Polyester diol structures

Polyesters are hydrolytically labile and offer excellent mechanical properties compared to the other commonly used polyols for biomedical applications. Table 1.1 provides a list of common polyester diol structures used in resorbable polyurethanes. Although polyester urethanes were generally considered unsuitable for biostable... 

Table 1.1 List of common polyester diol structures used in resorbable polyurethanes...

These improved properties may be related to 1) increased hydrogen bonding due to the increased polyester diol content, 2) increased hard segment content, and 3) evidence of crystallinity in the hard segment domain. All effects result in a higher modulus material. The structure-property relationships of these formulations in terms of their crystalline morphology are discussed in another paper. ... 

By using the raw materials presented diols, triols and dicarboxylic acids, it is possible to obtain a large variety of polyester polyol structures. For example to use one type of glycol and one type of dicarboxylic acid, but many other combinations are possible, such as using one dicarboxylic acid and two types of glycol or to use a glycol together with a small quantity of triol, to obtain a branched polyester polyol. 

Chapter 12.5). Polyester polyols in reality, have the theoretical functionality, which is a great advantage for many polyurethane applications. For polyester diols the functionality is 2 OH groups/mol. This structural aspect results in the polyester diols giving PU elastomers with excellent physico-mechanical properties, superior to all polypropylene glycols obtained by anionic PO polymerisation. 

Lights stability of polyurethanes depends to a large extent on their chemical structure, and both components (Le., isocyanate and polyol) have an influence. Polyurethanes based on aliphatic isocyanates and polyester diols show the best light stability if yellowing is considered, whereas polyurethanes based on aromatic isocyanates and polyether diols are worst in this respect. 

Cadiz and co-workers [46] prepared telechelic polyester diols through two subsequent thiol-ene reactions. That is, a step growth polymerisation using allyl-lO-undecenoate and 3,6-dioxa-l,8-octanedithiol, followed by end-group post-polymerisation modification with 2-mercaptoethanol. Telechelics based on divinyl monomers are interesting materials with potential applications in the tailoring of polymer structures and properties. 

Structopendant unsaturated polyesters, containing double bonds within the polymer chain, are produced by step-growth polycondensation reaction of an unsaturated diacid or anhydride, such as fumaric add or maleic anhydride, with a diol. Structural unsymmetry in the diol component lowers the viscosity of the prepolymer. Mostly, crosslinking of the structopendant unsaturated polyester is accomplished by copolymerization with alkene monomers such as styrene, methyl methacrylate, or others using radical initiators. 

Polymerisation of a diol with a dicarboxybe acid is exemplified by the production of a polyester from ethylene glycol and terephthabc 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 resibency its structure is probably ... 

Depending on dieir structure, properties, and syndietic methods, degradable polyesters can be divided into four groups poly(a-esters), poly(fi-esters), poly(lactones), and polyesters of aliphatic diols and diacids. 

Figure 25.3 b) shows a generic polyester-based polyurethane. The most common polyester repeat units are derived from the polycondensation of adipic acid and a diol, such as ethylene glycol, which results in the structure shown in Fig, 25.4. The average molecular weight of the polyester sequences between urethane links commonly ranges between 400 and 6,000 g/mol. 

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