No abstract

The reaction of aromatic polyamides such as poly(p-phenylene terephthalamide) (PPTA) with a variety of strong bases to yield dimethyl sulfoxide (DMSO) soluble polyanions has been explored.At least 60% of the amide groups must be deprotonated to give soluble polyanions of PPTA, Little loss of molecular weight was observed under 40 °C. Solution viscosity was highly dependent on the cation, with potassium giving lower viscosity solutions than sodium. The viscosity of the PPTA solutions increased with the degree of deprotonation, suggesting an increase in chain stiffness. Addition of proton donors, such as methanol, to the reaction of base with the aromatic polyamide in DMSO significantly enhanced the rate of polymer dissolution and gave higher solubilities and lower solution viscosities. Deprotonation of dibenzoyl-p-phenylenediamine was studied as a model compound for PPTA, confirming the results from the polymer. A single-crystal X-ray diffraction study of the model compound as its dianion revealed a short C-N bond and a long C-0 bond in the amide groups indicative of increased conjugation through the backbone chain. Properties of films and fibers from processing the isotropic anion solutions are also described.

A facile method was developed for crosslinking stiff chain polymer fibers such as Kevlar® and polybenzobisthiazoles (PBZT). The method is based on thermolysis of active aryl halides contained in the polymer unit and coupling of the free radicals formed. The method worked well for the PBZT polymers and improvements in fiber single filament recoil stress and shear modulus were demonstrated. In the case of the polyamides chain cleavage apparently accompanied the crosslinking, limiting improvement in the recoil stress test. The mode of degradation appeared to be rearrangement of the amide linkage to isocyanate.

Thirteen aliphatic and aromatic polyhydrazides have been converted as bulk polymer by a unique polymer by a unique polymer post reaction into high molecular weight poly(1,3,4‐oxadiazoles). This reaction proceeds by thermal cyclodehydration at 170–280°C. with elimination of water. The resulting poly(1,3,4‐oxadiazoles) have been characterized by microanalysis, inherent viscosity, x‐ray diffraction patterns, and by infrared and ultraviolet absorption spectra. Films could be pressed from the melt of polyoxadiazoles melting below 350°C., while very high melting or infusible aromatic polyoxadiazoles could not be manufactures into films and fibers by conventional means. Such polymers are extremely thermally and oxidatively stable and decompose between 450 and 500°C.