EXHIBIT 4.6(B) EXTENSION AGREEMENT Arch Chemicals, Inc. 501 Merritt 7 Norwalk, Connecticut 06856 Attention: Mr. W. Paul Bush The Chase Manhattan Bank, as Administrative Agent under the 364-Day Credit Agreement referred to below 270 Park Avenue New York, New York 10017 January 26, 2000 Gentlemen: Each undersigned Lender hereby agrees to extend, effective on January 26, 2000 (the "EXTENSION DATE"), the Maturity Date under the 364-Day Credit Agreement dated as of January 27, 1999 (as the same may be amended, supplemented or otherwise modified from time to time, the "364-DAY CREDIT AGREEMENT") among Arch Chemicals, Inc., Olin Corporation, the Lenders and agents party thereto and The Chase Manhattan Bank, as administrative agent for the Lenders, to January 24, 2001. Terms defined in the 364-Day Credit Agreement are used herein as therein defined. This Agreement may be executed by one or more of the parties to this Agreement on any number of separate counterparts, and all of said counterparts taken together shall be deemed to constitute one and the same instrument. [Remainder of this page intentionally left blank] This Extension Agreement shall be governed by and construed in accordance with the laws of the State of New York. THE CHASE MANHATTAN BANK, individually and as Administrative Agent, By: /s/ Lawrence Palumbo, Jr. --------------------------------- Name: Lawrence Palumbo, Jr. Title: Vice President BANK OF AMERICA, N.A., individually and as Syndication Agent, By: /s/ Eileen C. Higgins --------------------------------- Name: Eileen C. Higgins Title: Vice President WACHOVIA BANK, N.A., individually and as Documentation Agent, By: /s/ Jane C. Deavor --------------------------------- Name: Jane C. Deavor Title: Senior Vice President 2 THE BANK OF NEW YORK By: /s/ Kenneth P. Sneider, Jr. --------------------------------- Name: Kenneth P. Sneider, Jr. Title: Vice President BANK ONE, N.A. (Main Office Chicago) By: /s/ Stephen E. McDonald --------------------------------- Name: Stephen E. McDonald Title: Senior Vice President FIRST UNION NATIONAL BANK By: /s/ Stephen T. Dorosh --------------------------------- Name: Stephen T. Dorosh Title: Vice President FLEET NATIONAL BANK By: /s/ Roger C. Boucher --------------------------------- Name: Roger C. Boucher Title Senior Vice President 3 SUNTRUST BANK By: /s/ W. David Wisdom --------------------------------- Name: W. David Wisdom Title: Vice President By: --------------------------------- Name: Title: ABN AMRO BANK N.V. By: /s/ George Dugan --------------------------------- Name: George Dugan Title: Vice President By: /s/ Patricia Christy --------------------------------- Name: Patricia Christy Title: Assistant Vice President PNC BANK, NATIONAL ASSOCIATION By: /s/ Donald V. Davis --------------------------------- Name: Donald V. Davis Title: Vice President STATE STREET BANK AND TRUST COMPANY By: /s/ K.M. O'Conner --------------------------------- Name: K.M. O'Conner Title: Vice President 4 BBL INTERNATIONAL (U.K.) LIMITED By /s/ C.F. Wright --------------------------------- Name: C. F. Wright Title: Authorised Signatories By: /s/ M-C Swinnen --------------------------------- Name: M-C Swinnen Title: Authorised Signatories 5 Agreed and accepted: ARCH CHEMICALS, INC. By: /s/ W. PAUL BUSH ------------------------------------- Name: W. Paul Bush Title: Vice President & Treasurer 6