Rheological Behavior of Aqueous Micellar Solutions of a Triblock Copolymer of Ethylene Oxide and 1,2-Butylene Oxide:  B₁₀E₄₁₀B₁₀

Abstract

A triblock copolymer of ethylene oxide and 1,2-butylene oxide, denoted B10E410B10, was prepared by sequential oxyanionic polymerization and characterized by 13C NMR spectroscopy and gel permeation chromatography. Micellization and the formation of micelle clusters in dilute aqueous solution, the latter a consequence of micelle bridging, was confirmed by dynamic light scattering, and average association numbers of the micelles were determined by static light scattering for T = 20-40 degrees C. The frequency dependence of the dynamic storage and loss moduli was investigated for solutions in the range of 5-20 wt %. Comparison with results for poly(oxyethylene) dialkyl ethers (10 wt %, T = 25 degrees C) indicated that the viscoelasticity of a copolymer with terminal B10 hydrophobic blocks was roughly equivalent to one with terminal C14 alkyl chains. The temperature dependence of the modulus was investigated for 15 wt % solutions at T = 5-40 degrees C. Superposition of the data led, via an Arrhenius plot, to an activation energy for the relaxation process of -40 kJ mol(-1). The negative value contrasts with the positive values found for poly(oxyethylene) dialkyl ethers and related HEUR copolymers with urethane-linked terminal alkyl chains. This difference is attributed to the block-length distribution in copolymer B10E410B10, whereby the activation energy of the relaxation process has a positive contribution from the disengagement of B blocks from micelles but a negative contribution from micellization. The negative value of the activation energy for solutions of B10E410B10 was confirmed by determining the temperature dependence of the zero-shear viscosity of its 15 wt % solution.

Concentration dependence of rheological properties of telechelic associative polymer solutions

“…Mistry et al reported non-single Maxwell relaxation modulus data for relatively high concentration poly(butylene oxide)-(etylene oxide)-(butylene oxide) triblock copolymer solutions [30]. Some shear relaxation modulus data for relatively high concentration HEUR solutions [2,4] also deviate from the single Maxwellian form.…”

Aqueous Gels of Triblock Copolymers of Ethylene Oxide and 1,2‐Butylene Oxide (Type BEB) Studied by Rheometry

“…It is known [17] that the dynamic moduli of solutions of copolymer B 12 E 114 B 12 can be scaled against frequency approximately in the manner defined by Trappe and Weitz for colloid particles, while frequency scans obtained for solutions of copolymer B 10 E 410 B 10 are better modelled by a combination of Maxwell elements with a distribution of relaxation times. [22] The present copolymers with E 227 central blocks represent an intermediate case.…”

“…Moreover, the stability of the micelles of E/B copolymers, and so the extent of micellisation, is much affected by the distribution of Bblock lengths, as discussed previously for BEB copolymers. [22] Micelles (and so gels) of copolymers with alkyl blocks, e.g. HEUR copolymers and poly(oxyethylene) diand mono-alkyl ethers, [16,31] are stable down to low temperatures, a consequence of the high hydrophobicity and the uniformity of their alkyl chains.…”

“…[22] Regarding the rheological behaviour of micellar solutions, that of the short copolymers should tend towards that exhibited by weakly attractive colloids, while the long ones should tend towards that of network polymers. It is known [17] that the dynamic moduli of solutions of copolymer B 12 E 114 B 12 can be scaled against frequency approximately in the manner defined by Trappe and Weitz for colloid particles, while frequency scans obtained for solutions of copolymer B 10 E 410 B 10 are better modelled by a combination of Maxwell elements with a distribution of relaxation times.…”

Rheology of associative polymer solutions

“…The reason is that for this system the fraction of chains that form micelles increased with increasing temperature so that increasing the temperature is equivalent to increasing the concentration. Mistry et al [36] determined the temperature dependence of the terminal relaxation of transient networks formed by the same triblock copolymer. Surprisingly, they found that the relaxation time increased with increasing temperature, contrary to what was observed for PEO chains end-capped with alkyl chains.…”