The kinetics of the photopolymerization of acrylamide and methacrylic acid in aqueous and semi‐organic solutions have been examined; the initiating redox system used in the presence of oxygen were eosin‐thiourea, eosin‐1‐ascorbic acid, or in some cases riboflavine. The rates of photopolymerization were determined by measuring the thermal rise of the reaction cell using a thermistor technique. In aqueous and in semi‐organic solutions, the rate is proportional to the square of the monomer concentration in both cases. Below a critical concentration of sensitizer the rate of polymerization of monomers is proportional to the square root of sensitizer concentration (acrylamide in the presence of riboflavine, methacrylic acid in the presence of eosin‐ascorbic acid); above it, the rate becomes inversely proportional to the square root of the sensitizer concentration. With respect to the reducing agent concentration, the exponent for thiourea is located between 0.5 and 1 in the case of acrylamide and 0.5 for methacrylic acid. Finally with respect to the oxygen concentration the rates are proportional to the square root of its concentration, at least below a given oxygen‐concentration where the induction period becomes predominant. These results are interpreted assuring a participation of the monomer in the initiation step, and a low initiation efficiency of the primary radicals (cage recombination). A kinetic scheme is presented and the experimental results discussed on the basis of it.

SynopsisOrdered heterocycle copolymers of high thermal stability were prepared from aromatic dianhydrides reacted with aromatic diamines containing preformed benzoxazole or benzothiazole units. These ordered benzoxazole-imide and benzothiazole-imide copolymers were prepared in the form of their soluble precursor polyamic-acids, which, after fabrication to desired shapes, were converted to the thermally stable polymer. In general, these polymers are more resistant to air oxidation at elevated temperatures than are simple aromatic polyimides, and their thermooxidative stability is equal to or greater than that reported for benzoxazole or benzothiazole homopolymers. Unlike the o-hydroxyamide precursors to simple polybenzoxazoles, the amic acid precursors to benzoxazole-imide ordered copolymers do not require temperatures above 300°C to complete ring closure nor inert atmospheres to prevent polymer degradation during ring formation. Excellent self-supporting films and film coatings for metals were prepared. Selected compositions were readily spun to excellent fiber.

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Fibers of benzoxazole–imide ordered copolymers were prepared by cyclodehydrating the amide–phenol units of precursor polyamide–o‐hydroxyimide fibers at 375°C in nitrogen. The precursor polyamide–o‐hydroxyimides were obtained by the reaction of 3,3′‐dihydroxybenzidine with diacid chlorides containing preformed imide rings. The benzoxazole–imide fibers are very thermally stable, especially with respect to retention of tensile properties after heat aging in air. For example, the benzoxazole–imide fibers after heating aging in air for 35 days retained 75% or more of their original tenacities and 50% or more of their original elongations to break. The original fibers did not have high tenacities, probably because of the rather extreme thermal treatment required to cyclodehydrate the amide–phenol units of the precursor fiber. The ultraviolet light stability of one benzoxazole–imide fiber was outstanding for a fiber of the polyheterocycle type: there was no loss in strength or elongation after 140 hr of exposure in a Fade‐Ometer. Fibers of ordered amide–imide polymers based on the same imide‐containing diacid chlorides used for the benzoxazole–imide polymers were also prepared. They were substantially less thermally stable than their benzoxazole–imide fiber counterparts, as expected.

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