New initiators for the ring-opening thermal polymerization of hexachlorocyclotriphosphazene: synthesis of linear poly(dichlorophosphazene) in high yields

Abstract

Ring-opening thermal polymerization of hexachlorocyclotriphosphazene (N₃P₃C₆)has been investigated at 250°C and at 1.333-Pa pressure using chlorocyclotriphosphazenes N₃P₃C1₅(N=PPh₃) and N₃P₃Cl_6-n(NMe₂) (n = 2-4), salt hydrates, triphenylphosphine, and benzoic acid as initiators. The linear poly (dich1orophosphazene) products are phenoxylated, and the phenoxy polymers are characterized by gel permeation chromatography and dilute solution viscometry. Among the various initiators investigated, CaS0₄·2H₂0 brings about a high conversion (>60%) of N₃P₃Cl₆ to the linear [NPC1₂]n polymer which possesses a high molecular weight (>5 × l0⁶). The rationale for the choice of the initiators and possible mechanism(s) of polymerization is discussed. Several mixed substituent polymers, [NP(OPh)_x(OC₆H₄Me-p)_2-x]_n and [NP(OPh)_x(OCH₂CF₃)_2-x]_n have been prepared and their thermal properties evaluated.