Abstract: Methods for the addition polymerization of cycloolefins using a cationic Group 10 metal complex and a weakly coordinating anion of the formula: [(R′)zM(L′)x(L″)y]b[WCA]d wherein [(R′)zM(L′)x(L″)y] is a cation complex where M represents a Group 10 transition metal; R′ represents an anionic hydrocarbyl containing ligand; L′ represents a Group 15 neutral electron donor ligand; L″ represents a labile neutral electron donor ligand; x is 1 or 2; and y is 0, 1, 2, or 3; and z is 0 or 1, wherein the sum of x, y, and z is 4; and [WCA] represents a weakly coordinating counteranion complex; and b and d are numbers representing the number of times the cation complex and weakly coordinating counteranion complex are taken to balance the electronic charge on the overall catalyst complex.