Poly(aminophosphazene)s and Protophosphatranes Mimic Classical Strong Anionic Base Catalysts in the Anionic Ring-Opening Polymerization of Lactams

Abstract

Linear very high molecular weight polyamides, such as nylons 6, 7 and 66, have been prepared via the rapid ring-opening polymerization (ROP) of their respective lactams catalyzed by super nonionic poly(aminophosphazene) and protophosphatrane bases. The super nonionic poly(aminophosphazene) bases appear to mimic catalysis by conventional anionic catalysts, but with the added advantage of the toleration of some degree of moisture. Multinuclear liquid and solid-state NMR experiments were used to probe the structure and proton transfer chemistry of P 4 - t -Bu, one of the most effective lactam ROP poly(aminophosphazene) bases. 31 P magic-angle spinning (MAS) results showed the room-temperature structure of P 4 - t -Bu to be asymmetric and nonprotonated. Variable-temperature 31 P MAS NMR experiments on mixtures of P 4 - t -Bu and ε-caprolactam demonstrated the proton transfer chemistry relevant for ROP at elevated temperature. This was confirmed by 13 C MAS NMR observation of the ε-caprolactam anion in a cross-polarization experiment.