3636 Macromolecules, Vol. 43, No. 8, 2010
Johnson and Cabasso
in the absence of a peroxide (PBIDEP) at 120 °C for 2 h similarly
resulted in precipitation and products with low phosphorus
content.
hydrolysis with formation of monoethyl phosphonyl groups,
(CH3CH2O)(HO)PO.
PBIPOH1. 1H NMR (600 MHz in D2O as Naþ salt), δ (ppm):
7.28-9.03 (br m, Ph-H). 13C NMR (150 MHz in D2O as Naþ
salt), δ (ppm): 114.22-141.49 (br, Ph-C), 154.01 (NH-C=N).
31P NMR (243 MHz in D2O as Naþ salt), δ (ppm): 9.20 - 10.49
(br, (HO)2PO). FTIR (Hþ film form, cm-1): 2800 - 2200 (br,
POH); 1621.8, 1557.4, 1456.5 (s, imidazole ring CdC, CdN);
1157.3 (s, PdO); 1065.2, 994.0, 940.5 (s, POH). Anal. Calcd for
PBIPOH DS (phosphonic acid)=3.1: C, 42.92; H, 2.73; N, 10.01;
P, 17.39. Found: C, 40.29; H, 3.16; N, 8.53; P, 14.90. Ion
exchange capacity (IEC, mequiv of Hþ/g dry polymer), for
DS=3.1, 9.4; for DS=2.4, 8.1; for DS=0.33, 1.9 by titration.
Alkaline hydrolysis: 1H NMR (600 MHz in D2Oas Naþ salt), δ
(ppm): 0.77-1.46 (br, 6H, CH3CH2O), 3.49-3.91 (br, 3.7H,
CH3CH2O), 7.60-8.61 (br m, 3H, Ph-H). 31P NMR (243 MHz
in DMSO-d6), δ (ppm): 11.20, 13.28, 14.18, 14.83, 15.50,
((CH3CH2O)(HO)PO).
When a PBI of higher molecular weight, or greater polydis-
persity, was phosphonylated such as that synthesized in house
(Mn ∼ 29 000; Mw ∼ 73 000) more dilute polymer solutions were
required to prevent gelation. In such cases addition of 10 equiv
of BPO and 120 equiv of DEP to a PBI solution (1.6 wt %) in
DMAc resulted in a DS = 2.3 while use of 60 equiv of DEP
according to the same procedure yielded a DS=2.0. In another
procedure, 5 equiv of BPO and 125 equiv of DEP were added to
a 0.8 wt % PBI solution over 40 min at 120 °C followed by
continued heating for 20 min. Subsequently, 50% by volume of
the solvent was removed by vacuum distillation followed by
addition of 5 equiv of BPO dissolved in DMAc (∼1 g/5 mL).
Heating was maintained an additional 2 h at 130 °C. A PBIPEt
with DS=2.8 was the result.
1
PBIPEt1. H NMR (600 MHz in DMSO-d6), δ (ppm): 1.25
Phosphonylation of Benzimidazole in DMAc Solution. Benzi-
midazole, 3 g (0.03 mol), was dissolved in 120 mL DMAc in a
250 mL three neck round-bottom flask fitted with a magnetic
stir bar, nitrogen inlet nozzle, dropping funnel and condenser.
Under a gentle nitrogen purge, the solution was heated to 100 °C
and 12.2 g (0.05 mol) BPO dissolved in 65 mL (0.58 mol) DEP
was added dropwise to the solution over 30 min. The mixture
was then maintained at 100 °C for 3.5 h. Subsequently, DMAc
and excess DEP were removed by vacuum distillation at 42-
80 °C (8 Torr). The pot residue, a light yellow viscous oil, was
separated into acidic and basic portions by dissolution in
methylene chloride, extraction with 1 M NaOH and 1 M HCl
followed by neutralization and back extraction. From the
NaOH extract was recovered 6.28 g benzoic acid. A flash chro-
matography column (3 ꢀ 35 cm) using silica gel (0.04 - 0.06 mm
particle size, 230-400 mesh) as the stationary phase and ethyl
acetate/methanol (5/1 v/v) as the mobile phase was employed for
separation of the HCl extract. The two major products isolated
were N-(N-methyl acetamidomethyl) benzimidazole (NAB), a
white crystalline solid, 2.73 g (53%) and N-(N-methyl acet-
amidomethyl) benzimidazole diethyl phosphonate (NABP), a
light yellow oil, 1.43 g (17%). NAB and NABP are soluble in
common organic solvents such as methanol, acetone, methylene
chloride, chloroform, ethyl acetate and toluene.
N-(N-Methyl acetamidomethyl) Benzimidazole (NAB, Scheme 2).
1H NMR (600 MHz in DMSO-d6), δ (ppm): 2.02 (s, 3H,
CH3CdO), 2.96 (s, 3H, N(CH3)CH2), 5.76 (s, 2H, N(CH3)CH2),
7.20 (m, 2H, H5,H6), 7.67 (m, 2H, H4,H7), 8.34 (s, 1H,
-N-CHdN-). 13C NMR (150 MHz in DMSO-d6), δ (ppm):
22.07 (CH3CdO), 35.09 (N(CH3)CH2), 55.10 (N(CH3)CH2),
111.45 C7, 119.89 C4, 122.37 C6, 123.15 C5, 133.69 C9, 143.86 C8,
144.98 C2, 171.61 (CH3CdO). FTIR (NaCl, cm-1): 3093.3, 3066.4,
(m, aromatic CH); 2938.8 (m, aliphatic CH), 1662.7 (s, amide
CdO); 1501.5, 1387.3, 1353.7 (m, imidazole ring, CdC, CdN).
Anal. Calcd for C11H13N3O: C, 65.01; H, 6.44; N, 20.67. Found: C,
64.05; H, 6.22; N, 20.09.
(br, 6H, CH3CH2O), 2.04 (br, 0.3H, CH3CdO), 2.83 (br, 0.3H,
N(CH3)CH2), 4.23 (br, 4H, CH3CH2O), 5.80 (br, 0.1H N-
(CH3)CH2), 7.38-8.60 (br m, 2.2H, Ph-H). 13C NMR (150
MHz in DMSO-d6), δ (ppm): 16.27 (CH3CH2O), 22.44
(CH3CdO), 34.75 (N(CH3)CH2), 55.38 (N(CH3)CH2), 62.52
(CH3CH2O), 114.58-151.80 (br, Ph-C), 151.80 (NH-CdN),
169.90 (CH3C=O). 31P NMR (243 MHz in DMSO-d6 at 80 °C),
δ (ppm): 14.26-16.94, ((CH3CH2O)2PO). FTIR (film form,
cm-1): 2992.5, 2938.8, 2905.2 (m, aliphatic CH); 1663.8 (m,
amide CdO); 1450.9, 1394.8 (m, imidazole ring CdC, CdN);
1254.7 (s, PdO); 1052.9, 1027.7 (s, POEt); 974.5 (m, POC).
Anal. Calcd for PBIPEt1 DS(diethyl phosphonyl)=3.1: P, 13.25.
Found: P, 13.79.
PBIPEt2. 1H NMR (600 MHz in DMSO-d6), δ (ppm): 1.04 (br,
6H, CH3CH2O), 2.93 (br, 1.6H, PhCH2P), 3.60-4.07 (br, 5H,
CH3CH2O þ H2O), 7.61-9.88 (br m, 3.6H, Ph-H). 13C NMR
(150 MHz in DMSO-d6), δ (ppm): 16.63 (CH3CH2O), 35.82,
34.93 (minor, PhCH2P), 59.75, 62.48 (CH3CH2O), 112.67-170.91
(br, Ph-C). 31P NMR (243 MHz in DMSO-d6), δ (ppm): 1.63
(0.5P, (OH)2PO), 11.81 (0.9P, (CH3CH2O)(OH)PO), 19.08 (1.3P,
(CH3CH2O)2PdO), 32.57 (1P, (CH3CH2O)2POCH2). FTIR
(film form, cm-1): 2984.3, 2948.7 (s, aliphatic CH); 2627.9,
2496.1, 2360.6 (s, POH); 1636.4, 1475.6, 1446.1, 1400.5 (m,
imidazole ring CdC, CdN); 1202.2 (s, PdO); 1046.7 (s, POEt);
947.5 (m, POC). Anal. Calcd for PBIPEt2 DS(diethyl phospho-
nyl)=2.2: P, 11.23. Found: P, 9.16.
PBIDEP. 1H NMR (300 MHz in DMSO-d6), δ (ppm): 1.20,
1.43 (br, 6.6H, CH3), 3.93, 4.48 (br, 4.6H, CH2), 5.74 (br, 0.5H,
P-H), 7.63, 7.77, 7.93, 8.33, 9.15 (113H, Ph-H). 13C NMR (75
MHz in DMSO-d6), δ (ppm): 115.92 (broad), 122.72, 125.23,
128.02, 130.19, 131.31, 136.49, 139.78 (broad), 151.71(Ph-C),
minor peaks at 25.56, 66.78, 67.46. FTIR (film form, cm-1):
3620-3180 (s, NH); 3066.4 (s, aromatic CH); 1629.1, 1534.3,
1445.2, 1289.1 (m, aromatic and imidazole ring CdC,
CdN); 851.5, 806.9 (m, out of plane bending CH). Anal. Found:
P, < 0.6%.
Hydrolysis of PBIPEt1 (PBIPOH1). PBIPEt1 (19 g) and
200 mL dry DMF were added to a 500 mL three-neck flask
fitted with a magnetic stir bar, nitrogen inlet nozzle, condenser
and a dropping funnel. Under a light nitrogen purge, 41 mL
(0.324 mol) of trimethylsilyl chloride was added dropwise with
stirring followed by the addition of 54 g (0.324 mol) potassium
iodide. The mixture was then heated to 85-90 °C for 90 min.
Afterward deionized water was added to the solution causing
precipitation of the polymer. The polymer precipitate was then
vacuum filtered and washed with deionized water and then with
acetone. After drying, 13.7 g of a brown polymer soluble in
water (pH ∼ 8) but insoluble in water (pH e 5) was obtained.
Strong, pliable, water insoluble films were prepared by solution
casting from aqueous base and ion exchanging with dilute
acid. PBIPEt1 was also hydrolyzed under basic conditions with
hot aqueous sodium hydroxide. 31P NMR indicates partial
N-(N-Methyl acetamidomethyl) Benzimidazole Diethyl Phos-
phonate (NABP, Scheme 2). 1H NMR (600 MHz in DMSO-d6), δ
(ppm): 1.20 (t, 6H, CH3CH2O), 2.03 (s, 3H, CH3CdO), 3.00 (s,
3H, N(CH3)CH2), 4.09 (m, 3.8H, CH3CH2O), 5.80 (s, 2H, N-
(CH3)CH2), 7.35 (td, 1H, H6), 7.64 (dd, 1H, H5), 7.95 (d, 1H, H7),
8.48 (s, 1H, -N-CHdN-). 13C NMR (150 MHz in DMSO-d6),
δ (ppm): 16.66 (CH3CH2O), 22.05 (CH3CdO), 35.21 (N-
(CH3)CH2), 55.32 (N(CH3)CH2), 62.10 (CH3CH2O), 116.13 C7,
119.58 C4, 122.60 C6, 127.53 C5, 133.90 C8, 144.08 C9, 146.08 C2,
171.78 (CH3CdO). 31P NMR (243 MHz in DMSO-d6), δ (ppm):
18.85 ((CH3CH2O)2PO). FTIR (NaCl, cm-1): 3070, (w, aromatic
CH); 3000, 2950, 2900, (m, aliphatic CH), 1653.7 (s, amide CdO);
1489.6, 1420.9, 1385.1, 1349.3 (m, imidazole ring, CdC, CdN);
1247.8 (s, PdO); 1056.7.1, 1026.9 (s, POEt); 967.2 (m, POC).
Anal. Calcd for C15H22N3O4P: C, 53.09; H, 6.54; N, 12.38; P, 9.13.
Found: C, 53.99; H, 6.26; N, 11.93; P, 8.47.