Upper and lower critical solution temperatures in polyethylene solutions

Upper and lower critical solution temperatures have been determined for solutions of polyethylene in n-butyl acetate and n-amyl acetate over the molecular weight range of M_η = 1·36 × 10⁴ to 17·5 × 10⁴. Polyethylene solution in n-butyl acetate displays a smaller miscibility region than that of the polyethylene/n-amyl acetate system, as indicated by the relative positions of their upper and lower critical solution temperatures. Contributions of the energy and the equation of state terms to the χ1 parameter have been examined by an application of the Patterson-Delmas corresponding state theory to the experimental results of the polyethylene solutions.     

Upper and lower critical solution temperatures for star branched polystyrene in cyclohexane

Summary Upper and lower critical solution temperatures have been measured for star polystyrene samples, with varying degrees of branching, dissolved in cyclohexane. The effect of branching on the phase separation of these solutions is small in the lower critical region but becomes significant in the upper critical region. In all cases branching tends to extend the solubility range for polystyrene in cyclohexane. This is accentuated when the degree of branching is high and also when the molecular weight is low.Royal Society European Fellow 1975.British Council Fellow.     

Comonomer effect: Switching the lower critical solution temperature to upper critical solution temperature in thermo-pH sensitive binary graft copolymers

Hydrophilic biocompatible surfaces can be obtained by grafting stimuli-sensitive polymers onto commercially available medical devices. Thermo and pH-responsive polymers are two of the most studied materials due to their potential application as drug delivery systems. Poly(N-vinylcaprolactam) has a lower critical solution temperature (LCST) near to physiological temperature. However, when it is grafted with pH-sensitive moieties its LCST it is affected undergoing remarkable displacements. We studied the effect of acrylic acid (AAc), 4-vinylpyridine (4VP), and 1-vinylimidazole (Vim) on the LCST of N-vinylcaprolactam (NVCL) grafted onto silicone rubber (SR), and SR-g-NVCL (32.5 °C). The binary graft copolymers were obtained by ionizing grafting radiation using the simultaneous technique; the samples were characterized by Fourier transform infrared attenuated total reflectance (FTIR-ATR), cross-polarization magic angle spinning nuclear magnetic resonance (CP/MAS ¹³C-NMR), and thermogravimetrical analysis (TGA). LCST value was dramatically affected by the comonomer content; even it was observed the switching from LCST to upper critical solution temperature (UCST) for (SR-g-NVCL)-g-AAc and (SR-g-NVCL)-g-4VP samples. The observed behavior is rarely reported for binary graft copolymers. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 48170.     

Lower critical solution temperature (LCST) polymer solution for clear/cloud glazing applications

An aqueous-based clear/cloud solution was developed using poly(vinyl methyl ether) and an antifreeze mixture of ethylene and propylene glycols. The solution has a controllable cloud point from 15 to 90°C, freeze protection to ?46°C, and a density that prevents the precipitated polymer from settling and is fairly stable to UV degradation. A significantly smaller heat gain is achieved through the clear/cloud glazing when compared to a normal double-pane window. © 1994 John Wiley & Sons, Inc.     

Upper and lower critical solution temperatures for polystyrene in methyl cyclopentane and in dimethyl cyclohexane

The demixing of polystyrene in methyl cyclopentane, and in dimethyl cyclohexane has been investigated, and the upper and lower critical solution temperatures established for several polymer molecular weights. In the former solvent both upper and lower θ temperatures can be defined, but not in the latter where cloud point curves for the upper and lower critical temperatures coalesce for high molecular weights. The Patterson theory of polymer solutions has been applied to the data, and the characteristic free volume and exchange energy parameters have been evaluated. The lower critical solution temperatures are nearly the same in cyclopentane and methyl cyclopentane due to a compensation between the free volume and contact interaction terms. Solvent size effects are considered in order to explain the differences in the interaction of solvent with polymer.     

Upper and lower critical solution temperatures in poly (ethylene glycol) solutions

Upper and lower critical solution temperatures have been determined for solutions of poly(ethylene glycol) in t-butyl acetate and water over the molecular weight range of M_η = 2.18 × 10³ to ～1020 × 10³. The phase diagram for solutions of poly(ethylene glycol) (M_η = 719 × 10³) in t-butyl acetate was expressed as the ‘hour glass’ type, while the phase diagram for solution of poly(ethylene glycol) (M_η = 2.18 × 10³ to ～2.29 × 10³) in water was expressed as the ‘closed loop’ type. The value of the pressure dependence of the lower critical solution temperature $\text{(}\text{d}\text{T}\text{d}\text{P}\text{)}{}_{\mathrm{c}}$ in the poly(ethylene glycol) (M_η = 1020 × 10³)/water system over the pressure range of 0 to ～50 atm was negligibly small and positive.     

Upper critical solution temperature behaviour in poly(ether ether sulphone)/poly(ether ether ketone-co- ether ether sulphone) blends

Upper critical solution temperature (u.c.s.t.) phase behaviour was found in blends of the homopolymer poly(oxy-1,4-phenyleneoxy-1,4-phenylenesulphonyl-1,4-phenylene) (PEES) with the copolymer poly(oxy-l,4-phenyleneoxy-l,4-phenylenecarbonyl-l,4-phenylene-co-oxy-l,4-phenyleneoxy-1,4-phenylenesul-phonyl-1,4-phenylene) (COPEEKS) for copolymer compositions ranging from 43 mol% to 56 mol% of ether ether ketone (EEK) repeat units. Blend compositions studied ranged from 25wt% to 75wt% of PEES. The consolute temperature was found to occur at a PEES/COPEEKS blend composition of about 50/50 wt% and to increase with the EEK repeat unit content of the copolymer. This miscibility behaviour was interpreted, using a mean-field theoretical approach, in terms of a single positive segmental interaction parameter which ranged from 0.054 to 0.032.     

Hydrophobically modified polyglycidol – the control of lower critical solution temperature

Summary Polymers of glycidol (2,3-epoxypropanol-1) of different molar masses (between 2˙10⁴ and 2˙10⁵) and chain topology (linear and comb-like) were synthesised and used to obtain a series of temperature responsive water-soluble poly(glycidol-co-glycidol acetate)s. The degree of the substitution of the hydroxyl groups with the acetate groups influences the solution behaviour of the obtained copolymers, the cloud point may be controlled between +4°C and +lOO°C. Received: 24 September 2002/Revised version: 2 November 2002/ Accepted: 2 November 2002 Correspondence to Andrzej Dworak     

Lower critical solution temperature behavior of ethylene propylene copolymers in multicomponent solvents

The lower critical solution temperature (LCST) locus for ethylene-propylene copolymers has been determined as a function of pressure in a variety of single and multicomponent solvents. The lower critical end-point temperature (LCEP), which is the intersection of the LCST locus with the vapor-pressure curve, was found to be predictable from the solvent density as previously established for single-component solvents by Charlet and Delmas.¹ Dissolving a low-molecular hydrocarbon gas such as propylene in an alkane has a dramatic effect on lowering the LCEP, and can reduce phase-separation temperatures to levels at which this technique becomes attractive as a practical method for polymer recovery from diluents such as those used in solution polymerizations. Temperatures considerably above the LCEP are needed to minimize the residual polymer concentration in the solvent in the two-liquid-phase region. The solvent critical temperature must be approached for essentially complete elimination of the polymer from the solvent phase. The LCST locus was found to be a linear function of pressure for all of the systems investigated, and the slope of the line, d(LCST)/dP, could be well correlated as a function of solvent density and critical temperature. From the relationship between the LCEP and solvent density and the correlation for d(LCST)/dP, the location of the LCST locus can be readily predicted from a knowledge of solvent properties.     

pH值对硝酸铵水溶液临界爆炸温度的影响

研究了氯离子含量一定时pH值对硝酸铵水溶液临界爆温的影响。结果表明,氯离子质量分数为1．0×10^-4时,pH值越小,硝酸铵水溶液的临界爆温越低,且pH值与临界爆温值呈线性关系。本研究结果对硝酸铵的安全生产有重要的参考价值。     

Lower critical solution temperature behavior of amphiphilic copolymers based on polyaspartamide derivatives

Novel copolymers consisting of poly(N‐isopropylaminoethyl‐co‐6‐hydroxyhexyl aspartamide) and poly (N‐isopropylaminoethyl‐co‐hexyl aspartamide) were prepared from polysuccinimide, which was the thermal polycondensation product of L ‐aspartic acid, via a ring‐opening reaction with 6‐amino‐L ‐hexanol (AH) or hexylamine (HA) and N‐isopropylethylenediamine at different ratios. The copolymers, containing 75–90 mol % of AH and 35–45 mol % of HA, produced thermoresponsive polymers through their lower critical solution temperatures (LCSTs) in aqueous solution. We could control the LCST could be controlled by modifying the hydrophobic–hydrophilic balance by changing the content of AH or HA. The pH dependencies of the LCST were opposite in these two different copolymer systems. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Polymer-cosolvent systems: 5. Upper and lower critical solution temperatures of polystyrene in n-alkanes

The demixing behaviour of low molecular weight polystyrene in three n-alkanes (hexane, heptane and octane) has been established. Critical solution behaviour is a function of alkane chain length, and application of free volume theory shows this to be an entropic effect. The quality of n-alkanes, up to twenty carbons in length, as solvents for polystyrene has been estimated.     

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

Thermoresponsive polymers are of great importance in numerous nanotechnological and biomedical applications. Compared to polymers that undergo a lower critical solution temperature (LCST) phase transition in aqueous solution, i.e., demixing occurs upon heating, polymers exhibiting the reversed upper critical solution temperature (UCST) behavior in aqueous solution have been much less documented as it is more challenging to achieve this behavior in aqueous solutions. Furthermore, the high sensitivity of UCST behavior to minor variation in polymer structure and solution composition hampered the development of applications based on these polymers [18]. However, polymers with UCST transition in alcohol/water solvent mixtures are more commonly reported and exhibit promising properties for the preparation of ‘smart’ materials. This review will focus on the theory and development of such polymers with UCST behavior in alcohol/water solvent mixtures. By highlighting reported examples of UCST polymers in alcohol/water solvent mixtures, we aim to demonstrate the versatility and potential that such UCST polymers possess as biomedical and ‘smart’ materials.     

温度对HNS晶体和HNS溶液临界爆温的影响

为对比温度对六硝基芪(HNS)在晶体和溶液状态下不同的影响,采用自行设计的绝热加热装置测试了HNS晶体和HNS溶液的临界爆炸温度。为深入研究溶剂二甲基甲酰胺(DMF)与HNS相互作用的本质,通过构建HNS/DMF共混体系,用分子动力学(MD)方法对不同温度下的HNS/DMF和HNS晶体模型进行模拟计算。实验结果表明,相同质量的HNS晶体临界爆温比HNS/DMF溶液的临界爆炸温度低。模拟结果表明,HNS在晶体和溶液状态下,最大引发键(C—N)键长均随温度的增加而增大,且在相同温度下HNS晶体中的最大引发键比溶液状态下长;相同温度下晶体状态下的内聚能比溶液状态下的内聚能高;HNS/DMF的结合能随温度的升高先下降而后升高。     

Liquid-liquid phase splitting—III: Azeotropy and critical solution temperature in ternary systems

The simultaneous phenomena of critical solution and azeotropy in ternary systems is analysed. Conditions are determined for the formation of positive, negative, and positive-negative azeotropes. The corresponding phenomena are analyzed for a liquid phase described by G^E = Ax₁x₂ + Bx₁x₃ + Cx₂x₃ + x₁x₂x₃ + (D+Ex₁ + Fx₂).     

A brillouin scattering study of a polymer blend showing upper critical solution temperature behaviour

Summary The Brillouin spectra of a polymer blend of poly(styrene-co-allyl alcohol) and poly(neopentyl glycol adipate), showing upper critical solution temperature behaviour, have been measured as a function of temperature. Conspicuous changes have been observed in the Brillouin width near the cloud point and have been interpreted as arising from composition changes in the two originally distinct low-temperature microscopically separated liquid phases towards a common high-temperature solution.     

Introduction of pH-sensitive upper critical solution temperature (UCST) properties into branched polyethylenimine

We introduced upper critical solution temperature (UCST) properties into an amine-rich polymer, branched polyethylenimine (b-PEI) by a simple sulfopropylation reaction. The phase transition behavior of the N-sulfopropylated b-PEI (PS-PEI) derivatives was influenced by the degree of sulfopropylation, concentration, molecular weight, ionic strength, and pH. In particular, the phase transition temperature of PS-PEI was strongly dependent upon pH. As the pH decreased, the protonable amine residues of PS-PEI became positively charged and interacted strongly with the negatively charged sulfonate residues, exhibiting the increase of the UCST phase transition temperature.