Solution Temperature Behavior Of Poly Research Articles

Amplification of hofmeister effect by alcohols.

We have demonstrated that Hofmeister effect can be amplified by adding alcohols to aqueous solutions. The lower critical solution temperature behavior of poly(N-isopropylacrylamide) has been employed as the model system to study the amplification of Hofmeister effect. The alcohols can more effectively amplify the Hofmeister effect following the series methanol < ethanol < 1-propanol < 2-propanol for the monohydric alcohols and following the series d-sorbitol ≈ xylitol ≈ meso-erythritol < glycerol < ethylene glycol < methanol for the polyhydric alcohols. Our study reveals that the relative extent of amplification of Hofmeister effect is determined by the stability of the water/alcohol complex, which is strongly dependent on the chemical structure of alcohols. The more stable solvent complex formed via stronger hydrogen bonds can more effectively differentiate the anions through the anion-solvent complex interactions, resulting in a stronger amplification of Hofmeister effect. This study provides an alternative method to tune the relative strength of Hofmeister effect besides salt concentration.

Dual stimuli-responsive polymers derived from α-amino acids: Effects of molecular structure, molecular weight and end-group

Four kinds of well defined poly(N-methacryloyl-L-amino acid)s were prepared via reversible addition fragmentation chain transfer polymerization. The effects of molecular structure, molecular weight, and end-group on their responsive properties in water were investigated. We found that the monomer structure is critical for the polymer to exhibit stimuli-responsive properties in water; only polymers derived from aspartic acid showed defined dual thermo- and pH-responsive properties. To study the effects of molecular weight and end group on the lower critical solution temperature behavior of poly(N-methacryloyl-L-β-isopropyl aspartic acid) (PMAIPAC), a series of PMAIPAC homopolymers with controlled molecular weights and narrow polydispersities were prepared and treated with excess radical initiators to give defined end groups. The cloud point of PMAIPAC was found to increase with the increase of solution pH, due to the ionization of carboxylic acid groups, and decrease with the increase of molecular weight. The structure of end groups also affects the cloud point of PMAIPAC particularly for low molecular weight samples at low pH.

Tuning the upper critical solution temperature behavior of poly(methyl methacrylate) in aqueous ethanol by modification of an activated ester comonomer

A statistical copolymer of methyl methacrylate (MMA) and pentafluorophenyl methacrylate (PFPMA, 6 mol%) exhibits upper critical solution temperature (UCST) behavior in aqueous ethanol solutions tunable by post-polymerization modification with different amines. The phase transition behavior of the obtained copolymers in aqueous ethanol was evaluated in detail. As expected, all copolymers reveal an upper critical solution temperature with 55 vol% or higher ethanol content. Furthermore, the solubility in aqueous ethanol of the copolymer can be increased by the introduction of hydrophilic moieties. When hydrophobic substituents are introduced a decrease in solubility was observed with low content of ethanol and an increase in solubility when adding more ethanol. As such, the thermoresponsive behavior of PMMA can be significantly altered by post-modification of 6 mol% of the reactive comonomer units. The hysteresis of the polymer phase transitions between heating and cooling was found to be strongly dependent on the polarity of the amine substituent and the ethanol/water ratio. The metastability of the hysteresis is addressed based on isothermal turbidity studies.

Lower critical solution temperature behavior of poly(2-chloroethyl vinyl ether-alt-maleic anhydride) in organic media

Lower critical solution temperature behavior of poly(2-chloroethyl vinyl ether- alt -maleic anhydride) in organic media

Upper Critical Solution Temperature Behavior of Poly(N-isopropylacrylamide) in an Ionic Liquid and Preparation of Thermo-sensitive Nonvolatile Gels

Abstract Poly(N-isopropylacrylamide) and its gels exhibited upper critical solution temperature behavior in a hydrophobic ionic liquid, 1-ethyl-3-methylimidazolium bis(trifluoromethane sulfone)imide, which may be utilized to prepare stimuli-sensitive polymer systems without the problem of solvent evaporation.

Roles of Enthalpy, Entropy, and Hydrogen Bonding in the Lower Critical Solution Temperature Behavior of Poly(ethylene oxide)/Water Solutions

Analysis of the temperature and composition dependence of the excess thermodynamic properties for oligomers of poly(ethylene oxide) (PEO) in aqueous solution obtained from molecular dynamics simulations reveals that the lower critical solution temperature (LCST) behavior of PEO/water solutions is enthalpy-driven. At lower temperatures, the formation of ether−water hydrogen bonds results in a very favorable ΔG EX consistent with the consolubility of PEO and water. Increasing temperature leads to a dramatic reduction in favorable ether−water interactions due to break-up of ether−water hydrogen bonding, while relatively persistent water−water hydrogen bonding maintains the energetic penalty associated with disrupted water−water interactions upon insertion of the ether. The entropy gain associated with the break-up of ether−water hydrogen bonds and reduction in the structure of hydrating water with increasing temperature is insufficient to offset the unfavorable enthalpic effects associated with the break-up of the ether−water hydrogen bonds.