 

Interchange reactions, 40, 62, 64. See also Ester interchange reactions ADMET, 437-438... 

Hydroxymethylation (formaldehyde) of nitro-imidazole 76 affords 77, which is oxidized to aldehyde 78. To prepare the other fragment for this convergent synthesis, reaction of epichlorohydrin with morpholine leads to the aminoepoxide 79, which is reacted with hydrazine to afford 80. Reaction of this substituted hydrazine with dimethyl carbonate affords oxazolinone 81 by sequential ester interchange reactions. Condensation of 81 with aldehyde 78 affords the antitricho-... 

Elenga el al. [78] observed a drastic loss of drawability, together with a significant increase in strength at yield, for PET annealed for long periods of time. They attributed this to ester interchange reactions, which turn chain folds into intercrystalline tie molecules between neighbouring lamellae. 

Finally, annealing studies have shown that chemical reaction at the crystal surface is possible, changing both the crystal surface and the molecular chain [82], In addition, PET samples have been shown to undergo ester-interchange reactions at temperatures above 200 °C, with the rate of reaction becoming relatively high only at temperatures above 225 °C [83],... 

Droscher, M. and Schmidt, F. G The kinetics of the ester-interchange reaction of polyethylene terephthalate, Polym. Bull., 4, 261-266 (1981). 

Hydrolysis of Copolyamide-esters (CPAEs) by Lipase (jj,). CPAEs were synthesized by the amide-ester interchange reaction between polyamide and polyester. The length of the polyamide blocks was measured after hydrolysis of ester bonds in CPAE by alkali at 30 C. The infrared spectra after hydrolyzing ester bonds on CPAEs showed that the ester bonds were almost completely removed. The molecular weight distribution of polyamide blocks was examined by GPC (Table II). The following samples were used CPAE-1 (reaction time for synthesis, 1 hr) and CPAE-2 (reaction time, U hr) composed of nylon 6 and PCL at a 50/50 molar ratio, CPAE-3 (reaction time, 1 hr) and CPAE-U (reaction time,... 

If the fractional conversion in an ester interchange reaction is 0.99999, what would be the average degree of polymerization of the polyester produced ... 

Because of the difficulty encountered in removing the water that is produced when an acid reacts with an alcohol, PET is produced commercially by the reaction of dimethyl terephthalate, the dimethyl ester of terephthalic acid, with ethylene glycol in an ester interchange reaction. The methanol that is formed in this reaction is readily removed by distillation. 

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