Copolymers containing vinylpyrrolidone and mono and dialkyl itaconate units with different length in the side chains were synthesized and characterized. Copolymers of vinylpyrrolidone with three different compositions of monomethyl, monoethyl, monopropyl, monoamyl, dimethyl, diethyl, dipropyl, and diamyl itaconate were obtained by radical polymerization. The reactivity ratios was estimated by using the classical Fineman-Ross and Kelen Tudos procedures. These parameters were also estimated using a computer program based on nonlinear minimization algorithm, starting from the values of r(1) and r(2) obtained by the linear procedures. The copolymers can be considered as random. Fractionation of the copolymers were achieved by fractional precipitation. Fractions were characterized by viscometry and light scattering measurements. The unperturbed dimensions were determined using the Stockmayer-Fixman method. Higher rigidity indexes and characteristic ratios are observed in copolymers containing diitaconate units than that with monoitaconate moieties. The dependence of the glass transition temperature T-g with copolymer composition and its correlation with the chain stiffness is also analyzed.