US Patent 7615521 Mixed dispersants for lubricants

A dispersant composition comprising the product of an amine, an alcohol, or an amino alcohol, with a hydrocarbyl-substituted succinic anhydride component exhibits improved viscosity stability and reduced chlorine content, when the hydrocarbyl-substituted succinic anhydride component comprises: (a) 10 to 95 weight percent of a component prepared by reacting a polyisobutylene with maleic anhydride in the presence of chlorine; and (b) 5 to 90 weight percent of a component prepared by reacting a polyisobutylene with maleic anhydride in the substantial absence of chlorine.