Viscoelastic Behavior of Semidilute Solutions of Multisticker Polymer Chains

Abstract

Multisticker polymer chains consisting of water-soluble polyacrylamides hydrophobically modified with low amounts of N,N-dihexylacrylamide have been prepared by a free radical micellar polymerization technique. This process gives multiblock copolymers in which the number and length of the hydrophobic blocks can be tuned by varying the surfactant over hydrophobe molar ratio. The viscoelastic behavior of semidilute solutions of various series of copolymers with variable molecular weights (M w ≈ 4.2 × 104−2.7 × 106), hydrophobe contents ([H] = 0.5−2 mol %), and hydrophobic block lengths (N H = 1−7 units per block) has been investigated as a function of polymer concentration, C, using steady-flow and oscillatory experiments. In the semidilute range, two different regimes can be clearly distinguished in the zero-shear viscosity η 0 = f(C) curves: a first unentangled regime where the viscosity increase rate strongly depends on N H and [H]; a second entangled regime where the viscosity follows a scaling behavior of the polymer concentration with an exponent close to 4, whatever [H] or N H. The linear viscoelasticity can be described by (i) a slow relaxation process with a plateau modulus that only depends on polymer concentration and (ii) other faster complex relaxation processes. In the latter regime, the results can be quite well accounted for by a hindered reptation model.

A new approach to the synthesis of hydrophobically associating polyacrylamide via the inverse miniemulsion polymerization in the presence of template

“…The viscosity of PDA-4 solution was higher than that of PDA-1 solution at the concentration above C * (0.30 g/dl), opposite tend was showed at the concentration below C * . This result indicated that PDA prepared with template exhibited a longer hydrophobic block characteristic, which made it more easily to form intermolecular association at the concentration above C * and intramolecular association at the concentration below C * [8,33,34]. It was interesting to note that the viscosity of PDA was higher than that of PAM without hydrophobically modified at the concentration below C * .…”

Micellar Synthesis and Properties of Hydrophobically Associating Polyampholytes

“…In all cases, the incorporation level of DiHexAM was nearly complete ( Table 1) as was already found for hydrophobically modified poly(acrylamides). [7,11,12,15,22,23,30] Several attempts to determine the hydrophobe incorporation level in the samples from series 3 were unsuccessful. The use of D 2 O, and its mixture with deuterated methanol or deuterated DMSO did not allow us to detect the signal of hydrophobic units protons in the spectrum.…”

Self-Healing Hydrogels Formed via Hydrophobic Interactions

“…where N Agg is the aggregation number of the surfactant, CMC is its critical micelle concentration, f HM is the mole fraction of HM in the comonomer feed, and N is the chain length of polymer [53]. Because incorporation of a small amount of hydrophobic groups in a hydrophilic polymer backbone results in polymers with extraordinary rheological properties in aqueous solutions, many studies have been carried out during the past two decades on the synthesis and solution properties of hydrophobically modified hydrophilic polymers [54,55].…”