Low-Temperature Performance and Tribological Properties of Poly(5-n-butyl-2-norbornene) Lubricating Oils: Effect of Molecular Weight and Hydrogenation on the Viscosity and Anti-Wear Activity

A series of poly(5-<i>n</i>-butyl-2-norbornene) oils with controlled molecular weights was synthesized via metathesis polymerization, fully hydrogenated, and characterized in terms of viscosity and tribological performance. In contrast to established lubricant base stocks-such as poly(α-olefins) and multiply alkylated cyclopentanes-these novel norbornene-based polymers remain underexplored, despite their promising anti-wear activity. Based on differential scanning calorimetry (DSC) data, all the synthesized products are amorphous compounds whose thermograms show a single glass transition temperature. The effect of molecular weight and temperature on the viscosity of poly(5-<i>n</i>-butyl-2-norbornene) oils was quantified over an extended temperature range, including extra-cold conditions down to -80 °C. The pour points of the oils were determined and can be as low as -66 °C, indicating excellent low-temperature fluidity. The tribological performance of the synthesized oils was evaluated using the four-ball test, with friction coefficient and wear scar diameter measured to assess anti-wear and antifriction properties. The tribological results were benchmarked against commercially available polyalphaolefin (PAO) oils (<b>PAO-4</b>, <b>PAO-20</b>, and <b>PAO-80</b>). Metathesis and hydrogenated poly(5-<i>n</i>-butyl-2-norbornene) oils outperform conventional PAOs by up to 67% in wear protection and 30% in friction reduction. These findings establish alicyclic molecular strain as a viable design parameter for next-generation lubricating oils, thereby expanding the toolbox for material development beyond conventional chemical functionalization.