OF VISCOSITY INDEX IMPROVER ADDITIVE OF OTOMOTIVE LUBE OIL VIACOPOL YMERIZA TION OF NATURAL RUBER LATEX WITH STYRENE BY MEANS OF CHEMICAL PROCESS. Viscosity index improver is an additive used for stabilizing the viscosity of lubricating oils toward temperature change.Synthesize of this additive was carried out via copolymerization of natural rubber latex with styrene using benzoil peroxide agan initiator. The main objective of this study is to obtain a laboratory scale technology for formation of viscosity inde):improver, which in the further study the technology is able to be developed to a commercial process. The domestic oilindustries, therefore, are no longer dependent on the import products. In this study, temperature and time required fol"copolymerization process were varied to obtain optimal operating condition. The product of this process was a polymerwhich was in the form of solid layer. The polymer was characterized for physical and chemical characteristics, such a~ degre(:of grafting and functional group content. The polymer product was then chopped into fine bits and dissolved in xylen in th(:concentration ofapprox. 15 %w/v. The concentrate was rediluted with several types of lube base stocks in the composition 01150:50 (v/v). The solutions were then examined for their physical and chemical characteristics, particularly the values 0'1viscosity indexes. The solution with maximal viscosity index was selected as the best additive which was ready to be sold. Inthis study, a simple formulation of lubricating oil was also prepared by mixing the best additive solution into one of the lub(:base stocks with the composition ofapprox. 2.5 %v/v. The viscosity index of the mixture was then determined. According tothe results of analysis, the best additive solution and lubricating oil with simple formulation, have viscosity indexes ofapprox.517 and 287 respectively.Key words: Viscosity index improver, natural ruber latex, stirene, copolymerization. E. Suhardono, Redy Pelita, Rulyana Fatriasti daD Roza AdryaniP31MGB-LEMIGAS