Abstract: A process for the preparation of a compound or polymer having at least one functional group selected from hydroxyl, thiol, amino and carboxylic acid groups is characterized in that a compound or polymer (A) containing a group of formula (I), ##STR1## where Q represents O or S and X represents --O--, --S--, --NH-- or a direct bond, the group being linked to the remainder of the compound or polymer through a carbon atom, is reacted with a compound (B) containing at least two functional groups selected from hydroxyl, thiol, amino and carboxylic acid groups, one of which functional groups (II) reacts with the group of formula (I) and one of which functional groups (III) is substantially unreactive with the group of formula (I) under the conditions of reaction, so that the compound (B) becomes bonded to (A) through the reaction of groups (I) and (II) forming a compound or polymer containing unreacted functional groups (III).