. . . "A modified particle is disclosed wherein a particle has an attached group having the formula: ##STR1## wherein Ar represents an aromatic group; R1 represents a bond, an arylene group, an alkylene group ##STR2## 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, --NR5" . . .