Matrix Assisted Laser Desorption Ionization (MALDI) Time of Flight (TOF) Mass Spectrometry (MS) was used to study the molecular weight distribution (MWD) and the number of alpha-methyl styrene (alpha-MeSty) repeat units in SRM 1487, a narrow MWD poly(methyl methacrylate) (PMMA) standard reference material of about 6300 g/mol, which was initiated with alpha-MeSty. It was found that each PMMA polymer chain had from zero to seven alpha-MeStys per chain. The MWD of the polymer chains containing a fixed number of alpha-MeStys was obtained. The MWD, M-w, and the average number of alpha-MeSty at a given molecular weight from MALDI TOF NS compare well with those obtained from more traditional methods such as ultracentrifugation and Size Exclusion Chromatography (SEC). The implications of the number of alpha-MeStys per chain is discussed in terms of the chemistry of anionic polymerization.