NOVEL ALTERNATING COPOLYMERS OF CONJUGATED DIENES AND CONJUGATED POLAR VINYL MONOMERS, WHEREIN THE CONJUGATED DIENE UNIT IS CONNECTED IN A TRANS-1,4 FORM AND THE CONJUGATED POLAR VINYL MONOMER UNIT AND THE CONJUGATED DIENE UNIT ARE BONDED ALTERNATELY, ARE PRODUCED EFFICIENTLY BY COPOLYMERIZING THESE MONOMERS IN A NON-AQUEOUS MEDIUM AT RATHER LOW TEMPERATURE BY USING A CATALYST SYSTEM PREPARED BY ADMIXING A SELECTED TRANSITION METAL COMPOUNDS AND AN ORGANOALUMINUM HALIDE IN THE PRESENCE OF THE POLAR VINYL MONOMER OR ANOTHER SELECTED LEWIS BASE. THE LATERNATING COPOLYMER HERE OBTAINED HAS A REGULAR STRUCTURE, ON THIS ACCOUNT, FOR EXAMPLE, THE BUTADIENE/ACRYLONITRILE ELASTIC ALTERNATING COPOLYMER CAN BE ORIENTED AND CRYSTALLIZED UNDER A HIGHLY STRETCHED CONDITION.