Dicarboxylic acid ester diols

Polycondensation of diols with dicarboxylic acids is often performed in the melt. However, it does not always lead to high-molecular-weight polyesters. Sometimes, the starting materials or the resulting polyester are thermally unstable at the high condensation temperatures. If the reactants and the polyester are well soluble, one can carry out the polycondensation in solution (see Example 4-2). The elimination of water from diols and dicarboxylic acids frequently occurs rather slowly. In such cases suitable functional derivatives of the diols and dicarboxylic acids (esters or anhydrides) can be used instead of the direct condensation, as described in Sect. 4.1.1.3. 

Polycondensation of diols with dicarboxylic acids or reesterification of dicarboxylic acid esters with diols are the main methods of preparing polyesters. Because of the reversibility of this classical polyester formation, high reaction temperatures, long polycondensation times and low pressures are required to remove low molecular weight reaction products in order to shift the equilibrium to the direction of polyester formation and to obtain sufficiently high molecular weights. 

Preparation and Solubility of Polyesters. A number of polyesters were prepared from several diols and dicarboxylic acid esters to determine the effect of structure on the solubility in typical solvents used in lacquers. The data in Table I show that solubility in the solvents decreased in the following order toluene > methyl ethyl ketone > butyl acetate. Polymers that were soluble in all three solvents are examples 9-14. 

Various organic plasticizers having boiling points over 300 °C are available, such as di(2-ethylhexyl) phthalate (4a), di(2-ethylhexyl) adipate (8), oligomers formed from dicarboxylic acids and diols with molecular weights ranging up to 3500, esters of tri-mellitic acid, epoxidised fatty acids or organic phosphates, such as tris(2-ethylhexyl) phosphate (9) or (2-ethylhexyl) diphenyl phosphate (10). Most phosphates also function as flame retardants and some, such as 10, are smoke suppressants as well (Meier, 1990). 

The diisocyanates are used mainly in the manufacture of polyurethanes (PUR). These are produced by polyaddition of diisocyanates and dihydric alcohols, in particular the polyether alcohols (i.e., polyethylene glycols, polypropylene glycols, and the reaction products of propylene oxide with polyhydric alcohols). In addition, oligomeric esters from dicarboxylic acids and diols (polyester alcohols) are also used [91] ... 

Okumara et al. [10] were the first to attempt the enzyme-catalyzed synthesis of oligoesters from a reaction between dicarboxylic acids and diols. Gutman et al. [11] reported the first study on polyester synthesis by enzyme-catalyzed polymerization of A-B type monomers. Two independent groups in 1993 [12, 13] were first to report enzyme-catalyzed ring-opening polymerization (ROP). Their studies focused on 7- and 6-membered unsubstituted cyclic esters, e-caprolactone (e-CL) and 8-valerolactone (8-VL), respectively. 

Table 11.1-7. a-Chymostrypsin-catalyzed enantiotopos-differentiating hydrolysis of prochiral cyclic dicarboxylic acid esters, acyclic dicarboxylic acid esters and cyclic diol diacetates and enantiomer-differentiating hydrolysis of racemic carboxylic acid esters in aqueous solution. 

Ester Exchange. The most practical methods for the preparation of high molecular weight polyesters involve ester exchange reactions. The simplest exchange method involves a catalyzed alcoholysis reaction between a diol and a dicarboxylic acid ester with elimination of the alcohol ... 

As an example of a more complicated case than the two step sequence, we will discuss the esterification of a carboxylic acid with an alcohol. This is a very old and well-known category of homogeneous liquid-phase reactions. The esters of carboxylic acids are of an enormous practical importance for example, millions of tons of polyesters are produced via the reaction of dicarboxylic acids with diols and a wide variety of mono- and di-esters are used in the production of fine and specialty chemicals, such as pharmaceuticals, herbicides, pesticides and fragrances. The esterification reaction is a homogenous liquid-phase process where the limiting conversion of the reactants is determined by equilibrium. Typically the equilibrium constants of esterification reactions have values of 1-10, which implies that considerable amounts of reactants exist in the equilibrium mixture. 

Polyesters contain the ester group —COO— in the main chain. Many methods are suitable for their synthesis self-condensation of a,o>-hydroxy acids, ring-opening polymerization of lactones, the polycondensation of dicarboxylic acids with diols, transesterification, the polycondensation of diacyl chlorides with diols, polymerization of O-carboxy anhydrides of a- and jS-hydroxycarboxylic acids, and the copolymerization of acid anhydrides with cyclic ethers. The last reaction is commercially used in the curing of epoxides with anhydrides. 

Polycondensation reactions are equilibrium reactions. In most polycondensations, the condensation equilibrium is actually reached. Polycondensations usually take place through the elimination of a low-molecular-weight component. The polycondensation of dicarboxylic acids with diols is an example. According to the law of mass action, the concentrations of water, carboxyl, hydroxyl and ester groups are related by... 

The second method of obtaining organic polymers involves the exploitation of functional group chemistry of organic molecules. Thus, for example the reaction of a carboxylic acid with an alcohol affords an ester. Instead of condensing two mono functional derivatives in reacting two difunctional compounds (dicarboxylic acids and diols) one obtains a polyester see Bq. 1.1). 

The reaction of an alcohol with a vinyl ester proceeds much faster than with an alkyl ester or a haloalkyl ester to form the desired product in higher yields Kobayashi and co-workers [36-41] studied the polymerisation of the divinyl esters of dicarboxylic acids with diols, triols and sorbitol. The polymerisation behaviour was strongly dependent on the monomer structure, enzyme origin and reaction conditions. Under appropriate conditions, an aliphatic polyester with a MW higher than 2 x lO Da was obtained. The polymerisation of divinyl adipate with 1,4-BDO by PFL, in isopropyl ether at 45 °C for 48 h, produced a polyester with a MW of 6,700 Da and a yield of 50% (Scheme 12.8, [1]), whereas the use of CAL was also employed to produce crosslinkable polyesters [40]. Divinyl sebacate and glycerol were polymerised in the presence of the unsaturated fatty acids, oleic acid, linoleic acid and linoleinic acid. NMR analysis revealed that the reaction proceeded with regioselectivity during the... 

Some plasticisers based on dicarboxylic acids may not only be esters but also salts. The infrared spectra of these plasticisers obviously contain the bands associated with both esters and carboxylic acid salts. This means that it is difficult to distinguish between a compound and a mixture of an ester and salt. In a similar fashion, it is difficult to distinguish between plasticisers based on dicarboxylic acids and diols and polyesters based on similar compounds. There are no easily recognisable spectral features to distinguish between monomeric esters and an equivalent polyester. 

Polyesters are a second class of condensation polymers and the principles behind their synthesis parallel those of polyamides Ester formation between the functional groups of a dicarboxylic acid and a diol... 

Plasticizers can be classified according to their chemical nature. The most important classes of plasticizers used in rubber adhesives are phthalates, polymeric plasticizers, and esters. The group phthalate plasticizers constitutes the biggest and most widely used plasticizers. The linear alkyl phthalates impart improved low-temperature performance and have reduced volatility. Most of the polymeric plasticizers are saturated polyesters obtained by reaction of a diol with a dicarboxylic acid. The most common diols are propanediol, 1,3- and 1,4-butanediol, and 1,6-hexanediol. Adipic, phthalic and sebacic acids are common carboxylic acids used in the manufacture of polymeric plasticizers. Some poly-hydroxybutyrates are used in rubber adhesive formulations. Both the molecular weight and the chemical nature determine the performance of the polymeric plasticizers. Increasing the molecular weight reduces the volatility of the plasticizer but reduces the plasticizing efficiency and low-temperature properties. Typical esters used as plasticizers are n-butyl acetate and cellulose acetobutyrate. 

Polyesters can be produced by an esterification of a dicarboxylic acid and a diol, a transesterification of an ester of a dicarboxylic acid and a diol, or by the reaction between an acid dichloride and a diol. 

From the preceding discussion, it is easily understood that direct polyesterifications between dicarboxylic acids and aliphatic diols (Scheme 2.8, R3 = H) and polymerizations involving aliphatic or aromatic esters, acids, and alcohols (Scheme 2.8, R3 = alkyl group, and Scheme 2.9, R3 = H) are rather slow at room temperature. These reactions must be carried out in the melt at high temperature in the presence of catalysts, usually metal salts, metal oxides, or metal alkoxides. Vacuum is generally applied during the last steps of the reaction in order to eliminate the last traces of reaction by-product (water or low-molar-mass alcohol, diol, or carboxylic acid such as acetic acid) and to shift the reaction toward the... 

Dicarboxylic acids or esters thereof are recovered from solid phase polyester materials, such as post-consumer products and factory scrap, by subjecting the polyester to at least two hydrolysis stages in at least the first of which the amount of water used is substantially less than needed to effect total conversion of the polyester to the dicarboxylic acid. Also the diol content is controlled in the course of carrying out the hydrolysis. The hydrolysis reactions may be preceded by reaction of the polyester with a diol, the resulting depolymerisation products then being hydrolysed. 

Polymerisation of a diol with a dicarboxylic acid is exemplified by the production of a polyester from ethylene glycol and terephthalic 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 resiliency its structure is probably ... 

High boiling polar compounds, diols, phenols, methyl esters of. dicarboxylic acids, amines, diamines, ethanolamines, amides, aldehydes and ketones. 

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