A new strictly alternating comblike amphiphilic polymer based on PEG. 2. Associative behavior of a high molecular weight sample and interaction with SDS

We describe the associative behavior of a strictly alternating comblike amp hiphilic polymer in aqueous surfactant (sodium dodecyl sulfate (SDS)) solut ions. The polymer contains normal stearyl pendent hydrophobic groups separa ted by poly(ethylene glycol) (PEG) of molecular weight; 8000. The average n umber of hydrophobes per chain is 9. In the dilute regime in the presence o f very low amount of SDS, the polymer associates mainly in flowerlike micel les very similar to those formed by a sample of similar structure but a low er degree of polymerization (on average, two to three hydrophobes per chain ). Further addition of SDS leads to the formation of mixed micelles of decr easing NR (number of hydrophobes from the polymer per micelle). Flowerlike conformation is preserved until a SDS concentration which coincides with th e critical aggregation concentration (cac) of SDS in the presence of poly(e thylene oxide) (PEO), after which the structure is disrupted. In the absenc e of SDS, below the polymer overlapping concentration c*, bridging between micelles leads to phase separation between a highly viscous phase rich in p olymer (network of interconnected flowerlike micelles) and a phase of very low viscosity. In the semidilute regime, the viscosity against SDS concentr ation exhibits a maximum, a classical result for hydrophobically modified p olymers interacting with surfactant micelles. The covalent linkage between the PEG-C18 sequences belonging to the same polymer chain that bridges mult iple micelles is responsible for the enhanced viscosity as compared to the telechelic PEG. Rheological data show evidence of the transition from a net work of interconnected flowerlike micelles to an extended uniformly connect ed network upon addition of SDS.