Investigations of volume photopolymerization in big diameter round dilatometer are carried out. The methods of experiment allowing in regular intervals to irradiate a solution from, different sides are offered. The theory of photopolymerization. processes for any values of initiator optical density is proposed. On the basis of theoretical and. experimental studies of a photoinitiated polymerization by pentazadienes is shown, that photopolymerizations kinetics at initiator big values of optical density contains last and slow components, and the fast one corresponds to dilatometer surface polymerization, and the slow one - to reaction front movement inside the dilatometer. It is shown, that due to computer simulation. of photopolymerization kinetics molecular weight distribution is possible to calculate. It is found, that during the polymerization distribution of macromolecules yields on polymeric chain lengths is kept constant.