Polyesters cyclic anhydrides

Polyesters have been obtained in organic medium by polyesterification of hydroxy acids,328,329 hydroxy esters,330 stoichiometric mixtures of diols and diacids,331-333 diols and diesters,334-339 and diols and cyclic anhydrides.340 Lipases have also been reported to catalyze ester-ester interchanges in solution or in die bulk at moderate temperature.341 Since lipases obviously catalyze the reverse reaction (i.e., hydrolysis or alcoholysis of polyester), lipase-catalyzed polyesterifications can be regarded as equilibrium polycondensations taking place in mild conditions (Scheme 2.35). 

Lipase-catalyzed synthesis of polyesters from cyclic anhydrides and oxi-ranes was reported. The polymerization took place by PPL catalyst and the molecular weight reached 1 x 10" under the selected reaction conditions. During the polymerizahon, the enzymatically formed acid group from the anhydride may open the oxirane ring to give a glycol, which is then reacted with the anhydride or acid by lipase catalysis, yielding the polyesters. 

Coreactants, in microencapsulation, 16 444 Coreactive curing agents, 10 388-389, 392-411, 418. See also Curing agents amine functional, 10 392 401 carboxylic functional polyester and anhydride, 10 401—406 cyanate ester, 10 411 cyclic amidine, 10 410 isocyanate, 10 410 melamine-, urea-, and phenol-formaldehyde resins,... 

When the cyclic anhydride is maleic anhydride, the product understandably becomes an unsaturated polyether ester somewhat similar to traditional unsaturated polyester resins (UPRs). 

Maleic anhydride is a cyclic anhydride with one double bond in the ring and two double-bonded oxygens hanging off the ring. The resulting reactivity leads to maleics use in making polymers, unsaturated polyesters, alkyd resins, plasticizers, and dicarboxylic acids. 

It is apparent that the mode of reaction of the hyperbranched polyesteramides must be distinctively different from those of the known commercial crosslinkers. In order to explain these results, the hyperbranched polyesteramides should in our view not be regarded as simply multifunctional polymeric crosslinkers but rather as precondensed forms of two-functional crosslinkers (the addition product of diisopropanolamine and the cyclic anhydride), as depicted in Fig. 22, left. Bearing in mind the chemical fate of benzoic acid (2.2.1, Fig. 11) which was condensed with a polyesteramide resin and which appeared to transesterify at least as fast as it esterified, the mode of reaction of polyesters comprising aromatic acid end groups must be in accordance and comprised of both transesterification and esterification. 

Epoxides readily undergo anionic copolymerization with lactones and cyclic anhydrides because the propagating centers are similar—alkoxide and carboxylate [Aida et al., 1985 Cherdron and Ohse, 1966 Inoue and Aida, 1989 Luston and Vass, 1984]. Most of the polymerizations show alternating behavior, with the formation of polyester, but the mechanism for alternation is unclear. There are few reports of cationic copolymerizations of lactones and cyclic ethers other than the copolymerizations of [5-propiolactone with tetrahydrofuran and... 

This article summarizes and analyzes the results obtained for the anionic copolymerization of cyclic ethers with cyclic anhydrides. This reaction is of great practical importance, especially as curing reaction of epoxy resins and is also used for the preparation of linear polyesters with special functional pendant groups. 

In this paper, we try to review results obtained from anionic copolymerization of cyclic ethers with cyclic anhydrides. For a better understanding data and theoretical views on non-catalyzed copolymerizations are also included. We concentrate mainly on the kinetics and mechanism of copolymerization and the effect of the type and character of the initiator used. The influence of the epoxide and anhydride structure on copolymerization, of proton donors on the rate and course of copolymerization, and on the molecular weight of the resulting polyesters are also discussed. 

Data on molecular weights of polyesters can provide information on the mechanism and termination and transfer reactions. As follows from section 3.2.3 the copolymerization of epoxides with cyclic anhydrides should proceed stoichiometrically without transfer or termination reactions, and the average degrees of copolymerization should only depend on the molar ratio of monomers to the initiator. Polymers with a narrow molecular Weight distribution should be obtained. 

Cyclic anhydrides are diacids with one molecule of water eliminated from the condensation of the two acid groups. They can be useful for the synthesis of polyesters. The reaction proceeds in two steps because the free acid formed in the first step (Eq. 2.7) is much less reactive than the original anhydride ... 

Conventional ring-opening polymerization of cyclic anhydrides, carbonates, lactones, and lactides require extremely pure monomers and anhydrous conditions as well as metallic catalysts, which must be completely removed before use, particularly for medical applications. To avoid these difficult restrictions, an enzymatic polymerization may be one of the more feasible methods to obtain the polyesters. This method was first reported by two independent groups (Kobayashi [152] and Gutman [153]) who showed that lipases, enzymes capable of catalyzing the hydrolysis of fatty acid esters, can polymerize various medium-sized lactones. 

An equimolar mixture of epoxide and cyclic anhydride has the stoichiometry of a polyester. Fisher47 has shown that if a tertiary amine is added to such a mixture, maintained at 70-100 °C, epoxide and anhydride disappear at identical rates to yield polyester. This relationship held even if the epoxide was present in excess. The excess could be removed at the end of the polymerization and functioned purely as solvent. 

Alternating copolymerization is possible in other systems because new, more stable chemical bonds are formed. Copolymerization of cyclic anhydride and THF (above Tc) to a polyester may serve as an example 89) ... 

Inspection of the formulas of an epoxide and cyclic anhydride side by side reveals that an equimolecular mixture has the elemental composition of a polyester. Only a catalyst is needed to isomerize, in effect, such a mixture to a linear polyester. In such a plymerization, both epoxide and anhydride must be strictly bifunctional toward each other. Careful studies of the uncatalyzed reaction have been made by Fisch and Hoffman [80,81], who showed that some epoxide homopolymerization occurs. This gives systems in which the anhydride is only 0.5 to 0.85 mol per mol of epoxide. 

Hydroxyl and amino groups react rapidly with anhydrides, forming esters or amides, respectively, with release of an acid. Cyclic anhydrides react similarly, yielding ester- or amide-acids. Accordingly, dicyclic anhydrides can couple two compounds and were, therefore, studied as chain extenders, particularly for polyesters. Some examples of commercially available dicyclic anhydrides are given in Figure 6. Pyromellitic dianhydride (PMDA, 1) is probably the most important member of this group. 

Maleic anhydride copolymers comprise a number of cyclic anhydrides and are used as well. However, these compounds will give branched or even cross-linked polyesters, due to the high functionality, and are outside the scope of this chapter. 

A cyclic anhydride, such as phthalic anhydride or maleic anhydride, will form a nearly 1 1 alternating copolymer with alkylene oxides. This reaction is the same one used in the curing (hardening) of epoxy resins. A large number of initiators can be used for this reaction, including tertiary-amines, various Lewis acids, and bases including alkoxides. The uncatalyzed reaction invokes initiation with a hydroxyl group (125,126). This reaction can be used to introduce a polyester unit into a polyether polymer chain. With phthalic anhydride, the reaction proceeds as follows ... 

The cyclic carbonate can then be copolymerized with cyclic anhydride to yield, with loss of carbon dioxide, a polyester of relatively high molecular weight. This copolymerization is initiated by a number of inorganic salts including sodium cyanide and potassium chloride, bases such as potassium hydroxide or sodium amide, and Lewis acids at 200°C. Presumably, the initiation begins with nucleophilic attack of an anion on the cyclic carbonate... 

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