Copolymers in general exhibit physical and mechanical properties far different from those of homopolymers and different from those of blends of the same individual homopolymers. Pyrrole (Py) 3 was grafted onto a poly(vinyl acetate) (PVAc) backbone that contained the Py moiety within via chemical and electrochemical oxidative polymerization. Graft copolymer 4 was soluble with low Py amounts but became rapidly insoluble with increasing Py content due to the formation of long Py sequences. The maximum conductivity of films cast from the reaction mixture was 8.3 x 10(-3) S/cm. The product 4 was characterized and studied in detail using elemental analysis, ATR, H-1-NMR, UV-visibility, gel permeation chromatography (GPC), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), and scanning electron microscopy (SEM). Gas sensors based on conducting polymers that exhibit electrical conducting properties can be used as specific toxic gas and vapor detectors. We report here effects of conductance and mass changes onto a graft copolymer 4 after exposure to hydrogen halides, hydrogen cyanide, 1-3-5 trichloromethyl benzene (TCMB), methylbenzyl bromide (MBB), bromobenzyl cyanide (BBC), cyanogen chloride (CC), and cyanogen bromide (CB), using two techniques: a four-point probe method and a X-ray fluorescence (XRF) device, respectively. Increasing of ratio polypyrrole (PPy) in the graft copolymer 4 increase the sensing properties of this copolymer and decrease the solubility of it. (C) 2003 Wiley Periodicals, Inc.