N-ALKYLATION AND HOFMANN ELIMINATION FROM THERMAL-DECOMPOSITION OF R4N+ SALTS OF AROMATIC POLYAMIDE POLYANIONS - SYNTHESIS AND STEREOCHEMISTRY OF N-ALKYLATED AROMATIC POLYAMIDES

The reaction of aromatic polyamides such as poly(p-phenyleneterephthalamide) (PPTA) with (n-Bu)4N+-OH or Et4N+-OH gives dimethyl sulfoxide (DMSO) soluble polyanions as the (n-Bu)4N+ or Et4N+ salts derived from deprotonation of the amide hydrogen. The n(R4N+)PPTA(n-) salts thermally decompose by Hofmann elimination to yield neutral PPTA, olefin, and NR3. Dissolving PPTA by deprotonation and thermally decomposing the R4N+ salt can be used to process the polymer. Films cast from DMSO solutions of nR4N+PPTA(n-) convert from polyanion to a PPTA film when heated to about 200-degrees-C, removing solvent and volatile byproducts, and leaving a crisp PPTA film. Model studies show that N-alkylation competes with the Hofmann elimination of nR4N+PPTA(n-). Whereas n(n-Bu)4N+PPTA(n-) undergoes extensive N-butylation, nEt4N+PPTA(n-) shows only trace amounts (< 1%) of ethylated product. N-Alkylation changes the stereochemistry of the amide bond from trans to cis, causing the N-alkylated PPTA derivatives to behave as a random coil rather than a rigid rod in solution. N-Alkylation comprises the mechanical properties of PPTA films.