Homopolymers of monomers represented by the general formula (3): wherein R1 represents a hydrogen atom or a methyl group; R2 and R3 each represent a substituted or unsubstituted alkyl group (preferably having 1 to 4 carbon atoms); or copolymers with polymerizable monomers such as styrene, acrylates or methacrylates as described above may also be used as positive charge control agents.