Hydrophobically modified poly(N,N-dimethylacrylamide): Synthesis, aqueous solution behaviour, and rheological properties in aqueous mixtures with hydrophobically modified poly(sodium acrylate)

Copolymers of N,N-diemthylacrylamide with a low fraction of N-dodecylmethac rylamide or N-octadecylacrylamide were prepared by radical copolymerisation in methanol. The similar conversion rates of the comonomers during the pol ymerization reaction suggest that the microstructure of these copolymers is close to that of the random one. The great tendency of the alkyl groups to associate in an intra or intermolecular way, is clearly revealed from thei r rheological behaviour in aqueous solution and it is further supported by C-13 NMR and steady state fluorescence data. At low polymer concentration ( <0.01 g.cm(-3)) intramolecular association prevails and the viscosity of th e aqueous solution is clearly lower compared to that of the non-hydrophobic poly(N,N-diemthylacrylamide). compared to the hydrophobic derivatives of p oly(sodium acrylate), the present copolymers exhibit a higher tendency to a ggregate which is obviously due to the nonionic character of their backbone . The most interesting behaviour is observed by mixing solutions with a low viscosity of the hydrophobic derivatives of both poly(N,N-dimethylacrylami de) and poly(sodium acrylate). In some cases the viscosity of these mixture s is increased by several orders of magnitude. This behaviour is attributed to the formation of mixed aggregates involving alkyl groups from both kind s of copolymers.