Polycaprolactone polyols comprise a special class of aliphatic polyester polyols, used as the soft block segment of high-performance polyurethane elastomers. We can produce polycaprolactone polyols with very low acid values (increasing hydrolytic stability); perfect end-termination functionality (excellent reactivity and high molecular weights); narrow molecular weight distributions (low viscosity including in the prepolymer form), and using a wide variety of initiator molecules that allow the design of customized features.
Standard adipate polyols arise from the condensation reaction of a diol with a diacid such as adipic acid. This results in side-reactions and residual acidic moieties that promote hydrolysis.
Further, the linear, symmetrical polycaprolactones repeat structural unit produces soft blocks with very high intermolecular chain-packing forces and efficient phase separation from the hard block urethane segments. This enhances flexibility, toughness, and elastomeric characteristics.
These structural features of the polycaprolactone polyols, and the even-numbered carbon spacing, are responsible for performance levels and durability that surpasses that of adipate-based polyester polyurethanes,
We have listed below just a few of the "initiator" diols (R-[-OH]f]) that formulators use and the key characteristics of the resulting polycaprolactone polyols in a polyurethane elastomer.
o Ethylene Glycol: General purpose initiator affording a good balance of properties
o Diethylene Glycol: Contributes some polyether performance characteristics and liquid diols
o Butanediol: High cut, tear and chunk resistance, high tensile properties
o Hexanediol: High tensile and thermal properties and cut-chip resistance
o Neopentyl Glycol: Reduced propensity to crystallize and better hydrolytic stability
o Polycarbonate Diol: Reduced moisture absorption and enhanced hydrolytic stability
Superior resistance to hydrolysis
Excellent weatherability and UV stability
High temperature performance
Good low temperature properties & flexibility affording a broad service temperature profile
Flex-fatigue life and elastic memory
Compression set resistance
Enhanced abrasion and impact resistance
Chemical resistance to oils, fuels, & solvents
Cut, chip, and tear strength
Processing advantages
Prepolymer viscosity stability
Excellent service life when compared with PURs based on other polyols