Polyether-based

Crown 4 and 18 crown 6 are a cyclic tetramer and hexamer respectively of repeat mg —OCH2CH2— units they are polyethers based on ethylene glycol (HOCH2CH2OH) as the parent alcohol... 

Foams prepared from phenol—formaldehyde and urea—formaldehyde resins are the only commercial foams that are significantly affected by water (22). Polyurethane foams exhibit a deterioration of properties when subjected to a combination of light, moisture, and heat aging polyester-based foam shows much less hydrolytic stabUity than polyether-based foam (50,199). 

Fully cured polyurethanes present no health ha2ard they are chemically inert and insoluble in water and most organic solvents. However, dust can be generated in fabrication, and inhalation of the dust should be avoided. Polyether-based polyurethanes are not degraded in the human body, and are therefore used in biomedical appHcations. 

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

Both polyethers and polyesters may be used as polyols. For example, Du Pont use polytetrahydrofuran for Lycra whilst US Rubber originally used a polyester of molecular mass of about 2000 obtained by condensing adipic acid with a mixture of ethylene and propylene glycols. A polyether-based mixture was used for Vyrene 2 introduced in 1967. All the polyols have terminal hydroxyl groups. 

Polyether-based thermoplastic polyurethane elastomers (Section 27.4). 

The minimum service temperature is determined primarily by the Tg of the soft phase component. Thus the SBS materials ctm be used down towards the Tg of the polybutadiene phase, approaching -100°C. Where polyethers have been used as the soft phase in polyurethane, polyamide or polyester, the soft phase Tg is about -60°C, whilst the polyester polyurethanes will typically be limited to a minimum temperature of about 0°C. The thermoplastic polyolefin rubbers, using ethylene-propylene materials for the soft phase, have similar minimum temperatures to the polyether-based polymers. Such minimum temperatures can also be affected by the presence of plasticisers, including mineral oils, and by resins if these become incorporated into the soft phase. It should, perhaps, be added that if the polymer component of the soft phase was crystallisable, then the higher would also affect the minimum service temperature, this depending on the level of crystallinity. 

Thermoplastic polyurethane elastomers have now been available for many years (and were described in the first edition of this book). The adipate polyester-based materials have outstanding abrasion and tear resistance as well as very good resistance to oils and oxidative degradation. The polyether-based materials are more noted for their resistance to hydrolysis and fungal attack. Rather specialised polymers based on polycaprolactone (Section 25.11) may be considered as premium grade materials with good all round properties. 

Whilst approximately twice the raw material cost of TPO- and S-B-S-type polymers, thermoplastic polyurethane elastomers find applications where abrasion resistance and toughness are particular requirements. Uses include gears, timing and drive belts, footwear (including ski boots) and tyre chains. Polyether-based materials have also achieved a number of significant medical applications. There is also some minor use as hot melt adhesives, particularly for the footwear industry. 

The PSA formulator can also take advantage of plasticizers. For example, polyether-based plasticizers have both good low-temperature flexibility and good hydrophilicity. Using these properties, acrylic PSAs have been formulated with these types of plasticizers to obtain high adhesion to food packages stored under refrigerated conditions [102]. Similarly, polyether plasticized acrylics have been used to make repulpable PSAs [103]. 

Both polyester- and polyether-based TPU could be used to blend with PVC, although the former constitutes the majority of the commercial products. All of the blends should meet the following requirements (I) they must have good or relatively good compatibility with PVC, (2) their processing temperature should be close to or lower than that of PVC, (3) they have to meet the specific requirements of the products, for example, TPUs used for medical purposes should be colorless (if possible), transparent, nontoxic, and able to be sterilized, and (4) they should not be expensive. 

The focus has largely been on polyether-based solvent-free systems for lith-... 

The polyether-based polyurethanes are now of greater commercial importance then those based on polyesters. A frequently used polyether is that derived from propene oxide, as illustrated in Reaction 4.9. 

Polyether-based thermoplastic copolyesters show a tendency toward oxidative degradation and hydrolysis at elevated temperature, which makes the use of stabilizer necessary. The problem could be overcome by incorporation of polyolehnic soft segments in PBT-based copolyesters [31,32]. Schmalz et al. [33] have proposed recently a more useful technique to incorporate nonpolar segments in PBT-based copolyesters. This involves a conventional two-step melt polycondensation of hydroxyl-terminated PEO-PEB-PEO (synthesized by chain extension of hydroxyl-terminated hydrogenated polybutadienes with ethylene oxide) and PBT-based copolyesters. 

Besides the polyether-based polymer electrolytes, the nitrogen analogues (polyimines) were also extensively studied. Various other oxygen-containing... 

The general molecular structure of polyether-based polyurethanes is illustrated in Fig. 25.3 a). Typical polyether sequences include polyethylene glycol and polypropylene glycol. The length of the polyether sequences between urethane links can vary from one or two ether groups up to several hundred. As the length of the polyether sequences between urethane links increases, the polymer exhibits more of the properties normally associated with polyethers. 

Polyether-based foams account for more than 90% of all flexible polyurethane foams. The properties of foams are controlled by the molecular structure of the precursors and the reaction conditions. In general, density decreases as the amount of water increases, which increases the evolution of carbon dioxide. However, the level of water that can be used is limited by the highly exothermic nature of its reaction with isocyanate, which carries with it the risk of self-ignition of the foamed product. If very low density foams are desired, additional blowing agents, such as butane, are incorporated within the mixing head. 

Another major use for semi-rigid polyurethane foams is as shoe soles. In this application, their light weight, abrasion resistance, and shock absorbing properties are important. In safety shoes, chemical and oil resistance are important. Polyether-based foams are used in applications where microbial attack is common, such as shoes intended primarily for use on soil or grass. 

The most important physical characteristics of polyurethane elastomers are their elasticity, low permanent set, high tear strength, and good abrasion resistance. Polyester-based elastomers have higher tear strength than polyether-based analogues. Polyether-based elastomers have better recovery. Important chemical characteristics include stability when exposed to the elements and resistance to oil and grease. 

Wheels and tires are one of the major uses of cast polyurethane elastomers. We commonly see these on fork lift trucks and shopping carts, where their excellent abrasion resistance, resistance to oil, and good elasticity are valued. In industrial settings we find polyurethane covers on rollers used for paper, steel, and textile conveyor systems. In such applications, their excellent cut and abrasion resistance help prolong their useful life. If used in hot and humid conditions, polyether-based polyurethanes are preferred. 

Describe the differences in properties between polyester and polyether based polyurethanes. 

Percec et al. have described the possibility of making hyperbranched polymers which exhibit liquid crystalline phases [34, 35]. They made hyperbranched polyethers based on an A B monomer having both a spacer and a... 

Abstract PAMAM types polyether based dendrimers were synthesized from three branched Jeffamines . Synthesized compounds bears metylester/ferf-butylester, caiboxylic acid or amine groups. In the synthesis iterative Micheal type of reaction paths were followed. Catalytic properties of the molecules were studied in homogenous phase. 

Miyamoto and Shibayama (1973) proposed a model which is essentially an extension to free volume theory, allowing explicitly for the energy requirements of ion motion relative to counter ions and polymer host. This has been elaborated (Cheradame and Le Nest, 1987) to describe ionic conductivity in cross-linked polyether based networks. The conductivity was expressed in the form... 

Despite the initial misinterpretation in the ion conduction mechanism, it was soon realized that the ion conduction in PEG and other similar polyether-based media mainly occurred in the amorphous phases. Increasing evidences were obtained that ionic motion in these polymer ion conductors was closely... 

Polyurethane hydrogels derived from UV curable urethane prepolymer and hydrophilic monomers were prepared and their properties were evaluated. The urethane prepolymer used in this study contained well-defined hard segments centered with a polyether-based soft segment and end-capped with methacrylate groups. The hydrophilic monomers studied were 2-hydroxyethyl methacrylate (HEMA), N-vinyl pyrrolidone, and glycerol methacrylate. Methacryloxypropyl tris(trimethysiloxy) silane (TRIS) was also used in some cases to modify properties. All compositions were UV... 

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