The effect of temperature and solvent on polymer tacticity in free-radical polymerization of styrene and methyl methacrylate was studied by C-13 and H-1 NMR, respectively. Polystyrene shows a mild syndiotactic tendency (P-m = 0.36 +/- 0.02) that is independent of temperature over a wide range (-10 to 120 degrees C), while poly(methyl methacrylate) shows a stronger syndiotactic tendency (P-m = 0.17 +/- 0.01 at 30 degrees C) that decreases as temperature is increased (P-m = 0.22 +/- 0.02 at 80 degrees C). None of the polymerization solvents studied (bulk, THF, DMF, DMSO, acetonitrile, and acetone) had a significant effect on polymer tacticity in either system. The triad fractions of both polymers showed deviations from the Bernoulli model, implying that the antepenultimate unit affects the propagation reaction. (c) 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 3351-3358