Synthesis of water-soluble polymers via atom transfer radical polymerisation.
A study of the atom transfer radical polymerisation (ATRP) of water-soluble, acidic,
monomers was carried out in aqueous media. The ATRP of sodium methacrylate
(MAANa) produced polymers with controlled molecular weights and narrow
polydispersities (Me/M, - 1.3) at 90°C. This is the first reported example of direct
polymerisation of an acidic monomer via ATRP. Previously, such acidic polymers were
produced by polymerisation of protected monomers. In this thesis, copper(l) bromide and
iron(II) bromide were investigated as ATRP catalysts. Both were found to be effective
when solubilised by 2,2'-bipyridine (bipy). Monomer conversions between 75 and 85 %
were obtained in the presence of Cu(l)Brlbipy, and conversions as high as 94 % were
obtained in the presence of Fe(II)Br2Ibipy. Kinetic studies carried out on the ATRP of
MAANa using the CuBrlbipy catalyst and an oligo(ethylene glycol)-based initiator
indicated that polymerisation proceeded via first order kinetics with respect to monomer
consumption, and that molecular weight increased linearly with conversion. This is as
expected for a living polymerisation. At approximately 75 - 85 % conversion, however,
premature termination occurred. Both bromine microanalyses and 'n and 13CNMR
studies indicated that the halide-capped polymer chain-ends undergo HBr elimination.
Low molecular weight « 10,000 g mol") MAANa homopolymers and oligo(ethylene
glycol)-sodium methacrylate block copolymers (PEG-b-PMAANa) were examined as
possible macro initiators for the ATRP of sodium 4-styrenesulfonate (SSNa), potassium 3-
sulfopropyl methacrylate (SPMAK) and sodium allyl sulfonate (SAS). PEG-b-PMAANa
was found to initiate the ATRP of SSNa, yielding a polymer with controlled molecular
weight and a polydispersity of 1.23. Initiation of the ATRP of SPMAK and SAS was less
successful. This was likely due to the loss of functionality of the MAANa-based
polymers. Block copolymers were obtained, however, by macroinitiating the aqueous
ATRP of MAANa using a monomethoxy-capped oligo(ethylene glycol) methacrylate
Successful ATRP of MAANa was also achievable at ambient temperatures in the
presence of a co-solvent, 2-(dimethylamino)ethanol, DMAE. DMAE appears to
dramatically increase the rate of polymerisation whilst still maintaining control when used
in equimolar quantities (relative to the monomer). Polymers with predetermined
molecular weights and narrow polydispersities were produced in good yield (up to 86 %
conversion) within five minutes at 20°C.
The ATRP of other hydrophilic monomers was also investigated, albeit in less detail.
These monomers included sodium acrylate, mono-2-(methacryloyloxy)ethyl succinate, 2-
hydroxyethyl acrylate, itaconic acid, and 2-acrylamido-2-methyl-propanesulfonic acid.
Generally less control was achieved for such syntheses than for the ATRP of MAANa.