CROSS-LINKED POLY (4-VINYLPYRIDINE) - BRO MINE COMPLEXES AS PRESERVING AGENT FOR FRUIT AND VEGETABLES

With the aim of developing preserving agents (ethylene-removing agents ) for fruit and vegetables, the synthetic conditions and the propertie s of poly (4-vinylpyridine) resins and resin-bromine complexes obtaine d were investigated. Polymerization of 4-vinylpyridine with divinylben zene as a cross linking agent was conducted in aqueous suspension syst ems, in methanol dispersion systems, and in aqueous systems added with some organic solvents. Resins of large granular size with considerabl e strengths were obtained in aqueous suspension systems. However, the specific surface areas of the resins were very small. In methanol disp ersion systems, although resins of large specific areas were obtained, the granules were fragile and troublesome to handle. With the additio n of t-pentyl alcohol and toluene to aqueous dispersion system, porous resins were obtained having sufficient size and strengths of granules for practical use. In this aqueous systems with t-pentyl alcohol and toluene, a part of divinylbenzene could be replaced with styrene and t he resins of lower cost were obtained. 1,2-Dibromoethane was detected when a 4-ethylpyridine-bromine complex as a model for the poly(4-vinyl pyridine)-bromine complex was brought into contact with ethylene gas. Poly(4-vinylpyridine) resins effectively adsorbed 1,2-dibromoethane. T hus, it is suggested that the removal of ethylene by the resin-bromine complex is due to the adsorption of 1,2-dibromoethane, which is produ ced by the addition of bromine in the complex to ethylene. In addition , the rates of ethylene removal by the resin-bromine complexes increas ed as the specific surface areas of the resins increased. This result indicates that the rate-determining step of the reaction is the diffus ion of ethylene into the inside of the poly(4-vinylpyridine)-bromine c omplexes.