Photosensitized polymerization of acrylic monomers. II. Kinetics of polymerization in the presence of oxygen

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.

Aqueous polymerization of methacrylamide initiated by acidified bromate/thiourea redox system

“…Recently two groups of workers 1 -2 d have used these reducing agents with H202 as the oxidant for initiation in the aqueous polymerization of acrylonitrile and suggested a tentative reaction mechanism on the basis of their kinetic studies. DELZENNE et al 3), while conducting a dye (Eosin)-sensitized aqueous photopolymerization of acrylamide in an oxygen atmosphere, concluded that the initiating redox system actually consists of thiourea and H202. The incorporation of an amino-bearing end group in the resultant polymer by redox systems containing thiourea was confirmed by MUKHERJEE et al 4) utilizing dye-partition technique.…”

Effect of coinitiator type on initiation efficiency of two‐component photoinitiator systems based on Eosin

“…For the purpose of this study, Eosin has been selected as the light‐absorbing component, because from among xanthene dyes, Eosin was used most often for photoinitiation of free radical polymerization of monomers. For aqueous solutions of monomers, such as acrylamide or metal acrylates, sodium salts of Eosin (e.g., Eosin Y) were used, which were well soluble in water 19–24. However, most of photocurable monomers used in practice are not soluble in water, while Eosin salts are not soluble in nonpolar media.…”

“…Various compounds, such as amines (e.g., aliphatic amines,25–36 aromatic amines,25, 34, 37 amino‐monomers,38–42 amino‐polymers43), halogenated compounds,44–46 oxime esters,47, 48 iodonium cations,49–54 and other oxidizing or reducing agents,23, 24, 41, 55–61 have been reported in literature as effective coinitiators for Eosin/coinitiator systems. Eosin/amine systems were used most often, either alone or in combination with other coinitiators or UV photoinitiators 29, 42, 62, 63.…”

A Simple and Efficient Model to Determine the Photonic Parameters of a Photopolymerizable Resin Usable in 3D Printing

“…Therefore, there is a trend to use safe photoinitiators. For example, riboflavin (vitamin B2), is a water‐soluble natural dye [13] which has been used as early as 1964 to photopolymerize an aqueous acrylamide under visible light [14] . Subsequently, resins for photocurable films were formulated based on riboflavin and co‐initiators such as amines, [15] amino acids with L‐arginine [16] and tyrosine, [17] thiols with dithiothreitol [18] or proteins [19] .…”