No abstract

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.

By polymerization of vinyl monomers in the visible light in the presence of dyes (eosin, safranine, acridine orange), ascorbic acid, and oxygen, following the method of Oster, the dye is incorporated as a leuco form into the polymer molecule. In the synthesis of N(eosin) polyvinylamine, one tenth of the amino groups carries a coloured group. This polymer was used for the synthesis of graft polymers with acrylamide, acrylic acid, acrylonitrile, and styrene. The graft polymers were isolated by fractionation; the yield is particularly high with acrylamide and acrylic acid. The per cent contents in the second monomer were 41 (acrylamide), 38 (acrylic acid), 14 (acrylonitrile), and 36 (styrene). The method also makes possible the synthesis of polymers with branches of different chemical structure by successive photopolymerizations of two different monomers, e.g., acrylamide and acrylic acid. Similarly, starting from ω‐N‐(eosin) polymethyl methacrylate, block polymers were synthesized with styrene and acrylamide; the contents in the second monomer was 40 and 79%, respectively. By hydrolysis experiments it was demonstrated that the leuco dye group constitutes the intermediate link in these block polymers between the two monomer sequences.

The photopolymerization of acrylamide in aqueous solution can be sensitized by various dye–reducing agent systems. The reaction is initiated by free radicals produced during the decomposition, in the presence of reducing agents, of hydrogen peroxide. This substance is formed during the reoxidation reaction by the oxygen present in the solution of the leuco derivative or the semiquinone which are produced in the photoreduction of the dyes. The formation of hydrogen peroxide during the photoreduction of dyes in the presence of oxygen has been demonstrated polarographically for the following systems: tetrabromofluorescein (eosin), 3,6‐diaminoacridine (acriflavin), 3,6‐bis(dimethylamino)acridine (acridine orange) as dyes and l(+)‐ascorbic acid or thiourea as reducing agents.

SynopsisPhotosensitive polymers containing arylazido groups were obtained by interfacial polycondensation of azido-substituted acid chlorides with diols and diamines. The light sensitivity was studied with the polyester synthesized by condensation of m-azidoisophtaloylchloride and 4,4 '-dihydroxydiphenylpropane. The qualitative determination of the sensitivity on a relative scale was based on a standardized technique of irradiation of coated layers. The study of the influence of the degree of substitution on the photosensitivity showed a threshold substitution value indicating some loss of reticulating points at lower degrees of substitution and a levelling of the sensitivity about 50% substitution. The addition of sensitizers of the carbonyl type was able to increase the sensitivity of the arylazido polycondensates. An optical sensitization by triplet-triplet energy transfer was put forward a s a possible explanation. Measurements of the photolysis rate and of the crosslinking threshold decomposition value allowed us to check the validity of the hypothesis of a decreased crosslinking capacity due to side reaction of the imido intermediates.