Polyesters hydrolytic stability

This dicarboxyhc ester is then copolycondensed with the other reactants in PET manufacture to produce a flame-retardant polyester [63745-01-7]. The advantage of this rather unusual phosphinate stmcture is its high thermal and hydrolytic stability. The fabric is probably used mainly for flirnishings in pubhc buildings in Japan. 

Such polyurethanes have excellent hydrolytic stability compared to water-reducible polyesters and superior abrasion resistance. In view of the importance of developing low solvent emission coatings, considerable effort is being devoted to new types of water-borne urethane resins (62,63). 

As previously mentioned, some urethanes can biodegrade easily by hydrolysis, while others are very resistant to hydrolysis. The purpose of this section is to provide some guidelines to aid the scientist in designing the desired hydrolytic stability of the urethane adhesive. For hydrolysis of a urethane to occur, water must diffuse into the bulk polymer, followed by hydrolysis of the weak link within the urethane adhesive. The two most common sites of attack are the urethane soft segment (polyol) and/or the urethane linkages. Urethanes made from PPG polyols, PTMEG, and poly(butadiene) polyols all have a backbone inherently resistant to hydrolysis. They are usually the first choice for adhesives that will be exposed to moisture. Polyester polyols and polycarbonates may be prone to hydrolytic attack, but this problem can be controlled to some degree by the proper choice of polyol. 

Due to the high reaction temperatures required during the last stages of these syntheses, side reactions cannot be avoided. Acetaldehyde, carboxyl endgroups, and vinyl endgroups are formed during PET and PEN synthesis. The formation of 2,2/-oxydiethylene moieties in polymer chains by etherification of hydroxyl endgroups is also a well-known side reaction of EG polyester syntheses.264 These reactions should be carefully controlled since they can exert an important influence on polymer properties such as Ts, mechanical properties, hydrolytic stability, and discoloration. 

Similarly, triphenylphosphine dichloride (TPPCI2) can activate aromatic carboxylic acids in pyridine through the formation of acyloxyphosphonium salts (Scheme 2.30).313 A side reaction between tire intermediate acyloxyphosphonium species and a second carboxyl endgroup leading to the formation of anhydrides has been reported.313 This chain-limiting reaction decreases tire molar mass, while the presence of anhydride linkages in tire chains adversely affects the thermal and hydrolytic stability of the final polyester. 

Polyesters are another important class of polyols. There are many polyester types used, so a generic structure is shown in Scheme 4.4. They are often based on adipic acid and either ethylene glycol (ethylene adipates) or 1,4-butanediol (butylene adipates). Polyesters, because of the polar carbonyl groups, contribute more to intermolecular forces, and physical properties such as tear and impact resistance are often improved by using them. They are also utilized for their solvent and acid resistance and light stability. Relatively poor hydrolytic stability is... 

Siloxane containing interpenetrating networks (IPN) have also been synthesized and some properties were reported 59,354 356>. However, they have not received much attention. Preparation and characterization of IPNs based on PDMS-polystyrene 354), PDMS-poly(methyl methacrylate) 354), polysiloxane-epoxy systems 355) and PDMS-polyurethane 356) were described. These materials all displayed two-phase morphologies, but only minor improvements were obtained over the physical and mechanical properties of the parent materials. This may be due to the difficulties encountered in controlling the structure and morphology of these IPN systems. Siloxane modified polyamide, polyester, polyolefin and various polyurethane based IPN materials are commercially available 59). Incorporation of siloxanes into these systems was reported to increase the hydrolytic stability, surface release, electrical properties of the base polymers and also to reduce the surface wear and friction due to the lubricating action of PDMS chains 59). 

The thermoplastic polyurethanes are available in a more limited hardness range than the styrenics, and are characterised by excellent strength and toughness, and oil resistance. Of the two major types available, polyester (TPAU) and polyether (TPEU), the latter exhibits superior hydrolytic stability and low temperature performance. 

These materials are again strong, tough and oil resistant, but are only available in a limited hardness range. Their hydrolytic stability is superior to the polyester thermoplastic polyurethanes, but they do require additional protection in applications where this could be a problem. 

The polyesters made by Carothers and his team proved a dead end in terms of commercial development for the time being, since the majority of them had melting points too low for practical utility, and there were also problems with low hydrolytic stability. Carothers turned to other classes of polymer, including, in 1934, polyamides, which he had previously briefly explored with Hill without any success. This work led to nylon fibres - first with Coffman, to nylon 9, then with Peterson, to nylon 5,10, and then, early in 1935, with Berchet, to nylon 6,6 [17],... 

Polycarbodiimides are also used as additives to provide long-term hydrolytic stability to polyester components in service in moist and humid environments (e.g. glass-filled PET in dishwasher applications). 

Completely aliphatic polyesters, made from aliphatic diacid and aliphatic diol components), are not of major industrial importance because of their low melting temperatures and poor hydrolytic stability. (Low-molecular-weight aliphatic polyesters are used as plasticizers and prepolymer reactants in the synthesis of polyurethanes see Secs. 2-12e, 2-13c-2). 

Polyesters usually have good thermal and oxidative stability (up to 200°C) but have poor hydrolytic stability at elevated temperatures. 

Uses. Neopentyl glycol is used extensively as a chemical intermediate in the manufacture of polyester resins (see Alkyd resins), polyurethane polyols (see Urethane POLYMERS), synthetic lubricants, polymeric plasticizers (qv), and other polymers. It imparts a combination of desirable properties to properly formulated esterification products, including low color, good weathering and chemical resistance, and improved thermal and hydrolytic stability. 

The weatherability and hydrolytic stability of unsaturated polyesters based on neopentyl glycol have made it a popular intermediate for use in formulations exposed to severe conditions, eg, in gel coats for cultured marble and marine applications (see Coatings, MARINE) (13). 

In addition, polyester polyols are made by the reaction of caprolactone with diols. Poly(caprolactone diols) are used in the manufacture of thermoplastic polyurethane elastomers with improved hydrolytic stability. The hydrolytic stability of the poly(caprolactone diol)-derived TPUs is comparable to TPUs based on the more expensive long-chain diol adipates. Polycthcr/polycstcr polyol hybrids arc syndicsized from low molecular weight polyester diols, which are extended with propylene oxide. 

Among the polyurethane, polyester, and polyamide thermoplastic elastomers, those with polyether-based elastomer segments have better hydrolytic stability and low temperature flexibility, whereas polyester-based analogues are tougher and have the best oil resistance (43). Polycaprolactones and aliphatic polycarbonates, two special types of polyesters, are used to produce premium-grade polyurethanes (12). 

Many papers have shown that the water absorption of a syntactic foam is proportional to that of its binder. Polyester syntactic foams, for example, absorb more water, even with dressing additives (silanes, vide infra) than do epoxy syntactic foams (Fig. 11)1. The hydrolytic stability of epoxy foams is increased when the glass microspheres are replaced by carbon ones (Table 19)40). 

The chemical structure of the prepolymer influences its chemical resistance. As a result of their structure, polyesters have inherently better oil resistance but lower hydrolytic stability. The ether groups in the polyether urethanes... 

In addition to its use in PTT, 1,3-propanediol can replace traditional glycols in urethane-based polymer systems, improving thermal and hydrolytic stability. As a partial substitute for traditional glycols in polyester systems, 1,3-propanediol can improve coating flexibility without affecting other key properties. Other applications include engine coolants and water-based inks (33). 

Polyester and polyether diols are used with MDI in the manufacture of thermoplastic polyurethane elastomers (1PU). The polyester diols are obtained from adipic acid and diols, such as ethylene glycol, 1,4-butanediol, or 1,6-hexanediol. The preferred molecular weights are 1,000 to 2,000, and low acid numbers are essential to ensure optimal hydrolytic stability. Also, caprolactone-derived diols and polycarbonate diols are used. Polyether diols are... 

The polysulfones are made by condensation polymerization of the potassium salt of bisphenol-A with dichlorodiphenyl sulfone, as discussed by S. R. Schulze and A. L. Baron. The polysulfonates are made from bisphenol-A and disulfonyl chlorides. They are more brittle than poly-sulfone and have been suggested by R. J. Schlott and co-workers to be used in coplymers with linear polyesters to improve the hydrolytic stability of the latter. 

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