Low Temperature and Thermal Performance
Polyethers have lower glass transition temperature (Tg) and better retain their flexibility and impact resistance at low temperatures. Polyesters, meanwhile, exhibit better thermo-oxidative stability and property retention at elevated temperatures.
Resilience
Polyether-based polyurethanes generally exhibit higher rebound (resilience) compared to their polyester-based counterparts.
Dynamic and Mechanical Properties
In applications requiring products with higher tensile strength and cut and tear resistance, polyesters are the preferred polyols. Polyethers impart lower hysteresis or heat buildup, which makes them a preferred material for dynamic applications like wheels, casters and rollers.
Abrasion Resistance
Abrasion wear is most often a result of the combination of sliding and impingement abrasion. There are numerous abrasion tests designed to accurately predict a material's service performance, as many different factors can impact abrasion performance of urethane elastomers. Selecting the right abrasion test, which will most closely correspond with the actual end-use application, can thus be quite challenging.
Polyether-based polyurethanes, due to their higher resilience, offer better performance in applications where impingement abrasion is the dominant form of wear. This performance dynamic is especially true for PTMEG based elastomers.
In a general sense, the higher tensile and tear resistance of the polyester-based polyurethane materials offer an advantage in applications where sliding is the dominant form of abrasion.
The environment in which the material is expected to perform must also be considered. A potential for hydrolysis on the surface of the ester-based polyurethanes, for example, will negatively impact their long-term abrasion resistance.
Processing Characteristics
PTMEG polyols are exact difunctional primary diols exhibiting several key attributes for processing. PTMEG polyols exhibit a very low degree of acidity. Their melting points measure at below room temperature for low molecular weight grades, such as PTMEG 650. Higher molecular weight grades melt slightly above room temperature, and they exhibit lower viscosity because their molecular weight distribution is narrower. Furthermore, PTMEG polyols promote consistency in the production of polyurethanes.
PPG polyols are not exact difunctional and contain levels of mono-functionality. They also have secondary hydroxyl moieties which are lower in reactivity. Accordingly, their molecular weight distribution and viscosity is higher than PTMEG based polyurethanes, and the molecular weights achieved are generally lower.
Finally, polyester polyols can have high melting points and higher degrees of acidity, which affect catalyst reactivity. These polyols exhibit broad molecular weight distributions and viscosities.