HEIDELBERG, Germany (May 24)—Three companies have joined the International Institute of Synthetic Rubber Producers, increasing the organization´s membership to 51 following the loss of two members last year. The new members are: Sibur, the Siberian-Ural Oil, Gas & Chemicals Co., one of Russia´s biggest petrochemical producers and a maker of styrene-butadiene rubber; P.T. Sentra Sintetikajaya, an emulsion SBR producer from Indonesia; and DSM Elastomers Asia, an EPDM producer based in Singapore with production in Tokyo. Advanced Elastomers Systems L.P., the thermoplastic elastomer joint venture of Monsanto Co. and Exxon Chemical Co. based in Akron, dropped out of the IISRP in the past year, according to James McGraw, IISRP managing director and CEO, who presided over the organization´s Annual General Meeting in Heidelberg. Also leaving was HIP Petrohemija, an emulsion SBR maker located in Zrenjanin, Yugoslavia, whose plant was damaged during the Kosovo crisis, McGraw said.