Well-defined homo- and copolymers of acrylonitrile were prepared by atom transfer radical polymerization, which were further modified using a "click chemistry" reaction with sodium azide and zinc chloride to yield polymeric materials with 5-vinyltetrazole units. Using optimized reaction conditions ([NaN3]:[ZnCl2]:[RCN] = 4:1:1 in DMF at 120degreesC for 48-50 h), essentially complete transformation of the nitrile groups was achieved, as judged from IR and C-13 NMR spectra. The produced tetrazole-containing polymers had markedly better solubility or swellability in protic solvents (methanol or aqueous base solutions) compared to the precursors. Random copolymers of acrylonitrile and styrene were also grown from polystyrene and silica particles with immobilized initiator groups and were similarly modified to the corresponding tetrazole-containing polymers. All materials were characterized by means of thermo-gravimetry, which showed that the polymeric tetrazoles started to decompose with evolution of significant amounts of gas at 120-190degreesC, i.e., at lower (by 60-130degreesC) temperature than the starting nitrile-based materials.