Viscoelastic properties in water of comb associative polymers based on poly(ethylene oxide)

We describe aspects of the rheological behavior in aqueous solution of three associative polymers with a comb architecture. These polymers of identical structure but different molecular weight are based on poly(ethylene glycol) of M = 8400, joined by a coupling agent bearing a C(14)H(29)-group. In steady shear, these polymer solutions exhibit a strong increase in low shear viscosity for concentrations between 1 and 2 wt %, and a sharp shear thinning transition at a hear rate of ca. 100 Hz. Some differences are seen between the "as prepared" and recrystallized samples. Oscillatory shear and first normal stress difference (N(1)) measurements were carried out on the lowest molecular weight sample, with an average of three pendant C(14)H(29)-groups per chain, and compared to the behavior of a telechelic polymer of similar molecular weight with C(16)H(33)-end groups. N(1) measurements on both systems show similar behavior: a sharp increase in N(1) which persists well into the shear thinning domain, followed by a decrease in N(1) as the shear rate is increased further. The decrease in N(1) and the strong shear thinning together suggest that the networks break down at high shear rates. In oscillatory shear experiments, major differences between the two types of polymers are apparent. The comb polymer exhibits a broad distribution of relaxation times, with a longest relaxation time of ca. 7 s, 2 orders of magnitude longer than that found for the telechelic polymer. From independent information about micellar structures present in the system, we calculate the functionality of the networks formed. For a given concentration, we find a much higher fraction of bridging chains and a much lower fraction of looped chains for the comb polymer than for the corresponding telechelic polymer.