Synthesis and characterization of isocyanate-functionalized PVA-based polymers with applications as new additives in lubricant formulations

摘要

This work deals with the incorporation of reactive isocyanate groups into polymer additives, which could be potentially used to modify the rheological properties of lubricating greases by reinforcing the role of traditional thickening agents. Thus, a batch of partially protected poly(vinylalcohol) (PVA) copolymers was successfully synthesized. Some of their -OH groups were blocked as tetrahydropyranyl (THP) ethers (PVA-THP), while the spare hydroxyl groups were further functionalized with -NCO pendant groups by reaction with 1,6-hexamethylene diisocyanate, leading to several isocyanate-functionalized PVA-based polymers (PVA-THP-NCO), which were tested as rheology modifiers of lithium lubricating greases. The highest protection degree of hydroxyl groups achieved as THP-ether was 58.5% and the recovered polymers were isolated with excellent yields (close to 90% in most cases). NCO-functionalized PVA-based polymers (PVA-THP-NCO) exerted a significant rheological modification in lithium 12-hydroxystearate lubricating greases, increasing the values of the linear viscoelastic functions. The influence of the degree of protection and later functionalization of PVA on the rheological properties of PVA-THP-NCO- additivated lubricating greases is discussed.