Fuel cells represent a source of clean energy generation alternative to current technologies for the use of hydrocarbon fuels. As a result, polymer electrolytic membrane fuel cells (PEMFCs) have acquired great importance in recent years, especially for applications where a quick start is required, such as in automobiles. One of the main components of a PEMFC is the polymeric electrolyte, on which, the main requirements are high proton conductivity, low methanol/water permeability, good mechanical and thermal stability and, of course, moderate price. In our research group, in the line of work on the development of polymeric electrolytes, we have developed a new polymeric electrolyte derived from tetrazole. Recent results demonstrate high ionic conductivity from this copolimers. However, the mechanical properties need to be adjusted to improve the applicability of this system. Therefore, we prepared tetrazole copolymers (StVTz) with side chains with 4, 6 and 8 carbon atoms, which were introduced into the polymer chain through alkylation reactions. The alkylation was carried out with percentages of 10% on the amount of tetrazole present in the polymer. The alkylated polymers were characterized in terms of chemical structure and their thermal, mechanical and electrical properties were determined. According to the GPC, the terpolymers presented MW values greater than 200,000 g/mol. The DSC thermal analysis indicated Tg values from 70 to 110 °C, depending on the alkylated comonomer content and the length of the polymer chain. TGA analyzes for all copolymers showed decomposition temperatures above 195 °C. Ionic conductivity was determined by impedance. A dependence is observed between the amount of free tetrazole and the conductivity of the electrolite. Mechanical properties are strongly dependent on side chain length and percentage of alkylation. The alkylated copolymer with the best relationship between thermal properties, mechanical properties and ionic properties is StVTz copolymers with a side chain of 4 carbon atoms in 10% substitution in which the ionic conductivity was 75 x10-3 mS.cm-1. For these copolymers the mechanical strength was 1522 MPa for the dehydrated polymer and 894 MPa for the hydrated polymer. This same copolymer was also the most thermally stable, being approximately 50 °C more stable than the unalkylated copolym