Magnetic recording medium containing a polyurethane copolymer with a free radically polymerized polymer segment grafted to the polyurethane through a sulfur atom

摘要

The invention relates to a sulfonated, thiol, and hydroxy- functional polyurethane polymer which comprises: (i) a polyurethane backbone; (ii) at least one SO.sub.3 M group pendant from the polyurethane backbone, wherein the polyurethane backbone has an SO.sub.3 M equivalent weight of from about 2,000 to about 100,000, and wherein M is selected from the group consisting of H.sup.+, NR.sub.4.sup.+ wherein R can be H.sup.+ or an alkyl group, Li.sup.+, Na.sup.+, K.sup.+, and mixtures thereof; (iii) at least two crosslinkable hydroxy groups pendant from the polyurethane backbone, wherein the polyurethane backbone has a hydroxy equivalent weight of from about 500 to about 50,000; and (iv) at least one --SH group pendant from the polyurethane backbone. The invention also relates to vinyl/polyurethane copolymers made therewith which are particularly useful as binders in magnetic recording media and a method of making the copolymers. The invention also relates to certain nonsulfonated thiol and hydroxy functional polyurethane graft copolymers and dispersions made therewith.