The free radical reactivity ratios between styrene and different vinyl-1,2,3-triazole regioisomeric monomers in 1,4-dioxane at 65 degrees C have been established using nonlinear least square method. The results obtained for the reactivity ratio between regioisomers show exceptionally different polymerization behavior, highlighting the effects of the electronic and steric factors of these regioisomeric monomers. The experimental results highlight the effects of the electronic and sterics on the copolymerization behavior. In case of 1,4-vinyl-triazoles, it was found that without the steric effects, the reactivity is very similar to that of styrene and forms random copolymers. However, it was found that 1,5-vinyl-triazoles are more reactive than 1,4-vinyl triazoles. In the case of styrene-co-1,4-vinyl-1,2,3-triazoles, the reactivity ratios were calculated to be r(styrene): r(1-octyl-4-vinyl-triazole)=1.97:0.54, r(styrene) : r(1-benzyl-4-vinyl-triazole)=1.62:0.50, and r(styrene): r(1-methyl-4-vinyl-triazole)=0.90:0.87. On the other hand, reactivity ratios for styrene-co-1,5-vinyl-1,2,3-triazoles were found to be r(styrene): r(1-octyl-5-vinyl-triazole)=0.13:0.66 and r(styrene): r(1-benzyl-5-vinyl-triazole)=0.34:0.49. (c) 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 3359-3364