5-Vinyltetrazole (VT)-based polymer is mainly produced by 'click chemistry' from polyacrylonitrile due to the unavailability of 5-vinyltetrazole monomer, which usually produces copolymers of VT and acrylonitrile rather than pure poly(5-vinyltetrazole) (PVT). In present work, VT was synthesized from 5-(2-chloroethyl)tetrazole via dehydrochlorination. A series of PVT with different molecular weight were synthesized by normal free radical polymerization. The chemical structures of VT and PVT were characterized by H-1 NMR and FTIR. PVT without any doped acid exhibits certain proton conductivity at higher temperature and anhydrous state. The proton conductivity of PVT decreases at least 2 orders of magnitude after methylation of tetrazole. PVT and PVT/H3PO4 composite membranes are thermally stable up to 200 degrees C. The glass transition temperature (T-g) of PVT/xH(3)PO(4) composite membranes is shifted from 90 degrees C for x = 0.5 to 55 degrees C for x = 1. The temperature dependence of DC conductivity for pure PVT exhibits a simple Arrhenius behavior in the temperature range of 90-160 degrees C, while PVF/xH(3) PO4 composite membranes with higher H3PO4 concentration can be fitted by Vogel-Tamman-Fulcher (VTF) equation. PVT/1.0H(3)PO(4) exhibits an anhydrous proton conductivity of 3.05 x 10(-3) at 110 degrees C. The transmission of the PVT/xH(3)PO(4) composite membrane is above 85% in the wavelength of visible light and changes little with acid contents. Thus, PVF/xH(3)PO(4) composite membranes have potential applications not only in intermediate temperature fuel cells but also in solid electrochromic device. (C) 2008 Elsevier B.V. All rights reserved.