A New Strictly Alternating Comblike Amphiphilic Polymer Based on PEG. 2. Associative Behavior of a High Molecular Weight Sample and Interaction with SDS

Abstract

We describe the associative behavior of a strictly alternating comblike amphiphilic polymer in aqueous surfactant (sodium dodecyl sulfate (SDS)) solutions. The polymer contains normal stearyl pendent hydrophobic groups separated by poly(ethylene glycol) (PEG) of molecular weight 8000. The average number of hydrophobes per chain is 9. In the dilute regime in the presence of very low amount of SDS, the polymer associates mainly in flowerlike micelles very similar to those formed by a sample of similar structure but a lower degree of polymerization (on average, two to three hydrophobes per chain). Further addition of SDS leads to the formation of mixed micelles of decreasing NR (number of hydrophobes from the polymer per micelle). Flowerlike conformation is preserved until a SDS concentration which coincides with the critical aggregation concentration (cac) of SDS in the presence of poly(ethylene oxide) (PEO), after which the structure is disrupted. In the absence of SDS, below the polymer overlapping concentration c*, bridging between micelles leads to phase separation between a highly viscous phase rich in polymer (network of interconnected flowerlike micelles) and a phase of very low viscosity. In the semidilute regime, the viscosity against SDS concentration exhibits a maximum, a classical result for hydrophobically modified polymers interacting with surfactant micelles. The covalent linkage between the PEG−C18 sequences belonging to the same polymer chain that bridges multiple micelles is responsible for the enhanced viscosity as compared to the telechelic PEO. Rheological data show evidence of the transition from a network of interconnected flowerlike micelles to an extended uniformly connected network upon addition of SDS.