Polyester-Based Polyurethanes

Fatty acids, both saturated and unsaturated, have found a variety of applications. Brassilic acid (1,11-un-decanedicarboxylic acid [BA]), an important monomer used in many polymer applications, is prepared from erucic acid (Scheme 2), obtained from rapeseed and crambe abyssinica oils by ozonolysis and oxidative cleavage [127]. For example, an oligomer of BA with 1,3-butane diol-lauric acid system is an effective plasticizer for polyvinylchloride. Polyester-based polyurethane elastomers are prepared from BA by condensing with ethylene glycol-propylene glycol. Polyamides based on BA are known to impart moisture resistance. 

Abrasion-resistant duties may involve abrasion in an aqueous phase or abrasion by dry particulate materials. The selection of the polyurethane type is most important to obtain the best results. Polyester-based polyurethanes perform best in dry abrasion due to their low hysteresis properties and excellent resistance to cut initiation and propagation. However, polyester polyurethanes are susceptible to hydrolytic degradation, and therefore polyether polyurethanes are normally used for aqueous abrasion duties. 

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. 

Several polymer-related uses of brassylic acid (BA) have been investigated. For example, a BA/l,3-butanediol/lauric acid oligomer is an effective plasticizer for poljrvinyl chloride,[6] BA/ethylene glycol and BA/propylene glycol polymers function as polyester based polyurethane elastomers,[7] and BA has been patented as a cross-linker for glycidyl methacrylate copolymer powder coatings.[8] However, the most detailed studies have involved polyamides selected data from these studies are summarized in Table I. 

El Shahawi, M.S., Kiwan. A.M., Al-Daheri. S.M.. Saleh, M.H., The retention behavior and separation of some soluble organophosphate insecticides on polyester-based polyurethane foams. Talanta (42) 1995. 1471-1478. 

The temperature also plays a large part in the speed of the hydrolysis. Polyethers are also more resistant to hydrolysis than polyester-based polyurethanes. 

Hydrolysis temperature. The effect experienced particularly by polyester-based polyurethanes, where prolonged contact with water or water-based liquids causes breakdown and failure of the polyurethane. 

Chemigum Polyester-based polyurethane (elastomer) Goodyear... 

In the aromatic series, carbodiimides having a substituent in the o-position are preferred. Examples include N,N -di-t)-tolylcarbodiimide and NJ l -di-2,6-diethylcarbodiimide, the latter being a useful stabilizer for polyester based polyurethanes. ... 

Oligomeric carbodiimides are efficient stabilizers for polyester, polyester based polyurethanes, polyether based polyurethanes and polyether based poly(urethane ureas). Oligomeric carbodiimides are commercially available under the trade name Stabaxol from Rhein Chemie, a subsidiary of Bayer. 

The polymer lifetime of polyester based polyurethanes with 3 % of monomeric carbodiimide added is increased ten fold at 35... 

Covers three types of tricot knit nylon cloth laminated to a polyester-base polyurethane foam and impregnated with an activated-carbon mixture. 

This paper presents results from aging polyester based polyurethanes In methanol and water environments and In other mixtures of these media. The Influence of aging on mechanical properties was assessed by measuring tensile strengths and elongations at... 

In addition, polymer B Is reported to provide superior resistance to hydrolytic attack compared to other polyester based polyurethanes. 

The superior characteristics of polyester polyol based polyurethanes are explained by a better crystalline structure [1, 7] in the urethane segment, compared to the majority of poly ether polyols which are amorphous [except polytetrahydrofuran (PTHF)], due to the superior secondary forces between the polyester chains [8] and also due to a superior thermal and fire resistance, compared to polyether polyol based polyurethanes. Polyester-based polyurethanes (flexible foams, coatings), have a superior solvent resistance compared to the polyether-based polyurethanes [8]. 

Polyester polyols have an intrinsic defect they are liable to hydrolyse under high humidity/temperature conditions. To prevent the hydrolysis of polyester-based polyurethanes a worldwide research effort, led to the synthesis of polyester polyols with improved hydrolysis resistance [1, 6-8, 12, 13]. 

The composition and structure of the polyester polyols lead to polyurethanes with distinct properties. These polyester-based polyurethanes have specific applications, as shown in Table 8.5. 

Polyurethanes. Polyester base polyurethanes were reported to support fungal growth better than polyether base polyurethanes (15). Polyurethanes derived from cellulose hydrolysates were degraded by cellusin... 

The more viscous, mastic-type cements include some of the epoxies, urethanes and sflicones. Epoxies adhere well to both thermosets and thermoplastics. But epoxies are not recommended for most polyolefin bonding. Urethane adhesives have made inroads into flexible packaging, the shoe industry, and vinyl bonding. Polyester-based polyurethanes are often preferred over polyether systems because of their higher cohesive and adhesive properties. Sflicones are especially recommended where both bonding and sealing are desired. 

Polyurethane ether (PUR-ether) foams are thought to degrade primarily by oxidation, particularly in the presence of light, resulting in discolouration and a loss of mechanical properties. Polyurethanes synthesized from a polyether polyol and an aromatic diisocyanate such as diphenylmethane diisocyanate (MDI) are highly vulnerable to photo-oxidation, whereas polyester-based polyurethanes are more resistant to ultraviolet radiation (Kerr and Batcheller, 1993). Metal ions, particularly copper, aluminium and zinc, form chelates with some polyurethanes imparting increased sensitivity to photo-oxidation (Ranby and Rabek, 1975). 

The chemical resistance of many TPEs is poor compared to that of conventional mbbers. Polyurethanes, copolyesters, and copolyamldes are very susceptible to oxidation, especially at elevated temperatures. Antioxidants and other additives are added to commercial products to improve the chemical resistance of these materials. Carbon black can be added to improve stability to UV light if the color of the material is unimportant. Hydrolytic stability is poor for the polyester-based polyurethanes and the copolyamldes because the ester linkage can be attacked by water. For all TPEs, certain organic solvents can degrade these materials if one or both of the blocks will dissolve in the particular solvent. The resistance to many common oils and greases is high for the more polar TPEs. 

Segmented polyurethane elastomers, prepared from diisocyanates, macrodiols and chain extenders, are frequently used in the construction of implantable medical devices, such as cardiac pacemakers, heart valves, catheters, and heart assist devices, because of their excellent mechanical properties and haemocompatibility. Polyether macrodiols, such as poly(tetramethylene oxide) (PTMO), are used to prepare polyurethanes for implant, since they offer an increased resistance to enzymatic hydrolysis compared with polyester-based polyurethanes. 

To study both polyether- and polyester-based polyurethane systems. 

Texin 5370 is a blend of polyester-based polyurethane and polycarbonate. It offers high impact strength and high stiffness. Steam sterilization or boiling should be avoided (Tables 4.3, 4.12, and 4.13). 

Evans, D.M. and I. Levisohn, Biodeterioration of polyester-based polyurethane. International Biodeterioration Bulletin, 4(2) 89-92,1968. 

Fig. 11.3. Typical infrared spectrum of a polyester based polyurethane.

Aft r a low productive decade, the Mobay Corp. was formed by Bayer and Monsanto for the production of polyurethanes in the U.S. in 1953. However, the first polyester-based polyurethane foam disintegrated in humid air and could not compete with rubber latex foam. This difficulty was overcome by the use of hydroxyl terminated polyethers instead of polyesters. 

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