Polymers may be made from zwitterionic monomers having controlled
architectures and molecular weights, using living polymerisations such as
group or atom transfer radical polymerisation. For instance polymers may
be formed by atom transfer radical polymerisation using a copper chloride
catalyst, a ligand which is water soluble, and a water soluble tertiary
alkyl halide initiator to form homopolymers having controlled
polydispersities of less than 1.5 and block copolymers with other
hydrophilic or hydrophobic monomers. One suitable zwitterionic monomer is
2-methacryloyloxy-2'-trimethylammoniumethyl phosphate inner salt. The
block copolymers may spontaneously form micelles, believed to have
zwitterionic, for instance phosphorylcholine, groups at the external
surface, which may be useful as drug delivery systems with improved
biocompatibility.