Commercial linear saturated polyesters

A large number of polyesters is commercially available. These polymers are conveniently classified into the following types - linear unsaturated polyesters linear saturated polyesters of low molecular weight linear saturated polyesters of high molecular weight network polyesters poly(allyl ester)s and polycarbonates. Each of these groups is considered separately in this chapter. 

The polymers making up this group of polyesters are linear saturated polyesters of molecular weight less than 10 000. Polyesters of this type find commercial application mainly as plasticizers. It may be noted that low molecular weight saturated polyesters of a different kind are also of commercial importance these are hydroxy-terminated polyesters which are used for the preparation of polyurethanes. These intermediate polymers are described in Section 14.3.2.2. 

Polyesters are the reaction product of dibasic acids with polyfunctional hydroxyl-bearing materials. Both the linear saturated polyesters and the unsaturated polyesters have achieved commercial significance. 

On the other heind, the linear unsaturated polyester resins find use in memy commercial applications, such as in producing solventless lacquers, and thermosetting molding compounds. The resin is normally prepcured by the reaction of a saturated diol with a mixture of an unsaturated dibasic acid and a modifying dibasic acid or its corresponding anhydride. It is commonly referred to as... 

The saturated polyesters that find conunercial applications are mostly linear, except for some specially prepared branched polymers used in the preparation of polyurethanes. The linear polyesters became commercially important materials early in this century and still find many uses in industry. The earliest studies reported condensations of ethylene, trimethylene, hexamethylene, and de-camethylene glycols with malonic, succinic, adipic, sebacic, and orthophthalic acids. Later studies showed that such condensations yield high molecular weight compounds. Nevertheless, these polyesters exhibit poor hydrolytic stability and are generally low-melting. Subsequently, however, it was found that aromatic dicarboxylic acids yield polymers with high melting points, and poly(ethylene terephthalate), which melts at 265 C, is now an important commercial material. 

The saturated polyesters that find commercial applications are mostly Unear except for some specially prepared branched polymers used in the preparation of polyurethanes. The linear polyesters became... 

Linear unsaturated polyesters are prepared commercially by the reaction of a saturated diol with a mixture of an unsaturated dibasic acid and a modifying dibasic acid (or corresponding anhydrides). In principle, unsaturation desired in a polyester can be derived from either an unsaturated diol or an unsaturated acid for economic reasons the latter is invariably preferred. As mentioned previously, the unsaturated acid provides sites for subsequent cross-linking the function of the modifying acid is to reduce the number of reactive unsaturated sites along the polymer and hence to reduce the cross-link intensity and brittleness of the final product. Some acids and anhydrides which are used to modify polyesters are, in fact, unsaturated but the double bonds are not sufficiently reactive to represent sites for subsequent cross-linking. 

Unsaturated polyesters are based on macromolecules with a polyester backbone in which an unsaturated acid or combination of a saturated with an unsaturated acid are condensed with a glycol. A three-dimensional structure is produced when the macromolecule is crosslinked through the unsaturation. Commercial unsaturated polyester resin formulations, neglecting consideration of additives, initiators, extenders, and fibrous reinforcing materials, consist essentially of a linear resin, a crosslinking (reactive diluent) monomer (ca. 18-40 wt. %), and inhibitors to retard crosslinking until the resin is used by the fabricator. The simplest member of the polyester series, ethylene maleate (or ethylene fumarate), is prepared as follows ... 

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