Synthesis and characterization of poly(amide-imide)s bearing a S-valine moiety in molten ionic liquid.
A study has been conducted to synthesize highly organosoluble and optically active poly(amide-imide)s via direct solution polycondensation of different aliphatic and aromatic diisocyanates with a chiral diacid monomer in the presence of molten tetrabutylammonium bromide (TBuAmBr) as a molten ionic liquid, and was compared with polymerization in traditional solvents like N-methyl-2-pyrrolidone (NMP). The step-growth polymerization of N-trimellitylimido-S-valine (1) as an optically active monomer with 4,4′-methylenebis(phenyl isocyanate) (MDI) (2a) was carried out by four different methods in the presence of pyridine (Py), dibutyltin dilaurate (DBTDL), triethylamine (TEA) as a catalyst and without catalyst, respectively. In these solutions polycondensations amino acid was used as chiral inducing agent. The optimized method of MDI (2a) was used for the polymerization of hexamethylene diisocyanate (HDI) (2b), isophorone diisocyanate (IPDI) (2c) and tolylene-2,4-diisocyanate (TDI) (2d). The resulting polymers have inherent viscosities in the range of 0.15–0.87 dl/g and were characterized with FT-IR, 1H-NMR, elemental and thermogravimetric analysis techniques. In comparison with conventional solvents, this approach exhibited smoothly higher inherent viscosities and comparative yields and thermal stability. This process is safe and green since toxic and volatile organic solvents such as NMP were eliminated. These polymers are optically active, thermally stable and soluble in amide-type solvents.