In some chain-growth polymerizations there is also a chain transfer step, in which the growing polymer chain RM° takes an atom X from an inactive molecule XY, terminating the growth of the polymer chain: RM° + XY → RMX + Y°. The Y fragment ls a new active center which adds more monomer M to form a new growing chain YM°. This can happen in free radical polymerization for chains RM°, in ionic polymerization for chains RM or RM, or in coordination polymerization. In most cases chain transfer will generate a by-product and decrease the molar mass of the final polymer.