Synthesis of High Molecular Weight Poly(p-benzamide)s

Michael Badoux,Andreas F M Kilbinger

doi:10.1021/acs.macromol.7b00515

Abstract

The polymerization of aromatic para-amino acid ester derivatives was studied using model compounds. Mechanistic and kinetic experiments led to the discovery of some side reactions. Finally, high molecular weight poly(p-benzamide)s were synthesized and characterized. The use of highly reactive pentafluorophenol ester lead to polymers up to molecular weights of around 50 000 Da. Poly(benzamides) carrying both N-alkyl or N-benzyl groups on the amine could be polymerized to high molecular weight.

Highlights

Over the past decade, many efforts have been made to synthesize high molecular weight aromatic polyamides
Hydrolysis of the methyl ester gave the free acid (4, 91%) and the reduction of the nitro group under hydrogen pressure in the presence of palladium lead to the successful synthesis of the doubly substituted aromatic amino acid (5, 96%)
The direct polymerization of primary amino acids such as phenyl 4aminobenzoate following the procedure described by Yokozawa and co-workers is difficult to carry out as the secondary amide formed during the polymerization is more acidic than the primary amine of the monomer

Summary

■ INTRODUCTION

Many efforts have been made to synthesize high molecular weight aromatic polyamides (aramides). Allyl bromide (0.326 mL, 3.77 mmol) was added dropwise to a stirring solution of 4-amino-2-((2-ethylhexyl)oxy)benzoic acid (9) (1 g, 3.77 mmol) in DCM (7.54 mL, 0.5 M) with DIPEA (1 mL, 5.73 mmol) at 0 °C. 4-Amino-2-((2-ethylhexyl)oxy)benzoic acid (9) (1 g, 3.77 mmol) and 2,4-dimethoxybenzaldehyde (0.689 g, 4.15 mmol) were dissolved in DCM (6.28 mL, 0.5 M) and acetic acid (1.25 mL) and stirred for 1 h at room temperature. The product was purified by column chromatography using ethyl acetate/hexane (1:20) as eluent to obtain product M10 as a transparent oil (0.456 g, 1.09 mmol, 83%).1H NMR (400 MHz, chloroform-d), δ, ppm: 0.75−1.13 (m, 6 H) 1.21−1.54 (m, 8 H) 1.54−1.75 (m, 1 H) 3.14 (t, J = 5.9 Hz, 2 H) 4.18−4.77 (m, 1 H) 6.34−6.92 (m, 2 H) 7.76−8.32 (m, 2 H).

■ RESULTS AND DISCUSSION

■ CONCLUSIONS

■ REFERENCES