Self-assembly of double hydrophobic block copolymers in water–ethanol mixtures: from micelles to thermoresponsive micellar gels

Abstract

Micellization and micellar gel formation of poly(styrene)-block-poly(methyl methacrylate) [PS-b-PMMA] are demonstrated in a water-ethanol solvent mixture; full hydration of the PMMA causes a large radius of gyration resulting in micellar gel formation at only 1 wt% polymer concentration.

Polymers with upper critical solution temperature behavior in alcohol/water solvent mixtures

“…This has been ascribed to the preferential waterhydrogen bonding to the ester moieties of the polymer as most of the water is present as single, non-clustered molecules in this ethanol concentration regime leading to favorable water-polymer hydrogen bonding (Scheme 1). [49,53,66,73] The formation of this hydration-shell around the carbonyl groups of the polymer is supported by small angle neutron scattering indicating the presence of a single deuterated water molecule per PMMA repeat unit. [53] The solubility of PMMA decreases with higher water content due to the formation of larger water clusters that need to be broken for hydration of the polymers.…”

“…[49,53,66,73] The formation of this hydration-shell around the carbonyl groups of the polymer is supported by small angle neutron scattering indicating the presence of a single deuterated water molecule per PMMA repeat unit. [53] The solubility of PMMA decreases with higher water content due to the formation of larger water clusters that need to be broken for hydration of the polymers. In contrast, with addition of more alcohol, the hydration of the polymer becomes less efficient as less water is present leading to a decrease of solubility.…”

“…In addition, the responsive behavior of such polymers could be well controlled by solvent composition, which allows tuning of the self-assembly of copolymers bearing such UCST polymer block(s). [53,54] Nonetheless, surprisingly few publications have appeared in recent years concerning UCST behavior of polymers in alcohol/water solvent mixtures, especially compared to the large amount of publications regarding LCST polymers. Two reasons may be ascribed to the low activity of this field: i) the importance of such ternary systems has been underestimated and overlooked; and ii) the alcohol-water-polymer ternary systems are very complicated and not well understood.…”

Temperature Induced Solubility Transitions of Various Poly(2-oxazoline)s in Ethanol-Water Solvent Mixtures

“…The monomer synthesis and subsequent polymerization of the poly(2-oxazoline)s with varying alkyl side chain are described elsewhere [45,46]. All investigated polymers (DP ~ 60) have a relatively narrow molar mass distribution with a polydispersity index around 1.20 as obtained by SEC investigations.…”

“…However, little is known about the solution behavior of polymers in water-ethanol mixtures, despite such mixtures being known to exhibit interesting abnormal mixing properties due to the presence of hydration shells around the ethanol molecules [40][41][42]. This peculiar mixing behavior has been demonstrated to result in solubility maxima for several drug molecules in aqueous ethanol [43,44] as well as for poly(methyl methacrylate) [45,46] and several poly(2-oxazoline)s as already mentioned previously [33][34][35].…”