Polyethers hydrolytic stability

From their structures, it appears that the hydrolytic stability of macrocyclic lactones must necessarily be inferior to macrocyclic polyethers. Ease of synthesis of the cyclic esters is therefore one of the aspects which commend them to interest. It is probably for this reason that such lactones have not been made more often by the interesting approach of Kdgel and Schroder . These workers report the ozonolysis of dibenzo-18-crown-6 in a mixture of methanol and dichloromethane at —20°. Reduction of the ozon-ide at —75° using dimethylsulfide followed by warming and addition of acetone led to formation of 6 in 14% yield. The bis-oxalate had mp 164—165° from acetone, very similar to that of the starting crown. The transformation is illustrated below in Eq. (5.9). 

The polyether imides show much better hydrolytic stability with little change in tensile strength after exposure to water at 100°C for 1 year. These materials also show exceptional resistance to mineral acids, and are unharmed by most hydrocarbons including gasoline (petrol) and oils. 

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. 

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). 

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, 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 (22). The hydrolytic stability of the poly(caprolactone diol)-derived TPUs is comparable to TPUs based on the more expensive long-chain diol adipates (23). Polyether/polyester polyol hybrids are synthesized from low molecular weight polyester diols, which are extended with propylene oxide. 

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... 

Polyether-urethane 200 Better hydrolytic stability and resistance to fungal ... 

Polyurethane liner pads employed in naval missile launch systems are exposed to high humidities during storage and occasionally to sea water after their installation. In order to determine their durability towards water, a detailed study was made of their hydrolytic stability. Even though both polyether and polyester based urethanes can give the physical properties required for this application, only the polyether urethanes were studied since they display much superior resistance to hydrolysis (1, 2, 3, ). 

Accelerated hydrolytic stability tests Indicate that the polyether-based urethane employed In this study In the preparation of the liner pads can successfully withstand contlntious Immersion In water at 3S C for 24 years. Under such an exposure, the pads are expected to lose approximately 20 percent of their original compressive strength. 

The hydroxyl terminated polybutadienes lead to PU with physico-mechanical properties significantly lower than those of PU based on polyether or polyester polyols. The nonpolar polymeric chain and the extraordinary hydrophobicity mean that hydroxy terminated polybutadienes are used for special applications, due to their excellent electrical insulation properties which are equal or superior to epoxies or silicone elastomer systems. The hydrolytic stability of PU elastomers derived from hydroxyl terminated polybutadiene is superior to the majority of other types of PU. Thus, some specific applications of... 

Both polymers have excellent hydrolytic stability—one because it is a polyether and the other because it sterically hinders hydrolytic action. The polycarbonate, like the polyether, is reported to be compatible with polystyrene. The high T would suggest dimensional stability and utility at very high temperatures, but thermal-oxidative limitations will probably favor blend applications at moderately high continuous-use temperatures. 

As with other block copolymers, the nature of the soft segments determines the elastic behavior and low-temperature performance. TPUs based on polyester soft blocks have excellent resistance to nonpolar fluids and high tear strength and abrasion resistance. Those based on polyether soft blocks have excellent resistance (low heat buildup, or hysteresis), thermal stability, and hydrolytic stability. 

Uses Soft segment in formation of elastomers such as thermoplastic urethanes, polyether esters, polyether amides, coatings, adhesives and sealants, casting resins, and urethane foams Features Produces elastomeric end-prods, with hydrolytic stability, resist. to microbial attack, low temp, flexibility and elasticity Properties APHA 40 max. wax-like solid sol. in most org. solvs. barely sol. in water m.w. 650 sp.gr. 0.977 (40 C) acid no. 0.05 hyd. no. 166.2-179.5 flash pt. 215 C 0.025% water Storage Hygroscopic protect from moisture and air dry nitrogen blanket should be applied to open containers before resealing Polythix M [Poly-Resyn]... 

Chem. Descrip. Polyether PU coating in DMFAoluene Uses Heat-seal base coat for nylon and polyester fabrics, providing soft hand and exc. hydrolytic stability Featwes Designed to be used with Solucote Top 926 Properties Clear vise. 30,000 5000 cps 100% tens. mod. 350 psi tens. str. 2700 psi elong. 725% 41 2% solids Solucote Base 128 [SoluoQ... 

Classification Thermoplastic elastomer Definition Polymer consistg. of hard segments embedded in a soft, elastomeric polyol phase exc. abrasion/impact resist. high str. wide working temp, range good hydrolytic stability two types polyether- or polyester-based Properties Solid... 

The polyether types are slightly more expensive and have better hydrolytic stability and low temperature flexibility than the polyester types. 

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