Controlled architecture polymers made preferably with acrylamide type monomers are prepared in living-type or semi-living-type free radical polymerizations, with the architecture preferably being other than linear, such as star, branched, grafted or hyper-branched. The controlled architecture polymers have high weight average molecular weights and low viscosities, which make they particularly useful in replaceable capillary electrophoresis separation media for biological molecules, such as DNA fragments.