Polyesters from Diols and Dicarboxylic Acids

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. 

Preparation of a Low-Molecular-Weight Branched Polyester from a Diol, a Triol and a Dicarboxylic Acid by Melt Condensation 

Safety precautions Before this experiment is carried out, Sect. 2.2.5. must be read as well as the material safety data sheets (MSDS) for all chemicals and products used. 

1-2 g of the polyester are dissolved by warming with 50 ml of acetmie and, after cooling, are titrated as quickly as possible with 0.1 M alcoholic potassium 

To acetylate the free hydroxy groups of a polyester, a solution of 15 g of freshly distilled acetic anhydride (bp 140°C) in 35 g of freshly distilled dry pyridine is prepared. The solution, which turns slightly yellow with time, is stored in a dark bottle. 

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Polyesters from diols and dicarboxylic acids (polyester fibres). 

Polyesters from Diols and Dicarboxylic Acid Derivatives... 

There has in the past been some confusion in the use of the term alkyd, which is said to have been derived from alcohol plus acid. The definition offered by Kienle [1], discussed later, is broad enough to include all polyesters derived essentially from diols and dicarboxylic acids, and consequently linear polyesters were initially included in this class of polymer. On the other hand, Bjorksten et al. [2], in their 1956 compilation of published information about polyesters, restrict the term polyester to the polycondensation products of dicarboxylic acids with dihydroxy alcohols, and say that this definition does not include materials commonly known as alkyds . At the present time, there are still problems of nomenclature in the fibre field arising from the use of polyester as a generic term to cover fibres containing only a very restricted range of chemical groups. 

In the early days of macromolecular chemistry, synthetic polymers were simply labeled according to the monomer from which they were prepared. Thus, ethylene polymers became poly(ethylenes), styrene polymers became poly(styrenes), and those from lactams became poly (lactams). In other cases, the choice of name was provided by a characteristic group occurring in the final polymer. Thus, polymers from diamines and dicarboxylic acids were called polyamides, and those from diols and dicarboxylic acids were called polyesters. This phenomenological nomenclature fails, of necessity, when more than one kind of monomeric unit can be formed from a given monomer. 

Wick, G. and Zeitler, H., Cyclic oligomers in polyesters from diols and aromatic dicarboxylic acids, Angew. Makromol. Chem., 112, 59 (1983). 

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. 

Aliphatic thermoplastic polyesters represent a class of materials that is attracting a considerable amount of attention because they are i) biodegradable and biocompatible and ii) increasingly accessible from the exploitation of diols and dicarboxylic acids derived from renewable resources. If long methylene chains are present in the monomers, the ensuing products resemble polyethylene (PE) in strnctnre and, hence, in most properties, have the added advantage of biodegradability. 

Several review articles on biodegradable polymers and polyesters have appeared in the literature [12-22]. Extensive studies have been carried out by Al-bertsson and coworkers developing biodegradable polymers such as polyesters, polyanhydrides, polycarbonates, etc., and relating the structure and properties of aliphatic polyesters prepared by ROP and polycondensation techniques. In the present paper, the current status of aliphatic polyesters and copolyesters (block, random, and star-shaped), their synthesis and characterization, properties, degradation, and applications are described. Emphasis is placed primarily on aliphatic polyesters derived by condensation of diols with dicarboxylic acids (or their derivatives) or by the ROP of cyclic monoesters. Polyesters derived from cyclic diesters or microbial polyesters are beyond the scope of this review. 

Just as simple esters and amides can be made by condensation reactions, polyesters such as Dacron and Mylar are made by reacting diols with dicarboxylic acids (Figure 13.15 A). Similarly, polyamides such as nylon form from amines and carboxylic acids. Starting from anhydrides and amines, polyimides can be formed. These structures tend to be extremely stable, and so are valuable in high temperature applications. 

The aromatic polyesters were prepared by melt condensation from aromatic dicarboxylic acids, the diacetates or dipropionates of aromatic diols, and acetoxybenzoic acids. Specific preparations for the different types of polyesters are given in the references, especially references 5, 11, and 20. 

Aliphatic polyesters derived from the polycondensation of diols with aliphatic dicarboxylic acids are another important class of synthetic biodegradable polymers. Since 1994, Showa Highpolymer in Japan has been producing a family of aliphatic polyesters known as Bionolle , obtained from butanediol and succinic acid to give polybutylene succinate (PBS), and the copolymer polybutylene succinate adipate (PBSA) obtained from butanediol, succinic acid and adipic acid. Polyethylene succinate (PES) was also produced. 

More recently we have shown Aat oligomeric polyesters form in aqueous oil-in-water (o/w) emulsion from molten mixtures dicarboxylic acids and diols below 100°C (14,15). In this case the emulsion particles served as a hydrophobic phase and catalysts were surface-active sulfonic acids. The method was restricted, however, to water-insoluble monomers that were liquid at the polymerization tenq)erature. 

Trinitrochlorobenzene (piciyl chloride) in pyridine-A -mcthylpyrrolidi-none (NMP) solutions were later used for the preparation of polyesters from dicarboxylic acids and diphenols or aliphatic diols,309 but better results have been obtained with sulfonyl chlorides and phosphorus compounds. 

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. 

A novel chemoenzymatic route to polyester polyurethanes was developed without employing highly toxic isocyanate intermediates. First, diurethane diols were prepared from cyclic carbonates and primary diamines, which were subsequently polymerized with dicarboxylic acids and glycols by using lipase CA as catalyst, yielding the polyurethanes under mild reaction conditions. 

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 ... 

Propanediol. Both the diol and the dicarboxylic acid components of poly-trimethylene-terephthalate, a high performance polyester fiber with extensive applications in textile apparel and carpeting, are currently manufactured from petrochemical raw materials. 

The formation of polyesters from a dialcohol (diol) and a dicarboxylic acid (diacid) is used to illustrate the stepwise kinetic process. Polymer formation begins with one diol molecule reacting with one diacid, forming one repeat unit of the eventual polyester (structure 4.3) ... 

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