ABSTRACT:A saturated star-shaped poly(ethylene-co-propylene) copolymer, (EP) star , has been synthesized for use as a viscosity index improver in lubricants. Polyisoprene arms were first anionically synthesized using n-butyllithium as the initiator, followed by a linking reaction with divinylbenzene at the optimum temperature of 60°C. The resulting star-shaped polyisoprene, (I) star , was then hydrogenated to eliminate the double bonds of the polyisoprene forming the poly(ethylene-co-propylene) structure. The degree of branching (number of arms on each molecule) increases with increase in the mole ratio of divinylbenzene to n-butyllithium. Increasing the arm length adversely affects the linking efficiency and a minimum amount of tetrahydrofuran (THF) at a THF:n-butyllithium molar ratio of 1.12 was needed in order to achieve a maximum linking efficiency of approximately 85%. The T g of poly(ethylene-co-propylene) is about 10°C higher than that of the original polyisoprene. Compared with (I) star , (EP) star has a thermal decomposition temperature that is 50°C higher but is independent of the arm length or the degree of branching. Viscosity measurement results for (EP) star reveal that intrinsic viscosity depends only on the arm length but not the degree of branching. Adding 1 wt % of (EP) star markedly increases the viscosity index of a LN base oil. The addition of 1 wt % of (EP) star increases the viscosity index (95 for base oil) up to a number between 111 and 145, with the exact number depending upon its arm length and degree of branching. With a fixed arm length, an (EP) star having a higher degree of branching increases the viscosity index more than one having a lower degree of branching. On the other hand, the viscosity index increases with increase in the arm length when the degree of branching is fixed. Adding 1 wt % of (EP) star also causes a change in the pour point of the lubricant with the pour point decreasing with increase in the degree of branching.
Three new amino-s-triazine-based dendrons, 1a, 1b, and 1c, containing an aryl-CN moiety in the dendritic skeleton were prepared in 72–81% yields (1a: R1 = − N(n-C8H17)2, R2 = n-OC8H17, 1b: R1 = R2 = − N(n-C8H17)2, 1c: R1 = − N(n-C8H17)2, R2 = − N(n-C4H9)2). Dendrons 1a with N(n-C8H17)2 and n-OC8H17 peripheral substituents, surprisingly, did not show any mesogenic phase during the thermal process. However, non-mesogenic 1a can be converted to mesogenic 1b or 1c by eliminating the peripheral dipole arising from the alkoxy substituent; dendron 1b only comprising the same N(n-C8H17)2 peripheral groups showed a ~25 °C mesogenic range on heating and ~108 °C mesogenic range on cooling. In contrast, dendron 1c possessing different N(n-CmH2m+1)2 (m = 8 versus m = 4) peripheral units, having similar stacking as 1b, exhibited a columnar phase on thermal treatment, but its mesogenic range (~9 and ~66 °C on heating and cooling, respectively) was much narrower than that of 1b, attributed to 1c’s less flexible alkyl chains in the peripheral part of dendron. Dendron 1a with the alkoxy substituent in the peripheral skeleton, creating additional dipole correspondingly, thus, leads to the dendritic molecules having a non-mesogenic stacking. Without the peripheral dipole for intermolecular side-by-side interaction, dendrons 1b and 1c exhibit a columnar phase on thermal treatment because of the vibration from the peripheral alkyl chain.
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