Industrial polyesterifications

Organic titanates perform three important functions for a variety of industrial applications. These are (/) catalysis, especially polyesterification and olefin polymerization (2) polymer cross-linking to enhance performance properties and (3) Surface modification for adhesion, lubricity, or pigment dispersion. 

The aromatic polyesters such as poly(ethylene terephthalate) (PET) were commercialized from about 1946 as fibres, but, because of the high processing temperatures, it was only some 20 years later that they appeared as engineering thermoplastics. The dominance of PET in beverage containers ensures the importance of the synthesis, processing and recycling of PET. Polyesterification is a suitable stepwise reaction to illustrate the principles of this industrially important polymerization. Applications in reactive processing will then be considered. 

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]. 

Uses Esteritication/transesteritication/polyesterification catalyst for prep, of esters, polyesters, alkyds, methacrylate esters 100 C, in coatings industry tor prep, of alkyd resins, and in reactions for curing blocked isocyanate... 

PET and PBT can be eonveniently synthesized, both at laboratory and industrial scale, in the presenee of metal eatalysts in a two-step-polyesterification of the diols, ethylene glycol or 1,4-butanediol respectively, and dimethyl terephthalate (DMT) or terephthalic acid (TPA). The first step is basically a transesterification or esterification process depending on the use of DMT or TPA respectively, while the second step is the polycondensation of the resulting oligomers. The polycondensation step occurs at higher temperature and at reduced pressure to facilitate the distillation of the diols and consequently the polymerisation of the oligomers. 

The Pechini method refers to an original process developed by Pechini (95) for the preparation of titanates and niobates for the capacitor industry. The method has since been applied to many complex oxide compositions (96,97). Metal ions from starting materials such as carbonates, nitrates, and alkoxides are complexed in an aqueous solution with a-carboxylic acids such as citric acid. When heated with a polyhydroxy alcohol, such as ethylene glycol, polyesterification occurs, and on removal of the excess liquid, a transparent resin is formed. The resin is then heated to decompose the organic constituents, ground, and calcined to produce the powder. The typical steps in the method are illustrated in Figure 2.34 for the preparation of SrTiOs powders (98). 

PBT can generally be produced by reacting 1,4-butanediol with an aromatic diester - dimethyl terephthalate (DMT) or diacid -terephthalic acid (TEA), in the presence of a polyesterification catalyst. Methanol is the major byproduct in the former route, while the water is the major byproduct in the latter route. Although polycondensation to high conversions implicitly requires stoichiometric balance of reacting groups, industrial processes for manufacturing polyesters such as PBT involve initial use of excess BD, which is later removed and recycled in the process. At the time when Pilati published his review [18], most publications described the trans-esterification between BD and DMT. Since that time, the majority of patents have been related to the direct polyesterification of BD by TEA [23-28]. 

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. 

FIGURE 3.18 Sample multiple reaction systems that are industrially relevant polyesterification of unsaturated carboxylic acids and alkali fusion. 

---