Polyether Polyols
The two major families of polyether polyols are polytetramethylene ether glycols (PTMEG) and polypropylene glycols (PPG).
PTMEG is the premier polyol used in high-performance polyurethane elastomers. PTMEG-based polyurethanes exhibit superior resistance to hydrolytic cleavage, good mechanical properties retention at low temperature, high resiliency, good processing characteristics, and excellent mechanical and dynamic properties. Strain-induced crystallization of the PTMEG soft segments, exact difunctionality, and low acid values are all contributing factors to the good mechanical properties of the associated polyurethane elastomers.
PPG polyols have excellent hydrolysis resistance and low temperature properties as well. However, when compared to PTMEG polyols, the PPG polyols have inferior mechanical properties and are more prone to thermo-oxidative degradation.
Being in a liquid state at room temperature, PPG polyols make an excellent choice for room temperature systems.
Polyethers have low glass transition temperature (Tg), which imparts good retention of physical properties and impact resistance at low temperatures. They are the proper choice for applications where urethane parts are expected to perform in very cold environments.
Although polyether polyols exhibit excellent hydrolytic stability, they have poor resistance to non-polar, hydrocarbon-based solvents and should not be used in applications where the parts will be exposed to mineral oils. In these environments, their properties will deteriorate relatively quickly.
PTMEG-based urethanes are the material of choice for applications where the following properties are important:
Good impingement abrasion (high resiliency)
Hydrolytic stability in humid/wet conditions
Good dynamic properties (wheels, rollers, roll covers)
Low temperature applications
Furthermore, PTMEGs have relatively low viscosities, making them easy to process and achieve good mixing.