A functional polymer having active and stable functional groups useful for separation or reactive processes in chemical manufacture or analysis is disclosed. The polymer comprises repeat units having structures corresponding to cycloaddition products of polymeric 1-(vinylphenyl)ethylene with electron-poor alkenes. A process for preparing the functional polymer does not require radical reactions or the exclusion of oxygen. The properties of the polymeric matrix produced can be adjusted by modifying the polymer. For example, the polymer particle size and shape, porosity, swellability, surface area, and number, type and distribution of functional groups may be controlled.