Synthesis and Mechanism of PBI Phosphonate, Poly[2,2′-(-m-phenylene)-5,5′-Bibenzimidazole Phosphonate Ester], and its Polyphosphonic Acid Derivatives

Abstract

Polybenzimidazole diethyl phosphonates (PBIP Et ) of high phosphorus content (as high as ∼13%) have been synthesized by reacting poly[2,2 0 -(m-phenylene)-5,5 0 -bibenzimidazole] (PBI) with diethyl phosphite and a peroxide, in N,N-dimethylacetamide solution, via a free radical mechanism. The phosphonate ester groups are linked directly to the aromatic backbone thus establishing a strong -(Od)P-Phbond. The highly phosphonylated products dissolve in lower alcohols and the corresponding polyphosphonic acids (PBIP OH ) dissolve in aqueous sodium hydroxide (pH ∼ 7-8); membranes composed of either polymer are readily prepared. PBIP OH displayed high thermal stability as well as charge densities as high as ∼9 mequiv of H þ /g. Model compounds benzimidazole and 2,2 0 -diphenyl-5,5 0 -bibenzimidazole have been phosphonylated under similar conditions in order to resolve phosphonylation mechanism, and some aspects of a rather complicated oxidative substitution. Benzoic acid is a byproduct of reactions involving benzoyl peroxide supporting a mechanism that involves breakdown of the peroxide into radicals followed by reaction with the phosphite ester and subsequent attack of phosphorus centered radicals on an aromatic ring. In the case of PBI, phosphonylation appears to occur preferentially at the C 4 and C 7 positions of the benzimidazole rings (on the benzene ring adjacent to the fusion points) as well as on the m-phenylene rings ortho-to the linkage with benzimidazole. The observed substitution pattern is likely controlled by the resonance stability of the radical adduct.

Iron-Catalyzed N-Alkylation of Azoles via Cleavage of an sp3C–H Bond Adjacent to a Nitrogen Atom

“…N-((1H-Benzo[d]imidazol-1-yl)methyl)-N-methylacetamide (3a). 13 Light yellow oil (97 mg, 96%): 1 H NMR (400 MHz, CDCl 3 ) δ 7.89 (s, 1H), 7.71 (d, J = 7.2 Hz, 1H), 7.50 (d, J = 8.0 Hz, 1H), 7.21 (t, J = 3.8 Hz, 2H), 5.63 (s, 2H), 2.91 (s, 3H), 2.03 (s, 3H); 13 C NMR (100 MHz, CDCl 3 ) δ 171. 4, 143.5, 143.4, 133.1, 123.5, 122.6, 120.1, 110.3, 55.0, 35.0, 21.7; HRMS (TOF MS EI + ) m/z calcd for C 11 H 13 N 3 O 203.1059, found 203.1061.…”

Phosphonated polyimides: Enhancement of proton conductivity at high temperatures and low humidity

“…In addition, amphoteric character of phosphonated polymers results in their ability to conduct protons even under anhydrous conditions thru the Grotthuss mechanism [35,36]. Practically, however, the phosphonated polymer electrolytes are not well studied due to relatively limited synthetic approaches and their moderate conductivity which necessitates high degree of phosphonation to attain sufficient conductivity [37][38][39][40][41].…”

Poly(arylene benzimidazole)s as novel high-performance polymers

“…To address the above-mentioned problems, much research has been dedicated to understanding the structural variation of PBI polymers to control and improve their properties. [13][14][15][16][17][18] One such effort involves the substitution of the potentially reactive N-H site in benzimidazole by functional groups, 7,[19][20][21][22][23][24] thereby enabling a C-N coupling reaction with activated halides at the appropriate temperature. [25][26][27] In addition, to improve the processability of PBI, the ether, sulfone and other functional groups in PBI polymers can be modified to lower the thermo-oxidative stability but increase the solubility and flexibility of PBI, which allows further processing and modification (cross-linking and sulfonation to high ion-exchange capacity) of PBI and enables the production of films with good mechanical properties.…”