Water-soluble complexes formed from hydrogen bonding interactions between a poly(ethylene glycol)-containing triblock copolymer and poly(methacrylic acid)

Poly(sodium styrenesulfonate)-block-poly(ethylene glycol)-block-poly(sodium styrenesulfonate) (PSS-PEG-PSS) was prepared via reversible addition-fragmentation chain transfer (RAFT) radical polymerization of sodium styrenesulfonate (SS) using a poly(ethylene glycol) (PEG)-based bifunctional macro-chain transfer agent in water. The reaction proceeded in the manner of living polymerization, suggesting that the number-average molecular weight increased linearly with monomer conversion, whereas the molecular weight distribution remained nearly constant below 1.30, independent of conversion. Poly(methacrylic acid) (PMA) homopolymer was also prepared via RAFT. When aqueous solutions of PSS-PEG-PSS and PMA were mixed below pH 5, water-soluble PSS-PEG-PSS/PMA complexes were formed as a result of hydrogen bonding interactions between the PEG block and the pendant carboxylic acids in PMA. The complex was characterized by H-1 NMR spin-spin relaxation time, light scattering and transmission electron microscopy measurement techniques. The hydrodynamic radius (R-h) of the complex depended on the mixing ratio of the PSS-PEG-PSS and PMA molecules. When the mole ratio of ethylene glycol units in PSS-PEG-PSS and the pendant carboxylic acids in PMA was nearly unity, the scattering intensity and R-h exhibited maximum values for PSS-PEG-PSS and PMA, which is indicative of stoichiometric complex formation. The complex dissociated at pH greater than 5 because the hydrogen bonding interaction ceased as a result of deprotonation of the pendant carboxylic acids in PMA.