Biocompatibles UK Limited

Yinghua Ma

Andrew Lennard Lewis

Steven Peter Armes

Sean Leo Willis

Emma Janice Lobb

Block copolymers comprise a core block formed of hydrophilic monomers and have pendant zwitterionic groups, and at least two terminal blocks, comprising stimulus-responsive groups. The core block has a degree of polymerisation of at least 100, whilst the terminal blocks have an average degree of polymerisation of at least 20. A solution of polymer in a liquid may be caused to change its characteristics, for instance rheology, upon being subjected to a stimulus such as a change in temperature or pH. Examples comprise core blocks formed of 2-methacryloyloxyethyl-2'-trimethylammonium ethylphosphate inner salt (MPC) and terminal blocks formed of 2-(diisopropylamino)ethyl methacrylate. Upon changing the pH from around 2 to around 8, an aqueous solution of the block copolymer gels, the solution becoming mobile again upon lowering the pH. The effect is due to deprotonation of a quaternary ammonium pendant ion to form a non-ionised group and subsequent protonation to form an ionised group. This changes the hydrophilicity of the terminal blocks and allowing formation of a network of micellar structures when the pendant groups are not ionised and relatively hydrophobic and associated in micelles.

Block copolymers

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.

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Surrey, United Kingdom

Yinghua Ma