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 mo difying poly(oxyethylene) with hydrophobic end group straight hydrocar bon chain length varying from 8 to 18 carbon atoms. Solutions of these polymers in water have been studied by pulsed gradient spin-echo Four ier transform NMR self-diffusion (PGSE-FT NMR) and rheology measuremen ts. The NMR results reveal a distribution of self-diffusion coefficien ts that broadens continuously with increasing concentration. The distr ibution is described by a stretched exponential from which mean diffus ion 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 informatio n on the coupling strength between the polymer clusters, described by a coupling parameter in the framework of the coupling model of Ngai, f or molecular transport in polymer solutions. The coupling parameter in creases both with concentration for each system and with hydrophobe en d group chain length of the polymers. The rheology data on the same sy stems give partly complementary information on the aggregation state o f the polymers in the semidilute concentration range. The combined inf ormation is used for a thorough discussion on the fundamental physics of systems of this kind.