There is provided a method for making swellable particles, said method comprising mixing initial particles, at least one monomer, at least one initiator, and at least one chain-transfer agent, wherein said mixing is performed under conditions in which said monomer is capable of forming oligomer or polymer or a mixture thereof. Also provided are swellable particles made by that method. Further provided is a method of making polymeric resin particles comprising mixing at least one subsequent monomer to those swellable particles and polymerizing said subsequent monomer.