The mass contents in five samples of a nematic azobenzene polymethacrylate having different molar masses and molar mass distributions were evaluated starting from either Logarithmic Normal (LN) or Zimm-Schulz (ZS) distribution functions. Reliability of these two approaches was verified by comparing the experimental T-g with those predicted (Fox-Flory) on the basis of the LN and ZS mass contents. A birefringent bit was induced in the various samples, and its stability on time was monitored at constant temperature. The optical bit was found to be quite stable at temperatures below that at which conformational disorder was frozen in the nematic phase.