EMI will begin to conduct business as EMD Chemicals Inc. effective Jan. 1, as part of a strategy being implemented by its parent company, Merck KGaA (Darmstadt, Germany), to unite its NA operations under the EMD brand.   . . .   Michael O'Neill, global business segment manager at Heraeus Inc.'s Circuit Materials Div., has been named chairman of the Microelectronics Marketing Research Council (MMRC), and Howard Imhof, vice president of marketing and sales at Midas Vision Systems, has been made a member of the MMRC Steering Committee.