Cationic Homo- and Copolymerization of Fluorophosphoranimines as an Ambient Temperature Synthetic Route to Poly(fluorophosphazenes), [NPF(R)]n, with Controlled Architectures

The PCl 5 -induced polymerization of the fluorophosphoranimine PhF 2 P NSiMe 3 at ambient temperatures (35 °C) yields the poly(fluorophosphazene) [N PF(Ph)] n . This THF-soluble product was treated with an excess of sodium trifluoroethoxide in refluxing dioxane to replace the fluorine atoms by trifluoroethoxy groups and generate the known hydrolytically stable polymer [N PPh(OCH 2 CF 3 )] n . The molecular weights in this system can be controlled by variation of the monomer to initiator ratios, and polydispersities for [N PPh(OCH 2 CF 3 )] 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 NaOCH 2 CF 3 in refluxing dioxane, produced the mixed-substituent polyphosphazene {[N PPh(OCH 2 CF 3 ) 0.5 (Me) 0.5 ] y } with M n = 2.4 × 10 4 (PDI = 1.10). The phosphoranimine PhF 2 P NSiMe 3 also reacts at 35 °C with “living” poly(dichlorophosphazene), (N PCl 2 ) n, to produce the block copolymer {[N PCl 2 ] n [N PPh(F)] m }. Halogen replacement by NaOCH 2 CF 3 in refluxing dioxane produced the known hydrolytically stable block copolymer {[N P(OCH 2 CF 3 ) 2 ] n [N PPh(OCH 2 CF 3 )] m } with M n = 4.5 × 10 4 (PDI = 1.30).