675 ISSN 1560-0904, Polymer Science, Series B, 2016, Vol. 58, No. 6, pp. 675–680. © Pleiades Publishing, Ltd., 2016. Poly(n-octyl methacrylate) Viscosity Index Improver: Kinetic Study via On-line 1 H-NMR Technique 1 Seyed Mehrdad Jalilian a , Hassan Farhadnejad b *, Farshid Ziaee a , Behrouz Furughi Nia c , Hossein Abdollahi a , and Vahid Najafi a a Iran Polymer and Petrochemical Institute, Tehran, 14975-112 Iran b Students’ Research Committee, Department of Pharmaceutics and Pharmaceutical Nanotechnology, School of Pharmacy, Shahid Beheshti University of Medical Sciences, Tehran, Iran c Dezful University of Medical Sciences, Dezful, Iran *e-mail: farhadnejad123@gmail.com Received January 27, 2016; Revised Manuscript Received June 24, 2016 Abstract– The free radical solution polymerization of n-octyl methacrylate has been studied in benzene-d 6 in the presence of 2,2'-azobisisobutyronitrile as thermal initiator. An on-line nuclear magnetic resonance spec- troscopy was applied to record the reaction data and to determine the monomer conversion at different times during the polymerization reaction. Effect of monomer and initiator concentration as well as reaction tem- perature on polymerization rate was studied. The order of the reaction with respect to initiator (0.45) was con- sistent with the classical kinetic rate equation, while the order of reaction with respect to monomer (1.87) was much greater than unity. An overall activation energy (E a = 53.8 kJ/mol) was obtained over the temperature range 328−338 K. Also, the efficiency of the synthesized poly(n-octyl methacrylate) for improving the vis- cosity index of the lube oil was investigated. DOI: 10.1134/S1560090416060087 INTRODUCTION Modern lubricants were formulated by using the base oils and chemical additives. The lubricant creates a separating fluid layer between moving surfaces and keeps friction at a low level. Many properties of the lubricants are improved or created by addition of spe- cial chemical additives to the base oil. Chemical addi- tives used in the lube oils may be classified as: viscosity index improver [1], pour point depressant [2], antiox- idant [3], corrosion inhibitor [4], extreme pressure agent [5], etc. Viscosity index improvers are liner, long chain, high molecular weight and oil soluble polymers that applied to resist the variation of viscosity the base oil by enhancing the relative viscosity of oil more at high temperatures than at low temperatures [6–9]. The efficiency of viscosity index improvers is often expressed in terms of viscosity index, which is an arbi- trary scale that shows the extent of changes in viscosity with changes of temperature [10]. The efficiency of polymers as viscosity index improvers depends on the behavior of the polymer chains in the oil solution such as polymer solubility, molecular weight, concentra- tion and structure of polymer and resistance to shear degradation [9]. The increase in the temperature of lube oil make to reduce its viscosity, but the polymer molecule expands because of the increase in the solvation power and thus, the size of micelle enhances. It counterbalances the reduction in the lube oil viscosity and, therefore, makes to decrease the change in the viscosity with the temperature. The process of coil expansion is entirely reversible [11–13]. For this purpose, homopolymers and copolymers of n-alkyl acrylates and methacrylates are often applied as pour point depressants or flow improvers, viscosity index improvers in crude and lubricating oils and etc. [14, 15]. One of the most important oil-soluble and synthetic polymers based on alkyl methacrylate is poly(n-octyl methacrylate). On the other hand, one of the most important effec- tive factors on viscosity index is molecular weight of polymer [11–13]. Thus, according to the very high importance of poly(n-octyl methacrylate) and its copolymers as polymeric additives for lube oil, it is necessary to study its polymerization kinetic precisely, to optimize the polymerization process and control the characteristics (molecular weight and molecular weight distribution) of the final product. There are several methods for kinetic studies of radical polymerization of vinylic monomers, in which one of the reaction varying factors have been followed as continual. The most usual methods can be summa- 1 The article is published in the original. SYNTHESIS