Nylon 3 synthesized by ring opening polymerization with a metal-free catalyst

We have synthesized nylon 3 via ring opening polymerization of 2-azetidinone (β-lactam) with 1-tert-butyl-4,4,4-tris(dimethylamino)-2,2-bis[tris(dimethylamino)- phosphoranylidenamino]-2Λ5,4Λ5-catenadi(phosphazene) (t-BuP₄) as the catalyst in a mixture of dimethylacetamide (DMAc) and LiCl. The polymers have been characterized by nuclear magnetic resonance spectroscopy (NMR), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), laser light scattering (LLS) and viscometry. The synthesized nylon 3 is a linear and crystalline polymer with a molecular weight as high as 10⁵ g mol⁻¹. The intrinsic viscosity ([η]) relates to the weight average molecular weight (M_w) as [η] = 1.02 × 10⁻⁴M_w^0.91. The effects of solvent, temperature and catalyst concentration on the polymerization have been examined. The molecular weight and yield increases with the amount of LiCl in the polymerization mixture, but both of them decrease with temperature at a temperature above 50 °C. As the catalyst concentration increases, the yield and the molecular weight of nylon 3 decrease. The possible mechanism for the initiation of polymerization is discussed.