Preparation of starch 2‐hydroxy‐3‐mercaptopropyl ethers and their use in graft polymerizations

摘要

AbstractStarch 2‐hydroxy‐3‐mercaptopropyl ethers of degree of substitution (DS) up to 0.34 were prepared as follows: starch was reacted with epichlorohydrin to give 3‐chloro‐2‐hydroxypropyl ethers which were treated with thiosulfate to displace chloride ion followed by reduction of the resulting thiolsulfonates with sodium borohydride. These mercapto ethers formed graft copolymers with acrylonitrile, styrene, acrylic acid, and dimethylaminoethyl methacrylate (DMAEMA) under hydrogen peroxide initiation. The resulting graft copolymers, after treatment with sodium borohydride to regenerate thiol groups from disulfides formed by peroxide oxidation, could then be reacted with additional monomer and peroxide to increase add‐on of the synthetic moiety. Graft copolymers containing about 60 polyacrylonitrile or 70 polystyrene were thus obtained. Repeated graftings were carried out successfully with two, three, or four different monomers added sequentially. Hydrophobic monomers graft polymerized more readily onto graft copolymers containing hydrophobic chains, whereas hydrophilic monomers graft polymerized more readily onto hydrophilic graft copolymers. Graft copolymers prepared from acrylic acid and DMAEMA precipitated near the isoelectric point upon neutralizing their acidic or ba