On the reaction of catenapoly(diphenoxy‐λ⁵‐phosphazene) with sulfur trioxide

Abstract

The reaction of catenapoly(diphen0xy-A'-phosphazene) (1) with SO, in 1,2-dichloroethane at 15 "C, applying a mole ratio m = [SO,]/[-P(OC,H,),N-.]G 1 ,O and subsequent quenching with water, leads to catenapoly(diphenoxy-A'-phosphazene-co-diphenoxy-A'-phosphazenium hydrogen sulfate) (2) containing up to 57% protonated nitrogen. At rn > 1,0 C-sulfonation occurs, resulting in the formation of water-soluble catenapoly[diphenoxy-A'-phosphazene-codiphenoxy-A'-phosphazenium hydrogen sulfate-co-bis(su1fophenoxy)-A'-phosphazenium hydrogen sulfate] (3). The latter can be converted into catenapoly[diphenoxy-As-phosphazeneco-bis(sulfophenoxy)-A5-phosphazene] (4 b) by treatment with alkali and subsequent percolating through a cation exchange resin. Analytical results show that C-sulfonation is preceded by the formation of a polymer-SO, donor-acceptor complex. #N{ R = OR', OAr: NR'R'', aryl, alkyl. A "Polyphosphazenes containing strong acid functions are not known. Yet, enriching the phosphazene matrix with additional inorganic elements in acid form is likely to be an efficient mean to prepare new hydrophilic or water-soluble polymers and to extend the potential uses4) of poly(15-phosphazene)~. Catenapoly(diphenoxy-Is-phosphazene) (1) appeared mostly suitable for the purpose; the pendent aromatic ring being a site where C-sulfonic functions can be readily attached.The C-sulfonation of 1 should offer some challenge. The Is-phosphazene skeleton is inert to most chemical reactions, but it has been reported to undergo some degradation in the presence of conc. sulfuric acid5). The use of this and other sulfonating agents (i. e. oleum, chlorosulfonic acid and sulfur trioxide in complexing solvents), which require heating to react4s6), was, therefore, discarded. Free SO, in uncomplexing solvents allows to operate at or below room temperature and has been used efficiently in the sulfonation of aromatic compounds7). However, 1 contains a potential electron-donor site (i. e. nitrogen in the polymer backbone), in addition to the phenoxy groups. Similarly to the sulfonation of pyridine*), complexation of SO, at the nitrogen site could limit the reactivity of SO, and require high temperature to achieve C-sulfonation. On the other hand, Allcock et al.9) showed that skeletal electrophilic attack (i. e. alkylation) in 15-phosphazenes may be hindered by pendent substituents. A further complication in sulfonation is the possible formation of intermolecular sulfone link^^.^). This fact, in the case of polymers, yields intractable, cross-linked, non-melting materials which are insoluble in all solvents.The herewith reported sulfonation of 1 with SO, in 1,2-dichloroethane was carried out to investigate these aspects and to yield new water-soluble acid catenapoly(A5phosphazene)s.

Polyphosphazene membranes. III. Solid-state characterization and properties of sulfonated poly[bis(3-methylphenoxy)phosphazene]

“…From a comparison of the SO 3 /POP mer molar ratios and the mol % C-sulfonation in Table I, the reaction yield for the SO 3 Ϫ site creation was deter- mined (noting that there are two methylphenoxy groups per mer) and varied from a low of 1.6% at SO 3 /POP ϭ 0.64 to 44% at a SO 3 /POP ratio of 1.6. These results are in agreement with the work of Montoneri et al 11,12 who found that backbone nitrogens in polyphosphazenes were attacked first by SO 3 and are also consistent with our previous sulfonation studies with poly[(3-methylphenoxy)(phenoxy)phosphazene], 4 where no IEC was detected for a SO 3 /POP ratio Յ0.8.…”

“…The sulfonation of aryloxy-and (arylamino)phosphazenes via reaction with sulfuric acid was studied by Allcock and Fitzpatrick 10 while the reaction of (aryloxy)polyphosphazenes with sulfur trioxide was studied by Montoneri and coworkers. 11,12 During the initial stages of SO 3 addition, Montoneri et al found no C-sulfonation, but, rather, the formation of a 'N3 SO 3 complex. When the SO 3 /mer molar ratio was Ն 1, C-sulfonation was observed.…”

The synthesis of functional polyphosphazenes and their surfaces

“…The difference here is that an average of 30 000 of these reactions are carried out on each molecule. 41,42 The p-methyl groups of NP(OC 6 H 4 CH 3 ) 2 ]n can be oxidized to COOH groups with permanganate. 43 45 The challenge with reactions of this type is to complete the functionalization without inducing cleavage of the inorganic backbone.…”

Proton-Exchange Membranes Based on Sulfonated Polymers

“…7). Difficulties are associated with preparation of the water-insoluble polymers [40][41][42][43][44][45] , and conditioning their hydrophile / hydrophobic properties. Waterinsoluble membranes based on polyphosphazenes can be prepared by crosslinking, introduction of alkyl groups to the aromatic ring of the side chains or by varying the degree of sulfonation of the polymer 46 .…”