Mitsui Chemicals Inc. (TYO:4183) has recently announced that it will step up its market development efforts for a highly heat-resistant metallocene-based grade of ethylene propylene diene monomer (EPDM) rubber in a move to boost sales. The chemical giant’s heat-resistant grade of EPDM rubber is able to withstand temperatures 30 degrees higher than conventional alternatives. Last fiscal year, the company started…