Polyester Syntheses

The preceding discussions of the kinetics and molecular weight distributions in the step-growth polymerization of AB monomers are clearly exemplified by the esterification reactions of such monomers as glycolic acid or co-hydroxydecanoic acid. Therefore one method for polyester synthesis is the following ... 

Chemical Properties. The chemistry of 1,4-cyclohexanedimethanol is characteristic of general glycol reactions however, its two primary hydroxyl groups give very rapid reaction rates, especially in polyester synthesis. 

The synthesis and properties of polyesters have been treated in numerous encyclopedia and general review articles.1-9 This chapter, therefore, does not discuss these aspects extensively but focuses more on recent academic and industrial research developments in polyesters and on the practical aspects of polyester synthesis. 

Polyester chemistry is the same as studied by Carothers long ago, but polyester synthesis is still a very active field. New polymers have been very recently or will be soon commercially introduced PTT for fiber applications poly(ethylene naph-thalate) (PEN) for packaging and fiber applications and poly(lactic acid) (PLA), a biopolymer synthesized from renewable resources (corn syrup) introduced by Dow-Cargill for large-scale applications in textile industry and solid-state molding resins. Polyesters with unusual hyperbranched architecture also recently appeared and are claimed to find applications as crosstinkers, surfactants, or processing additives. 

The carboxy-hydroxy reaction (direct esterification) is the most straightforward method of polyester synthesis. It was first reported in the 1930s by Carothers10 12 and is still a very widely used method for the synthesis of polyesters from diacids and diols (Scheme 2.12) or from hydroxy acids (Scheme 2.13). Direct... 

The reaction between acid anhydrides and diols is another convenient method of polyester synthesis. The reaction proceeds in two steps with the formation of an intermediate hydroxy acid (Scheme 2.15). 

The use of silylated monomers is an interesting alternative method of aromatic polyester synthesis since the silylated gaseous by-products cannot participate in the reverse reaction, shifting polyesterification toward polymer formation. Reactions between silyl esters and acetates (Scheme 2.23) and reactions between silyl ethers and acid chlorides (Scheme 2.24) have been applied to the synthesis of linear265-267 and hyperbranched wholly aromatic polyesters202,268 269 (see Section 2.4.5.2.2). 

The reaction between acid chlorides and aliphatic alcohols or phenolic compounds commonly takes place at low to moderate temperature (—10 to 100°C) in solution or by interfacial or dispersion polymerization techniques. It has been widely applied to polyester synthesis. Reviews and books are available on the polymerization techniques as well as on the chemistry of this reaction.2,207 294... 

Ethane linkages, 407 Ethene linkages, 407 Ethylene adipates, 212 Ethylene-CO copolymer, 460 Ethylene copolymers, 446 Ethylene glycol (EG), 13, 64. See also EG polyester synthesis depolymerization with, 559 repolymerization of, 561-562 Ethylene oxide (EO) polyols, 211... 

Hyperbranched aromatic polyesters, synthesis of, 116-118 Hyperbranched aromatic polymers, 286 Hyperbranched polyamine, synthesis of, 519-520... 

Brich, Z., Nimmerfall, F., Kissel, T., and Bantle, S., Branched ter-polyesters Synthesis, characterization, in vitro and in vivo degradation behaviors, Proc. Int. Symp. Control. Rel. Bioact. Mater., 15, 95, 1988. 

Lipase-catalyzed reaction is useful for polyester synthesis and IE was employed successfully as solvent. Uyama and Kobayashi demonstrated an efficient polyester synthesis lipase-catalyzed esterification of agipic acid with butan-1,4-diol proceeded smoothly in [bmim][BF4] solvent, particularly under reduced pressure conditions (Fig. 8). Further Russel " and Nara independently reported efficient examples of the lipase-catalyzed polyester synthesis in an IE solvent system. 

Figure 8 Lipase-catalyzed polyester synthesis using IL solvent system.

In polyester synthesis via ring-opening polymerizations, metal catalysts are often used. For medical applications of polyesters, however, there has been concern about harmful effects of the metallic residues. Enzymatic synthesis of a metal-free polyester was demonstrated by the polymerization of l,4-dioxan-2-one using Candida antarctica lipase (lipase CA). Under appropriate reaction conditions, the high molecular weight polymer (molecular weight = 4.1 x 10" ) was obtained. 

Polyester synthesis was carried out hy insertion-dehydration of glycols into polyanhydrides using lipase CA as catalyst (Scheme 6). The insertion of 1,8-octanediol into poly(azelaic anhydride) took place at 30-60°C to give the corresponding polyester with molecular weight of several thousands. Effects of the reaction parameters on the polymer yield and molecular weight were systematically investigated. The dehydration reachon also proceeded in water. The reaction behaviors depended on the monomer structure and reaction media. 

If the polyester synthesis is performed with equimolar amounts of diol and diacid, then, in addition to hydroxy, carboxy-terminated oligomers, dihydroxy- and dicarboxy-terminated oligomers are formed, as shown below. In a thermodynamic equilibrium, the molar ratios of the three functionality fractions should be 2 1 1, respectively. 

Synthesis of PHA in plants is a relatively young field of study. Consequently, there remains a number of areas which have been poorly worked on and for which there are more questions than answers. Nevertheless, recent studies have shown that the usefulness of PHA in plants can reach beyond the biotechnology of polyester synthesis in agricultural crops to include PHA synthesis as a novel tool in the study of basic plant biochemical pathways and metabolism. 

The future direction of polyester R D efforts is likely to involve further progress in polyester synthesis given the wide range of potential monomer combinations, new blending technology and the use of advanced functional additives such as nanoclay reinforcements, reactive impact modifiers, anti-hydrolysis agents and chain extenders. 

Kricheldorf, H. R., Rabenstein, M., Maskos, M. and Schmidt, M., Macrocycles 15. The role of cyclization in kinetically controlled polycondensations. 1. Polyester synthesis, Macromolecules, 34, 713 (2001). 

The understanding of the SSP process is based on the mechanism of polyester synthesis. Polycondensation in the molten (melt) state (MPPC) is a chemical equilibrium reaction governed by classical kinetic and thermodynamic parameters. Rapid removal of volatile side products as well as the influence of temperature, time and catalysts are of essential importance. In the later stages of polycondensation, the increase in the degree of polymerization (DP) is restricted by the diffusion of volatile reaction products. Additionally, competing reactions such as inter- and intramolecular esterification and transesterification put a limit to the DP (Figure 5.1). 

It offers a polyester synthesis without stoichiometry to consider or condensation water to remove. In other words, an unsaturated polyester of any degree of unsaturation up to complete ether consumption can be achieved by simply adjusting the feed of maleic anhydride. 

In this procedure, the diol to be used in the synthesis of the polyester is used as the inert diluent in the synthesis step of the bis-carbamate. This avoids the requirement to use a solvent that then has to be removed prior to the polyester synthesis. The 1,4-butanediol is then incorporated into the polyester in the second stage of the reaction. 

Berkane, C. Mezoul, G. Lalot, T. Brigodiot, M. Lipase-catalyzed polyester synthesis in organic medium. Study of ring-chain equilibrium. Macromolecules 1997, 30, 7729-7734. 

Kim D-Y, Dordick JS (2001) Combinatorial array-based enzymatic polyester synthesis. Biotechnol Bioeng 76 200-206... 

M]0 = 5 M. A concentration of 5 M is fairly typical of a step polymerization that is often carried out with only the reactant(s) present (without solvent). The lowering of [H20] to achieve a particular Xn is less the more favorable the equilibrium (that is, the larger the K value). Thus the synthesis of polyamides (with typical K values > 102) is clearly easier from the equilibrium viewpoint than polyester synthesis (K 0.1-1). Polyesterification requires a greater lowering of [H20] than does polyamidation. It should be understood that simply to lower [H20] as much as possible is not the desired approach. One needs to control the [H20] so as to obtain the desired degree of polymerization. 

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