NMR SELF-DIFFUSION OF ASSOCIATIVE POLYMERS IN AQUEOUS-SOLUTION - THE INFLUENCE OF THE HYDROCARBON END-CHAIN LENGTH ON THE POLYMER TRANSPORTDYNAMICS IN SINGLE-COMPONENT AND 2-COMPONENT MIXTURES

This paper presents diffusion studies of two ''model'' associative pol ymers (hydrophobically end-capped poly(ethylene oxide))(AP) differing in end-group length, a factor of great significance in the transport r ate of APs in aqueous solution. An increase in end-group length was fo und to reduce the self-diffusion coefficient. As expected, it also gre atly influences the onset of aggregation, as monitored by static fluor escence, and the phase behavior. The longer the hydrocarbon end group, the lower the critical aggregation concentration and the lower the cl oud point of the polymer solution; i.e., the lower critical solution t emperature decreases. In line with oscillatory relaxation results obta ined by T. Annable et al. (J. Rheol. (N.Y.) 37, 695 (1993)), the data of the present paper show that AP transport in equimolar mixtures of t he two APs is characterized by two-component behavior over a wide rang e of semidilute polymer concentrations. The diffusion of the polymer i s therefore judged to be molecularly determined in this concentration region; i.e., the polymers diffuse independently within a network stru cture. The dynamic hydrophobic domains, keeping the network together, are considered to be mixed, containing end groups of both lengths. We also find that the cloud point temperature of these mixed solutions ar e situated between those of the single component solutions following a two-state relation. (C) 1997 Academic Press.