Triblock copolymers of styrene and sodium methacrylate as smart materials: synthesis and rheological characterization

Abstract

Well-defined amphiphilic triblock poly(sodium methacrylate)-polystyrene-poly(sodium methacrylate) (PMAA-b-PS-b-PMAA) copolymers characterized by a different length of either the hydrophilic or the hydrophobic block have been synthesized by ATRP. In solution the micelle-like aggregates consist of a collapsed PS core surrounded by stretched charged PMAA chains. The micelles are kinetically 'frozen' and as a consequence the triblock copolymers do not show a significant surface activity. The hydrophilic block length has a major influence on the rheology, the shortest PMAA blocks yielding the strongest gels (at the same total weight concentration). The hydrophobic block length has only a minor influence until a certain threshold, below which the hydrophobic interactions are too weak resulting in weak gels. A mathematical model is used to describe the micelle radius and the results were in good agreement with the experimentally found radius in transmission electron microscopy. The influences of the ionic strength, pH and temperature on the rheology has also been investigated, showing the potential of these polymers as smart hydrogels. The change in conformation of the hydrophilic corona from the collapsed state to the stretched state by changing the pH was quantified with zeta-potential measurements. To the best of our knowledge, this is the first systematic investigation of this kind of triblock copolymers in terms of their rheological behavior in water.

The effect of macromolecular structure on the rheology and surface properties of amphiphilic random polystyrene-r-poly(meth)acrylate copolymers prepared by RDRP

“…8 Interestingly, this is another clear difference with analogous block copolymers, which are aggregated in ''frozen'' micelles and do not display any surface activity. 20 The PS-r-AA 1 : 4.23…”

“…The interesting thing about these frozen micelles is that, in this case, the polymer solution displays a surface tension value similar to water. 20,21 Although much less frequent, there are also examples of studies of random or gradient structures. For example, Lee et al synthesized random, gradient and block copolymers using 2-dimethylaminoethyl methacrylate and n-butyl methacrylate and studied their aggregation properties.…”

“…To the best of our knowledge, the solution rheology of various random copolymers of styrene and sodium (meth)acrylate (PS-r-AA PS-r-MAA) was never studied before, although similar studies were carried out by our group on diblock, triblock and star-block copolymers PS-b-PMAA. 2,7,20 Finally, water solutions were characterized by surface tension measurements, cryo-TEM microscopy and fluorescent probe UVvis spectra, to investigate more in detail the structure dependence of the aggregation behavior of such polymers.…”

Design of a pH-responsive Conductive Nanocomposite Based on MWCNTs Stabilized in Water by Amphiphilic Block Copolymers

“…The polymers used in this study are indeed known to form colloidal micellar aggregates in water, as we have discussed in previous research [35][36][37][38]. If the polymers would form micelles around the MWCNTs like surfactants do [44] (PS/nanotube forming the core and PAA the corona as is visualized in Figure 6), the PAA length would not make a difference as it merely determines the thickness of the protecting layer Preprints (www.preprints.org) | NOT PEER-REVIEWED | Posted: 12 August 2019 doi:10.20944/preprints201908.0142.v1…”

“…A copolymer of PAA and polystyrene should therefore result in more stable dispersions which is more static (Figure 1). PS-PAA block copolymers are known to form colloidal gels sensitive to external stimuli such as pH and salinity [35][36][37][38]. The dispersion stability compared to PAA could be significantly improved by micelle formation around the CNT, as it has been shown in water/DMF solution for cross-linked PS-b-PAA in a study by Kang and Taton [39].…”