A polymer activation assembly is provided for separating monomer from the oil in which it is suspended in a polymer forming suspension and mixing the monomer with water supplied from another stream. The supply water is supplied through a primary fluid channel extending through the activation assembly and which transitions to a relatively wide rectangular activation channel. A secondary fluid inlet is formed in a side of the activation assembly for injection of the polymer forming suspension therein. A nozzle section of the secondary fluid inlet is formed between an initial section of the inlet and the activation channel. The nozzle section is generally rectangular in cross section and relatively shallow. The distal end of the nozzle section has a width that approximates the width of the activation channel. The nozzle section angles at an acute angle toward the outlet.