Polyether-Based Polyurethanes

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. 

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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. 

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. 

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. 

For polyether-based polyurethane at 70 to 80°C, the properties are only 50% of the original, whereas at 110°C the value drops to about 20%. This gives a normal safe working temperature of 80°C. Figure 7.10 illustrates the aging effect on different cure systems. This working range can be increased by the use of isocyanates such as PPDI in the polyurethane (Chin et al., 1992). 

The Panama weathering study has shown polyester polyurethanes to be prone to fungus attack within 6 months. Polyether-based polyurethanes are resistant to such attacks. If specific work is required, it is best that it is carried out by a suitably competent consulting laboratory. 

Adiprene Polyether-based polyurethane (elastomer) Du Pont... 

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. 

Polyurethanes were prepared by both prepolymer and oneshot methods. Our poljraiers were molded at about 190° C Into 0.3 mm sheets. A commercial supplier provided 0 25 mm sheets of polyester based and polyether based polyurethanes. These were used as received, except for cutting. 

Phase Development During Polymerization. Polyether based polyurethanes are known to phase separate faster than those based on polyester soft segments. Indeed, formulations like those used in this work become opaque during the polymerization indicating that domain superstructures (14) have formed. Development of this opacity has been used (], ) to indicate phase separation during the polymerization although questions arise as to whether formation of small domains that do not scatter visible light occur before this. 

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]. 

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... 

Nevertheless, polyether-based polyurethanes have been found to degrade when implanted for long periods (1). The degradation is manifested in terms of surface or deep cracking, erosion, or deterioration of mechanical properties, such as flex life. 

Figure 5.2. Small-angle x-ray diagrams for a polyether-based polyurethane as a function of...

There are important differences between materials and differences among similar materials within a given generic class. These differences are due to the chemical composition of the polymer, the molecular configuration of the polymer and the presence of functional groups. For instance, polyurethanes of a polyester base were initially tried and found unstable for implantation whereas polyether based polyurethanes were decidedly... 

TYPICAL ELECTRICAL PROPERTIES OF POLYETHER-BASED POLYURETHANE ELASTOMER (ADIPRENE), HARDNESS = 90 IRHD... 

Sadeghi M, Semsarzadeh MA, Barikani M, Pourafshari Chenar M (2011) Gas separation properties of polyether-based polyurethane-silica nanocomposite membranes. J Membr Sci... 

Polyether based polyurethanes are less susceptible to loss of physical properties due to microbial attack than are the polyester types. 

Lin J R and Chen L W, Study on shape-memory behavior of polyether-based polyurethanes, Appl. Poly. ScL, 1998, 69, 1563 74. 

Leung, L. M., Koberstein, J. T. (1986), DSC annealing study of microphase separation and multiple endothermic behavior in polyether-based polyurethane block copolymers. 

Lin, J. R., Chen, L. W. (1998b), Study on shape-memory behaviors of polyether-based polyurethanes. Part I Influence of the hard-segement content, J. Appl. Polym. Sci., 69,... 

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