A new technique is reported for surface modification of polymers that is based upon photoinitiated cationic polymerization. The bulk, host sample is doped with a small amount of a cationic photoinitiator and exposed to radiation, thus creating a catalytic surface that, when exposed to an appropriate monomer, serves to initiate polymerization, thereby altering the surface properties of the bulk sample. The polymerization process is characterized by highly nonlinear growth kinetics. The effect of reaction variables on these kinetics has been explored and a molecular level model for the process is proposed. © 1985, American Chemical Society. All rights reserved.