1. IN A POLYMERIZATION PROCESS WHEREIN A MONOMER SELECTED FROM THE CLASS CONSISTING OF A-OLEFINIC COMPOUNDS AND KETONES HAVING NOT MORE THAN 35 CABON ATOMS AND OLEFIN OXIDES, LACTONES AND ALDEHYDES HAVING NOT MORE THAN 18 CARBON ATOMS IS CONTACTED AT POLYMERIZING TEMPERATURES WITH A POLYMERIZATION CATALYST TO PROVIDE A POLYMERIC PRODUCT, THE IMPROVED CATALYST FOR THE POLYMERIZATION REACTION WHICH IS A PHOSPHIDE SELECTED FROM THE CLASS CONSISTING OF COMPOUNDS OF THE FORMULAS R(N)PM(3-N) AND M(2-A)(R(A))P-R''-P(R(A))M(2-A) WHEREIN R AND R'' ARE HYDROCARBON RADICALS FREE OF NONBENZENOID UNSATURATION, R HAS NOT MORE THAN 18 CARBON ATOMS, R'' HAS NOT MORE THAN 8 CARBON ATOMS, M IS SELECTED FROM THE CLASS CONSISTING OF SODIUM, POTASSIUM AND LITHIUM, N IS AN INTEGER OF 1 TO 2, AND A IS AN INTEGER FROM 0 TO 1.