Fast Synthesis, Using Microwave Induction Heating in Ionic Liquid and Characterization of Optically Active Aromatic Polyamides

Abstract

A simple pathway for the preparation of optically active aromatic polyamides (PAs) is reported. A fairly inexpensive and readily accessible molten ionic liquid, tetrabutylammonium bromide (TBAB) was used for the synthesis of polymers. PAs were synthesized from polycondensation of (2S)-5-[4-(4-methyl-2-phthalimidyl pentanoylamino)benzoylamino]isophthalic acid with various commercially available diisocyanates in N-methylpyrrolidone (NMP) as common organic solvent and molten TBAB as a green medium with or without dibutyltin dilaurate as a catalyst under microwave irradiation. Polycondensation process in TBAB is safe and green since toxic and volatile organic solvent such as NMP was eliminated. Various PAs were obtained with high yields and moderate inherent viscosities in the ranging from 0.26 to 0.91 dL/g. The obtained polymers were characterized by FT IR, specific rotation measurements, ¹H NMR, elemental and thermogravimetric analysis techniques and differential scanning calorimetry.

Keywords:

• Optically active polymers
• green chemistry
• aromatic polyamide
• ionic liquid
• microwave irradiation
• thermogravimetric analysis

Acknowledgments

We wish to express our gratitude to the Research Affairs Division Isfahan University of Technology (IUT), Isfahan, for partial financial support. Further financial support from the National Elite Foundation (NEF) and Center of Excellency in Sensors and Green Chemistry Research (IUT) is gratefully acknowledged. We also extend our thanks to Mr. Mehdi Taghavi and Mohammad Dinari for their voluble assistants.

Notes

^b Measured without filter.

^c This polymer was precipitated in MeOH.

^d These polymers were precipitated in MeOH/Water.

^e W = White;

^f Y = Yellow.

^b Measured without filter.

^c These polymers were percipitated in MeOH/Water.

^d This polymer was precipitated in MeOH.

^e Y = Yellow.

^f B = Brown.

^g W = White.

^a Temperature at which 5% wt loss was recorded by TGA at a heating rate of 10°C/min in a nitrogen atmosphere.

^b Temperature at which 10% wt loss was recorded by TGA at a heating rate of 10°C/min in a nitrogen atmosphere.

^c Percentage weight of material left undecomposed after TGA analysis at maximum temperature 800°C in a nitrogen atmosphere.

^d Glass-transition temperature recorded at a heating rate of 20°C/min in a nitrogen atmosphere.

^e Limiting oxygen index (LOI) evaluating at char yield at 800°C.