Some observations in the aqueous and emulsion polymerizations of common vinyl monomers initiated by sodium metabisulfite (Na2S2O5) at 50°C

Abstract

SynopsisAnalytical grade sodium metabisulfite (NazS205) has been found to initiate the polymerizations of methyl methacrylate (MMA) and ethyl methacrylate (EMA) in the aqueous media in the presence and absence of detergents, and of styrene in the presence of detergents only, but it fails to initiate the polymerization of methylacrylate (MA) at low concentrations of the initiator and of acrylonitrile (AN) in the absence of cationic detergent micelles. If a mixture of AN (2.0%, v/v) and metabisulfite (l.60%, w/v) is kept for 16 h at 5OoC in the presence of nitrogen, no polymerization occurs, but if a little ferric chloride (0.001%, w/v) is added to this mixture in nitrogen atmosphere, the initiation of AN polymerization is found to occur. MA can be polymerized partly by adding metabisulfite to an aqueous solution of MA and a cationic detergent (above CMC) in the presence and absence of air. Very little polymer is found under similar conditions with AN. No polymerizations were found to occur with any of the above-mentioned monomers if hydroquinone was present in the system. In the Na2S205-MMA and Na2S205-EMA systems, the average rates of the aqueous polymerizations were found to decrease with the increase of the initiator concentrations (from 1.316 X to 2.63 X lo-' m n ) at 50°C in the presence of nitrogen, and to be approximately inversely proportional to the square root of the initiator concentrations. It is suggested that the bisulfite (produced by the reaction of S20;-ions with water) adds to vinyl monomers as well as initiating polymerization reactions by the reduction activation of the monomers in the presence of nitrogen. The presence of bulky groups such as methyl, phenyl, etc., at the 0-position of the ethylenic double bond of the monomer, probably prevents or slows down the bisulfite addition reactions due to the steric hindrance, and so the polymerization reactions will predominate in the system of MMA, EMA, and styrene-like monomers. The complex species formed due to the interactions of the cetyltrimethyl ammonium bromide (CTAB) micelles and free CTAB cations with HSO; and Sz0;-ions initiate the polymerizations of MA and of AN in the presence of nitrogen or air. Cationic detergent micelles protect the monomers from the direct attack of the HSO;/S20;-ions.

Bisulfite-initiated crosslinking of gelatin methacryloyl hydrogels for embedded 3D bioprinting

“…On the other hand, these salts are unable to initiate the polymerization other monomers, which do not contain methacrylate groups, such as methyl acrylate, vinyl acetate. Due to their monomer selectivity, they are not widely used as initiators [14][15][16][17][18][19]. The initiation mechanism of bisulfite is based on radical formation resembling the bisulfite-persulfate redox system [14].…”