Samples of poly (methyl methacrylate) have been made in toluene solution at −30° C withn-butyllithium initiator. Different monomer and initiator concentrations were used to obtain products of different overall molecular weights; polymerization times were varied to achieve partial as well as complete polymerization. The polymer samples were divided into fractions which were examined as to molecular weight and microstructure. It was found that the whole polymers have unusually wide molecular weight distributions which can be attributed to a combination of two narrower distributions, one of which occurs at a low and the other at a higher molecular weight region. This "double peak" phenomenon was observed for polymers at lower conversions as well as for polymers representing complete conversion of monomer. Proton magnetic resonance measurements showed that the degree of isotacticity of various fractions of a whole polymer is not the same at all molecular weights.In one case a second portion of monomer was polymerized after the complete polymerization of a first portion. Comparison of the molecular weight distribution before and after the second addition of methyl methacrylate indicated that polymer chains in all molecular weight regions, above a very low minimum value, are capable of further addition of monomer.