HOUSTON (Sept. 25)—Koch Industries Inc. is buying out its partner in the KoSa polyester fiber joint venture, but the company's top executive pledged there would be no operational changes. Wichita, Kan.-based Koch said it would buy the 50-percent ownership stake in KoSa held by IMASAB S.A. de C.V. of Mexico City for an undisclosed price. Koch and IMASAB created KoSa in late 1998 to effect the buy-out of Hoechst A.G.'s polyester fibers and resins business. "KoSa's mission is unchanged, that is, to be the leader in the polyester industry," KoSa CEO George Gregory said in a prepared statement. Koch will carry out the purchase through its Koch International Equity Investments B.V. and Koch Equities Inc. subsidiaries. Among KoSa's four global businesses is technical fibers, which makes polyester and nylon cord for tire and rubber product reinforcement. The deal is expected to close in the next two months, Koch said.