Rheological Properties of Aqueous Micellar Gels of a Thermo- and pH-Sensitive ABA Triblock Copolymer

Abstract

This article presents a systematic study of the effect of pH on the rheological properties of aqueous micellar gels formed from 10.0 wt % aqueous solutions of a thermo- and pH-sensitive ABA triblock copolymer, poly(ethoxydi(ethylene glycol) acrylate-co-acrylic acid)-b-poly(ethylene oxide)-b-poly(ethoxydi(ethylene glycol) acrylate-co-acrylic acid) (P(DEGEA-co-AA)-b-PEO-b-P(DEGEA-co-AA)). The block copolymer was synthesized by atom transfer radical polymerization of DEGEA and tert-butyl acrylate with a molar ratio of 100:5 from a difunctional PEO macroinitiator and subsequent removal of tert-butyl groups using trifluoroacetic acid. PDEGEA is a thermosensitive water-soluble polymer with a cloud point of 9 °C in water. The thermo-induced sol-gel transition temperature (T(sol-gel)) of the 10.0 wt % aqueous solution of P(DEGEA-co-AA)-b-PEO-b-P(DEGEA-co-AA) can be continuously and reversibly tuned over a wide temperature range by varying the solution pH. The sol-gel transition became broader with the increase of pH, which stemmed from the weaker and broader LCST transition of P(DEGEA-co-AA) blocks at higher pH values. The maximum value of dynamic storage modulus, obtained from heating ramp, and the plateau storage moduli (G(N)), evaluated from frequency sweeps at three normalized temperatures (T/T(sol-gel) = 1.025, 1.032, and 1.039), decreased with the increase of pH from 3.00 to 5.40 with the sharpest drop observed at pH = ∼4.7. The decrease in G(N) reflects the reduction of the number of bridging polymer chains and simultaneously the increase of the numbers of loops and dangling polymer chains. The ionization of carboxylic acid groups at higher pH values introduced charges onto the thermosensitive blocks and made the polymer chains more hydrophilic, facilitating the formation of loops and dangling chains in the gels. The increase in the number of dangling polymer chains with the increase of pH was supported by fluorescence spectroscopy studies, which showed that the critical micelle concentration of P(DEGEA-co-AA)-b-PEO-b-P(DEGEA-co-AA) at a temperature corresponding to T(sol-gel) was higher at a higher pH. The results reported in this article showed that both T(sol-gel) and gel strength can be tuned by varying the solution pH, providing greater design flexibility for potential applications.

Sol–gel transition of novel temperature responsive ABA triblock copolymer P(MEO2MA-co-HMAM)-b-PEG-b-P(MEO2MA-co- HMAM)

“…The PDIs of the triblock copolymers PMH7, PMH8 and PMH9 are 1.454, 1.230 and 1.276, respectively ( Table 1). The PDI indicates that the polymerization was well controlled [14,15].…”

“…These thermosensitive micellar gels had been investigated for applications in controlled release of substances and tissue engineering because of their unique thermoinduced in situ sol-gel transition and the nature of physical cross-linking. (2) If the A block is permanently water soluble and B block is thermosensitive exhibiting an LCST in water, the polymer molecules self-assemble into discrete, often spherical, micelles at temperatures above the LCST and the sol-gel transition is brought about by the packing of micelles into an ordered structure [15].…”

Study on the solution properties of ZnO QDs-embedded MEO2MA m –HEMA n –MEO2MA m triblock copolymers

“…Recently, Lutz et al [11][12][13] reported a new class of water-soluble copolymers based on 2-(2-methoxyethoxy) ethyl methacrylate (MEO 2 MA). It has been confirmed that these copolymers can be considered as potential candidates for application in biotechnology [14][15][16]. In spite of these advantages, intermolecular interactions are too weak to form crosslinking gel upon heating-induced phase transition for MEO 2 MA [17].…”

“…To further study the sol-gel transition and rheological properties of copolymer solutions, we recorded the dynamic moduli (G′ and G″) of copolymer solutions at various temperatures [16,32]. Figure 9 shows the data from an oscillatory shear measurement of the 10.0 wt% aqueous solutions.…”

Hydrogels for Cell Encapsulation and Bioprinting

“…The gelation kinetics of physical micellar gels depends on the strength and number density of physical crosslinks [105,107]. The gelation kinetics of covalently-bonded chemical gels depends on several factors including the concentration and distribution of crosslinkable groups and initiator [104,[108][109][110].…”