Cationic homo- and copolymerization of fluorophosphoranimines as an ambient temperature synthetic route to poly(fluorophosphazenes), [N=PF(R)]_n, with controlled architectures

The PCl₅-induced polymerization of the fluorophosphoranimine PhF₂P=NSiMe₃ at ambient temperatures (35 °C) yields the poly(fluorophosphazene) [N-PF(Ph)]_n This THF-soluble product was treated with an excess of sodium triflouroethoxide in refluxing dioxane to replace the fluorine atoms by trifluoroethoxy groups and generate the known hydrolytically stable polymer [N=PPh(OCH₂CF₃)]_n. The molecular weights in this system can be controlled by variation of the monomer to initiator ratios, and polydispersities for [N=PPh(OCH₂CF₃)]_n are in the range of 1.05-1.32. In order to explore the synthetic utility of [N=PF(Ph)]_n, the polymer was treated with Grignard or alkyllithium reagents such as MeLi, n-BuLi, or p-tolylmagnesium bromide to produce the poly(organophosphazenes) [N-PPh(R)]_n (R = Me, n-Bu, p-tolyl). Complete replacement of the fluorine atoms using alkyl/aryllithium reagents induced a significant decline in molecular weights However, treatment of [N=PF(Ph)]_n with a 0.5 molar equiv of MeLi at -78 °C, followed by replacement of the remaining fluorine atoms with NaOCH₂CF₃ in refluxing dioxane, produced the mixed-substituent polyphosphazene {[N-PPh(OCH₂CF₃)_0.5(Me)_0.5] _y} with M_a = 2.4 × 10⁴ (PDI = 1.10) The phosphoranimine PhF₂P=NSiMe₃ also reacts at 35 °C with "living" poly-(dichlorophosphazene). (N=PCl₂)_n, to produce the block copolymer {[N=PCl₂]_n[N=PPh(F)]_m}. Halogen replaoement by NaOCH₂CF₃ in refluxing dioxane produced the known hydrolytically stable block copolymer {[N=P(OCH₂CF₃)₂]_n[N=PPh(OCH ₂CF₃)]_m} with W_n = 4.5 × 10⁴ (PDI = 1.30).