UCST-Type Thermoresponsive Polymers in Synthetic Lubricating Oil Polyalphaolefin (PAO)

This Article reports a family of UCST-type thermoresponsive polymers, poly­(alkyl methacrylate)­s with an appropriate alkyl pendant length in an industrially important nonvolatile organic liquid polyalphaolefin (PAO). The cloud point (CP) can be readily tuned over a wide temperature range by changing the alkyl pendant length; at a concentration of 1 wt % and similar polymer molecular weights, the CP varies linearly with the (average) number of carbon atoms in the alkyl pendant. PAO solutions of ABA triblock copolymers, composed of a PAO-philic middle block and thermoresponsive outer blocks with appropriate block lengths, undergo thermoreversible sol–gel transitions at sufficiently high concentrations. The discovery of thermoresponsive polymers in PAO makes it possible to explore new applications by utilizing PAO’s unique characteristics such as thermal stability, nonvolatility, superior lubrication properties, and so on. Two examples are presented: thermoresponsive physical gels for control of optical transmittance and injectable gel lubricants.