Polymers and their synthesis

A substituted polysaccharide useful as a macroinitiator for preparing graft polysaccharide polymers by controlled graft polymerisation, in which at least one sugar unit of the polysaccharide is substituted by a group of the formula

• —W—(X)p-(L)q-(Y)r-Z
• in which
• W represents a group —O— or —NR1—, where R1 represents a hydrogen atom or an optionally substituted alkyl group, preferably a hydrogen atom;
• p, q and r are each Independently 0 or 1;
• L represents an optionally substituted alkylene, cycloalkylene, arylene or heteroarylene group;
• X and Y each independently represent a group —CH2—, —CO—, —O—CO—, —CO—O—, —NH—CO—, —CO—NH—, —CH(OH)—CH2—, —CH2—CH(OH)—, —CH2—O—CO—, —CO—O—CH2—, —CH2—CO—O—, —O—CO—CH2—, —O—CO—NH—, —NH—CO—O—, —(CR2R3)s—CO—, —CO—(CR2R3)s—, —(CR2R3)t—O—, —O—(CR2R3)t—, —(CR2R3)u—SO—, —SO—(CR2R3)u—, —(CR2R3)v—SO2—, —SO2—(CR2R3)v— or —NH—CO—NH, where s, t, u and v are each independently 0, 1, 2 or 3 and R2 and R3 each independently represent a hydrogen atom or an optionally substituted alkyl group;
• and
• Z comprises a halogen atom and represents a control agent site from which a polymer may propagate during a free radical polymerisation process,
• the substituted polysaccharide having the general formula
• wherein each SU represents a sugar unit in a polysaccharide backbone;
• a represents the number of unsubstituted sugar units as a percentage of the total number of sugar units and is in the range from 0 to 99.9%,
• b represents the number of substituted sugar units as a percentage of the total number of sugar units and is in the range from 0.1 to 100%, preferably 1 to 35%, more preferably 1 to 20%;
• m represents the degree of substitution per sugar unit and is from 1 to 3,
• in which the polysaccharide has a β-1,4-linked backbone.