A dispersant is prepared from an amine and a hydrocarbyl-substituted acylating agent, wherein the hydrocarbyl substituent is a polymerized olefin having a polydispersity M.sub.w /M.sub.n of greater than 5. Such polyolefin substituents are prepared by polymerization of olefins in the presence of a calcined catalyst comprising a partially or fully neutralized ammonium salt of a heteropolyacid.