An unusual kinetics of anionic polymerization of four-membered lactams

The anionic polymerization of α,α-disubstituted four-membered lactams (3-hexyl-3-methyl-2-azetidinone, I and 3-butyl-3-methyl-2-azetidinone, II) was found to follow a more complicated kinetics than could be expected. The apparent order of polymerization with respect to the monomer was not constant and increased from zero at the beginning of polymerization to two towards its end. Therefore, it is justified to correlate only the initial rate of polymerization with the concentrations of reactants.