ASSOCIATIVE THICKENERS - NMR SELF-DIFFUSION AND RHEOLOGY STUDIES OF AQUEOUS-SOLUTIONS OF HYDROPHOBICALLY-MODIFIED POLY(OXYETHYLENE) POLYMERS

Nonionic associative polymers have been produced by hydrophobically modifying poly(oxyethylene) with hydrophobic end group straight hydrocarbon chain length varying from 8 to 18 carbon atoms. Solutions of these polymers in water have been studied by pulsed gradient spin-echo Fourier transform NMR self-diffusion (PGSE-FT NMR) and rheology measurements. The NMR results reveal a distribution of self-diffusion coefficients that broadens continuously with increasing concentration. The distribution is described by a stretched exponential from which mean diffusion coefficients are extracted. The concentration dependences of these diffusion coefficients are described by the stretched exponential of Phillies. The diffusion data have also been used to extract information on the coupling strength between the polymer clusters, described by a coupling parameter in the framework of the coupling model of Ngai, for molecular transport in polymer solutions. The coupling parameter increases both with concentration for each system and with hydrophobe end group chain length of the polymers. The rheology data on the same systems give partly complementary information on the aggregation state of the polymers in the semidilute concentration range. The combined information is used for a thorough discussion on the fundamental physics of systems of this kind.