Physical-chemical studies on a sample of NCH3-imidized poly(methyl methacrylate) (PMMA-I-CH3) were performed by several characterization techniques. Fractional precipitation by solvent/non-solvent at constant temperature was used, obtaining 12 fractions characterized by different molecular weights. With these fractions of the PMMA-I-CH3, in the range 2 x 10(4) < M(w) < 2 x 10(5), a Mark-Houwink equation was determined. This relationship, in tetrahydrofuran at 30 degrees C, was found to be [eta] = 2.22 x 10(-4)M(w)(0.66). This equation is the starting point for studying the polymer-structure relationships. The determination of various properties, such as viscosity, glass transition temperature, nitrogen content and molecular weights, allowed us to obtain structural information on the copolymer. The imidization degree, evaluated by H-1 n.m.r. spectroscopy, was used to correlate glass transition temperature and polymer structure.