Particularly preferred crosslinked resins of this invention may be represented by the formulas ##STR12## wherein X is hydrogen or (C1 -C6) alkyl, such as methyl or ethyl; and wherein the initial linear polymer is in the form of uniform PVBC beads which are thermally lightly crosslinked (stabilized) so that they will not dissolve when they are swelled with an organic solvent (such as ethylene dichl