A modified particle is disclosed wherein a particle has an attached group having the formula: wherein Ar represents an aromatic group; R1 represents a bond, an arylene group, an alkylene group, wherein R4 is an alkyl or alkylene group or an aryl or arylene group; R2 and R3, which can be the same or different, represent hydrogen, an alkyl group, an aryl group, —OR5, —NHR5, —NR5R5, or —SR5, wherein R5, which is the same or different, represents an alkyl group or an aryl group; and SFR represents a stable free radical. Also disclosed is a modified particle or aggregate having attached a group having the formula: wherein CoupA represents a Si-containing group, a Ti-containing group, or a Zr-containing group; R8 and R9, which can be the same or different, represent hydrogen, an alkyl group, an aryl group, —OR10, —NHR10, —NR10R10, or —SR10, wherein R10 represents an alkyl group or an aryl group; SFR represents a stable free radical; and n is an integer of from 1 to 3. A modified particle having an attached —SFR or —X—SFR is additionally disclosed. Also, modified particles with attached polymers are also disclosed as well as methods of making the modified particles.