Critical Solution Temperature Phase Separation Research Articles

Temperature-Responsive Deep Eutectic Solvents for Highly Selective Separation of 5-Hydroxymethylfurfural from Reaction Mixture

5-Hydroxymethylfurfural (HMF) is a key biobased platform compound for the production of high-value chemicals and fuels. However, separation and purification of HMF is currently the bottleneck for HMF production. In this work, a novel class of temperature-responsive deep eutectic solvent (DES)–water systems have been explored to selectively separate HMF from reaction mixtures. The fructose dehydration reaction was conducted in homogeneous DES–H2O systems, and then, the produced HMF was migrated to the DES-rich phase while the unreacted fructose was retained in the H2O-rich phase upon cooling. Thus, selective separation of HMF was realized. It was found that water–water and DES–DES interactions predominate over DES–water interactions during cooling, thus resulting in upper critical solution temperature phase separation. Under optimal conditions, the partition coefficient and separation factor of HMF could reach up to 78 and 609, respectively, which is about 5 and 13 times those reported in ionic liquid-based aqueous biphasic systems. Furthermore, HMF could be removed from the DES-rich phase, giving a high recovery efficiency of 69%, which is much higher than the best value reported in the literature. At the same time, DES was regenerated and reused in the next process, and no obvious decrease in partition coefficient of HMF was observed after six cycles.

Dual entropic and enthalpic processes in the lower critical solution temperature phase separation of poly(vinyl methyl ether) aqueous solutions

ABSTRACTIn the lower critical solution temperature phase separation of poly(vinyl methyl ether) aqueous solutions, the process corresponding to the weakening of the hydrogen bond interaction with increasing temperature is dominant and occurs over the entire concentration region of solutions and over a broad temperature range from 30 to 41°C, giving rise to the energetic enthalpic effect during phase separation, while the conformational change, that is, collapse of the swollen polymer coils, occurs only in the swelling polymer solution when the water concentration is above 38.3 wt %, giving rise to the entropic effect during phase separation. In addition, the entropic process corresponding to the collapse of the polymer coils occurs in a much narrow theta temperature range from 35.5 to 37°C. If the solution is held at a constant temperature for a sufficiently long time, 90% collapse of the polymer coils occurs in only the 0.5 °C temperature region between 35.5 and 36°C. Accordingly, in the enthalpic process, the most dramatic blueshift of the νC‐O bond peak occurs in the temperature range between 35 and 41°C, while this blueshift is only approximately 2 cm−1 in the temperature range from 30 to 35°C, prior to the collapse of the polymer coils due to the entropic effect. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2019, 57, 323–330

Lattice cluster theory of associating polymers. IV. Phase behavior of telechelic polymer solutions

The newly developed lattice cluster theory (in Paper I) for the thermodynamics of solutions of telechelic polymers is used to examine the phase behavior of these complex fluids when effective polymer-solvent interactions are unfavorable. The telechelics are modeled as linear, fully flexible, polymer chains with mono-functional stickers at the two chain ends, and these chains are assumed to self-assemble upon cooling. Phase separation is generated through the interplay of self-assembly and polymer/solvent interactions that leads to an upper critical solution temperature phase separation. The variations of the boundaries for phase stability and the critical temperature and composition are analyzed in detail as functions of the number M of united atom groups in a telechelic chain and the microscopic nearest neighbor interaction energy ε(s) driving the self-assembly. The coupling between self-assembly and unfavorable polymer/solvent interactions produces a wide variety of nontrivial patterns of phase behavior, including an enhancement of miscibility accompanying the increase of the molar mass of the telechelics under certain circumstances. Special attention is devoted to understanding this unusual trend in miscibility.

Unified model of association-induced lower critical solution temperature phase separation and its application to solutions of telechelic poly(ethylene oxide) and of telechelic poly(N-isopropylacrylamide) in water

The authors present a model describing the coexistence of hydrophobic association and phase separation with lower critical solution temperature (LCST) in aqueous solutions of polymers carrying short hydrophobic chains at both chain ends (telechelic associating polymers). The LCST of these solutions is found to decrease along the sol/gel transition curve as a result of both end-chain association (association-induced phase separation) and direct hydrophobic interaction of the end chains with water. The authors relate the magnitude of the LCST decrease to a hydration cooperativity parameter sigma. The LCST decreases substantially (approximately 100 K) in the case of random hydration (sigma=1), whereas only a small shift (approximately 5-10 K) occurs in the case of cooperative hydration (sigma=0.3). The molecular weight dependence of the LCST drop is studied in detail in each case. The results are compared with experimental observations of the cloud points of telechelic poly(ethylene oxide) solutions, in which random hydration predominates, and of telechelic poly(N-isopropylacrylamide) solutions, in which cooperative hydration prevails.

Synthesis and blends of pentabromobenzyl acrylate copolymers

The synthesis of styrene–pentabromobenzyl acrylate (S–PBBA) and methyl methacrylate–pentabromobenzyl acrylate (MMA–PBBA) copolymers and the phase behavior of their blends is reported. The miscibility of S–PBBA copolymers with polystyrene (PS), tetramethyl polycarbonate (TMPC), and poly(phenylene oxide) (PPO), and of MMA–PBBA copolymers with poly(methyl methacrylate) (PMMA) and polycarbonate (PC) was examined as a function of copolymer composition. Additionally, regions of miscibility were established for blends of both PBBA copolymer families with styrene–acrylonitrile (SAN) and styrene–maleic anhydride (SMA) copolymers, as well as for S–PBBA copolymers with styrene–methyl methacrylate (SMMA) copolymers. From the isothermal phase boundaries, repeat unit interaction energies with PBBA were estimated using previously established binary interaction energies, a binary interaction model, and the Flory–Huggins theory. In all cases, the interactions with PBBA were found to be highly endothermic. Lower critical solution temperature phase separation was measured for selected blends and compared with predictions based on the Sanchez–Lacombe equation-of-state.