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synopsisThe efficacy of oxidatively crosslinked starch xanthate for improving web and drystrength properties of paper prompted the present study of an alternative, interpolymeric crosslinking procedure. Sodium starch xanthate of degrees of substitution 0.05-0.25 was reacted with a commercial paper additive (a polyamide-polyamine-epichlorohydrin wet-strength resin) which was found to contain 3-hydroxyazetidinium chloride, epoxypropyl, and chlorohydrin groups (3: 1: 1) to give an interpolymer crosslinked by both ionic and covalent bonds. Model systems, in conjunction with nuclear magnetic resonance, infrared, and ultraviolet spectral data, served to elucidate reaction mechanisms and structures of the interpolymer and the commercial resin. Reaction conditions that favored formation of either ionic (polysalt) or covalent (xanthate ester) crosslinks were investigated. In preliminary evaluations, incorporation of the interpolymer into paper handsheets resulted in excellent wet-and dry-strength improvements.