The present invention discloses a method of making core-shell polymer particles, comprising forming a linking-group-containing polymer by derivatizing a hydroxy-group-containing polymer, comprising hydroxy groups on adjacent carbon atoms with a linking agent, that is a compound comprising both an aldehyde moiety and an amine moiety, wherein one or more acetal moieties are formed in the linking-group-containing polymer, each acetal formed by the reaction of the aldehyde moiety in the linking agent with two hydroxy groups in the linking-group-containing polymer, wherein the amine moiety then becomes a linking group pendent from the linking-group-containing polymer, wherein the linking group is capable of reacting with a precursor group in the precursor polymer. Also disclosed are compositions comprising insoluble core-shell particles made by the method.