Dicarboxylic acids polyesterification

Asin L, Armelin E, Montane J, Rodriguez-Galan A, Puiggali J (2001), Sequential poly(ester amide)s based on glycine, diols and dicarboxylic acids Polyesterification versus interfacial polyamidation , J. Pol. Sci. Part A Chemistry, 39 (24), 4283-4293. 

Linear step-growth polymerizations require exceptionally pure monomers in order to ensure 1 1 stoichiometry for mutually reactive functional groups. For example, the synthesis of high-molecular-weight polyamides requires a 1 1 molar ratio of a dicarboxylic acid and a diamine. In many commercial processes, the polymerization process is designed to ensure perfect functional group stoichiometry. For example, commercial polyesterification processes often utilize dimethyl terephthalate (DMT) in the presence of excess ethylene glycol (EG) to form the stoichiometric precursor bis(hydroxyethyl)terephthalate (BHET) in situ. 

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... 

Sulfur compounds have also been widely studied as activating agents for polyesterification reactions. p-Toluenesulfonyl chloride (tosyl chloride) reacts with DMF in pyridine to form a Vilsmeir adduct which easily reacts with carboxylic acids at 100-120° C, giving highly reactive mixed carboxylic-sulfonic anhydrides.312 The reaction is efficient both for aromatic dicarboxylic acid-bisphenol312 and hydroxybenzoic acid314 polyesterifications (Scheme 2.31). The formation of phenyl tosylates as significant side products of this reaction has been reported.315... 

While most of the kinetic relationships derived in the preceding sections have referred to polyesterification reactions between a dicarboxylic acid and a glycol, extension to other step-growth polymerizations of bifunctional monomers can be done in a straightforward manner. 

After this general presentation of the synthetic methods for obtaining polyester polyols, the direct polyesterification of dicarboxylic acids with glycols, the most important route to polyester polyols will be presented in detail. 

Table 8.1 shows the most important polyols (diols and triols) and Tables 8.2 and 8.3 show the most important dicarboxylic acids used as raw materials for direct polyesterification reactions. 

It is possible to obtain polyester polyols based on AA and two different diols, such as AA-EG/BD and AA-HD/NPG. Other possibilities are to develop the polyesterification with one glycol type and two different dicarboxylic acids, such as AA/IPA-HD or AA/ IPA-NPG/HD. These polyester polyols containing some aromatic groups of IPA are used on floor coatings and in adhesives. 

The synthesis of dimeric fatty acids is based on the reaction between a fatty acid with one double bond (oleic acid) and a fatty acid with two double bonds (linoleic acid) or three double bonds (linolenic acid), at higher temperatures in the presence of solid acidic catalysts (for example montmorillonite acidic treated clays). Dimerised fatty acids (C36) and trimerised fatty acids (C54) are formed. The dimer acid is separated from the trimeric acid by high vacuum distillation. By using fatty dimeric acids and dimeric alcohols in the synthesis of polyesters and of polyester polyurethanes, products are obtained with an exceptional resistance to hydrolysis, noncrystalline polymers with a very flexible structure and an excellent resistance to heat and oxygen (Chapter 12.5). Utilisation of hydrophobic dicarboxylic acids, such as sebacic acid and azelaic acid in polyesterification reactions leads to hydrolysis resistant polyurethanes. 

Polyesterification by acidolysis ester exchange is also a useful synthetic method, for example, reaction of the diacetate ester of a dihydric phenol with a dicarboxylic acid in the presence of a catalyst to eliminate acetic acid. 

The esterified partial oxidation products formed during the esterification process have significantly lower boiling points than the esters of the dicarboxylic acid. Thus, without any intervening chemical treatment, such as hydrogenation or treatment with sulfite, crude aryl dicarboxylic acids can be purified by esterification followed by disdllation. The purified dicarboxylic acid esters can then be subjected to direct polyesterification to produce the polyester resin. ... 

Figure 7 presents polycondensation using the example of polyesterification. As in the reaction illustrated above of ethanol and ethanoic (acetic) acid, producing acetic acid ethylester (ethyl acetate), only the functional groups are essentially important in describing esterification. Bifunctional monomers are required for polycondensation. In the example of polyesterification, diols such as ethandiol (glycol) and dicarboxylic acids such as terephthalic acid are used. 

The catalytic activity of the acid catalyst is due to hydrogen ions [55]. In the presence of a strong acid catalyst (e.g., p-toluene sulfonic acid), hydrogen ions are produced mainly from the added acid. Thus the polyesterification is a second-order reaction. In the absence of an acid catalyst, hydrogen ions are formed from the ionisation of dicarboxylic acid, and the order of the reaction is 2.5 [55]. More complicated rate equations are proposed by considering the reverse reaction, and the effect of dielectric constant of the medium on ionisation of diacid [56, 57]. 

These results and discussion in favor of the p-toluene sulfonic acid (pTSA) as an effective catalyst for polyesterification of dimer acid and butanediol strongly supports the proton-catalyzed nature of polyesterification. Usually, the proton-catalyzed mechanism for esterification is extrapolated to proton-catalyzed polyesterification [104]. The polyesterification of dimer acid and butanediol involves protonation of the dicarboxylic acid by the reaction of protonated species with the hydroxy group of glycol to yield the polyester. The proton catalyzing the protonation of carboxylic acid is provided by the carboxyl group of the monomer, i.e., dimer acid, and by pTSA in absence and presence of added catalyst, respectively. 

The extent of a reaction may alter naturally for instance, parallel reactions of a higher order do exist. In connection with consecutive-competitive reactions, in many cases, secondary reaction products that react further appear (D), such as in the case of chlorination of organic substances, where hydrogen chloride is always generated. Another example is the polyesterification of dicarboxylic acids, upon which water formation takes place. Some industrially relevant multiple reaction systems are shown in Figure 3.18. 

The principles outlined above for polyesterification reactions are equally applicable to step-growth polymerization reactions involving other types of monomer. For example, diamines and dicarboxylic acids combine together to give polyamides (nylons). Typical reactions which produce linear polymers by step-growth polymerization are given in Table 2.1 and in most cases they are basically condensation reactions. The most notable... 

It is well known that the reaction temperature for PEE and PBT synthesis is about 250-260 C, but after the reaction temperature reaches 260 C, the cyclization and degradation reactions become considerable. As the synthesis temperature increases, the degree of the polycondensation decreases and the acid group concentration increases [144]. The kinetic polyesterification model and the effect of various physico-chemical factors on the reaction of dicarboxylic acids with glycols are discussed in [134,136,156]. 

Paatero E, Narhi K, Salmi T, Still M, Nyholm P and Immonen K (1994) Kinetic model for main and side reactions in the polyesterification of dicarboxylic acids with diols, Chem Eng Sci 49 3601-3616. 

A perfect transformation of an a2 + b2b into an ab2 polycondensation was first reported by a team of DSM NV [78, 79], Bis(2hydroxypropyl)amine reacts rapidly and almost quantitatively with the amino group, so that a bis(hydroxyalkyl) carboxylic acid is formed (see Formula 10.5). The polyesterification at higher temperatures yields a poly(ester amide), which was commercialized under the trademark Hybrane. Another example of an in situ formation of an ab2 monomer was described by Shu et al. [80]. The reaction of 1,4-diaminobenzene with the monoanhydride of a diphenyl ether tetracarboxylic acid (see Formula 10.5) produces an amino dicarboxylic acid which upon further polycondensation yields a hb poly(amide imide). Polycondensations of 4,3, 5 -trifluorodiphenylsulfone with commercial diphenols were studied by the Fossum group [81, 82]. The para C-F bond id particular reactive and substitution of one meta-position lowers the reactivity of the last C-F group. Therefore, variation of the reactions conditions allows for systematic variation of the DB. 

The direct polyesterification reaction of diacids with glycols is the most important industrial synthetic route to polyester polyols. The second most important synthetic route is the transesterification reaction between dimethyl esters of dicarboxylic or dibasic acids (dimethyl adipate, dimethyl terephthalate, dimethyl carbonate or even polyethylene terephthalate) and glycols (reaction 8.2) [1, 3-8]. 

The products from the above polyesterifications are brittle materials. They are therefore modified with oils, either drying or nondrying. Such oil-modified resins bear the names of alkyds. While glycerol is widely used, other polyhydroxy compounds (polyols) are also utilized. These may be trimethylolpropane, pentaerythritol, sorbitol, or others. Phthalic anhydride is usually used in alkyd preparations. Other dicarboxylic compounds, however, may also be included for modification of properties. Common modifiers might be isophthalic, adipic, or sebacic acids, or maleic anhydride. In addition, many other acid modifiers are described in the patent literature. 

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