Synthesis of novel cationic polymeric surfactants

A series of new cationic polymeric surfactants, comprising a short hydropho bic n-alkyl (C-12 or C-16) end-group and a long hydrophilic sequence of 17- 68 2-(dimethylamino)ethyl methacrylate (DMA) units, were successfully synth esized by oxyanion-initiated polymerization. A previously titrated solution of DMSO-K+ was used for quantitative formation of the potassium alcoholate initiators from the corresponding CI? or C16 alcohols. Optimum polymerizat ion conditions were found to be at or above room temperature, using THF as solvent. Under these conditions the polymers had relatively narrow polydisp ersities (M-w/M-n approximate to 1.25) and both GPC and NMR spectroscopy sh owed no residual monomer. NMR studies of the surfactants in CDCl3 also conf irmed that good control over the degree of polymerization was achieved, ind icating very high initiator efficiency. Cloud points of aqueous solutions o f selected polymeric surfactants were determined by turbidimetry and decrea sed with increasing DMA chain length, as expected. NMR spectra of the surfactants were also recorded in D2O. The C-12 surfacta nts each had roughly the same degree of polymerization of DMA in D2O as tha t obtained in CDCl3, suggesting molecular dissolution. In contrast, the app arent degrees of polymerization for the DMA blocks in the C16 surfactants w ere markedly higher in D2O than in CDCl3. This indicates reduced solvation for the C-16 moiety, which is consistent with micelle formation. Surface te nsiometry studies indicated higher surface activities for the C-12-based su rfactants compared to the C-16-based surfactants. Again, this is consistent with the hypothesis that the latter surfactants form intermolecular micell es in aqueous solution, whereas the C-12-based surfactants are molecularly dissolved. Dynamic light scattering and transmission electron microscopy st udies confirmed the existence of micelles in C-16 surfactant solutions but no micelles were observed for the CI? surfactants. Finally, a selectively d euterated C-12-based polymeric surfactant was also prepared for planned neu tron reflectivity studies at the air-water interface. (C) 2000 Elsevier Sci ence Ltd. All rights reserved.