Search results for "solu"
showing 10 items of 7577 documents
Thermodynamics of Aqueous Poly(ethylene oxide)−Poly(propylene oxide)−Poly(ethylene oxide)/Surfactant Mixtures. Effect of the Copolymer Molecular Weig…
2004
A calorimetric study was performed to focus attention on the interactions between copolymers and anionic surfactants in aqueous solutions. Three aspects were analyzed: (1) the hydrophobicity of the surfactant, (2) the change of the copolymer molecular weight, and (3) the nature of the hydrophilicity of the copolymer. To this purpose, the family of sodium alkanoates (sodium octanoate through sodium dodecanoate) and the triblock copolymers EO76PO 29EO76 (F68), EO103PO39EO 103 and EO132PO50EO132 were investigated. Comparing F68 and EO13PO30EO13 (L64), previously studied by us, provided information on the effect of the copolymer hydrophilicity. The experimental data were analyzed by means of a …
Hyperbranched Poly(propylene oxide): A Multifunctional Backbone-Thermoresponsive Polyether Polyol Copolymer
2012
Backbone-thermoresponsive hyperbranched poly(propylene oxide)-based polyether polyols have been synthesized by anionic ring-opening copolymerization of glycidol and propylene oxide. The number of functional hydroxyl end groups and the lower critical solution temperature (LCST) can be readily adjusted by varying the comonomer ratio. Molecular weights in the range of 1200-2000 g/mol were achieved. Hyperbranched polyether polyols with LCST values between 24 and 83 °C can be obtained in a convenient one-step reaction.
PolyAT chemical denaturation in w/o microemulsion
2004
CD and UV spectroscopies have been used to investigate the effects caused by the addition of either strong acid-or base-containing microemulsions on the behaviour of the synthetic polynucleotide polyAT entrapped in the aqueous core of a cationic quaternary water-in-oil microemulsion (μE). The titrations were performed in the presence of variable concentrations of NaCl, in the range 0.00 to 0.60 M. In both cases, the primary effect was the reversible transition from B-double helix to random coil of the guest polynucleotide. However, in the microemulsive medium, the number of moles of protons (RH) and hydroxide ions (ROH) per mole of titrable sites are independent of the salt concentration bu…
Switchable Supramolecular Crosslinking of Cyclodextrin-Modified Hyperbranched Polyethylenimine via Anthraquinone Dyes
2011
Two anthraquinone dyes, 5,8-di-N-adamantylamino-1,4-dihydroxyanthraquinone (AQ-OH) and 1,4-di-N-adamantylaminoanthraquinone (AQ-H), are synthesized. The combination of AQ-OH and AQ-H with hyperbranched polyethylenimine (PEI) bearing covalently attached β-cyclodextrin spontaneously formed host–guest complexes with hydrodynamic diameters of about 260 nm. Even enlarged structures of the trifunctional AQ-H were observed via DLS. Repeated measurements show that their assembly and disassembly is reversible with a critical point at 26 °C and therefore switchable via temperature. Also superstructures up to 100 μm were detected via TEM, cryo-TEM-, and SEM. Hence, a smart colored network of switchabl…
Towards storage-stable high-content recycled tyre rubber modified bitumen
2018
The addition of crumb rubber particles as bitumen modifier can be currently considered as a well-established alternative to conventional polymers for bitumen modification. However, Recycle Tyre Rubber (RTR) modified binders still present drawbacks such as poor mix workability and hot storage stability. Within this study the authors try unlocking the full potential of devulcanised tyre rubber-heavy oils blend, named Liquid Rubber (LR), by exploring the possibility of tailoring recycled polymer modified bitumen with unconventional high-content of RTR and designed to overcome the above mentioned technological problems of RTR modified bitumen while keeping its advantages. Results show that LR-b…
Poly(S-ethylsulfonyl-l-homocysteine): An α-Helical Polypeptide for Chemoselective Disulfide Formation
2018
Homocysteine and cysteine are the only natural occurring amino acids that are capable of disulfide bond formations in peptides and proteins. The chemoselective formation of asymmetric disulfide bonds, however, is chemically challenging and requires an activating group combining stability against hard nucleophiles, e.g., amines, with reactivity toward thiols and soft nucleophiles. In light of these considerations, we introduced the S-alkylsulfonyl cysteines in our previous work. Here, we present the synthesis and ring-opening polymerization of S-ethylsulfonyl-l-homocysteine N-carboxyanhydrides. We demonstrate that the polymerization leads to narrowly distributed polypeptides (Đ = 1.1–1.3) wi…
Evidence for chain transfer in the atom transfer radical polymerization of butyl acrylate
2000
Poly(butyl acrylate) (PBuA) of high molecular weight was synthesized by atom transfer radical polymerization (ATRP) in ethyl acetate. Whereas for low molecular weight polymers, a linear increase of the number-average molecular weight. M n , versus conversion and narrow molecular weight distributions indicate the suppression of side reactions, a downward curvature in the plot of M n versus conversion was observed for high molecular weights (M n > 50 000). This effect is explained by chain transfer reactions, leading to branched polymers. GPC measurements with a viscosity detector give evidence for the branched structure of high molecular weight polymers obtained in ATRP. In addition, transfe…
Intrinsic viscosities of polyelectrolytes in the absence and in the presence of extra salt: Consequences of the stepwise conversion of dextran into a…
2011
Abstract Viscosities of dilute polymer solutions were measured in capillary viscometers for samples varying in their fraction f of charged units from 0.00 to 0.90. The dependence of the logarithm of the relative viscosity on polymer concentration c is in all cases reproduced quantitatively by three characteristic parameters: [ η ], the intrinsic viscosity; B , a viscometric interaction parameter (related to the Huggins constant); [ η ] , a parameter required only for polyelectrolytes at low concentrations of extra salt. In pure water [ η ] increases more than 80 times as the fraction f rises from zero to 0.90 and [ η ] starts from zero and goes up to ≈71 mL/g. Upon the addition of NaCl [ η …
Stimuli-responsive brushes with active minority components: Monte Carlo study and analytical theory
2015
Using a combination of analytical theory, Monte Carlo simulations, and three dimensional self-consistent field calculations, we study the equilibrium properties and the switching behavior of adsorption-active polymer chains included in a homopolymer brush. The switching transition is driven by a conformational change of a small fraction of minority chains, which are attracted by the substrate. Depending on the strength of the attractive interaction, the minority chains assume one of two states: An exposed state characterized by a stem-crown-like conformation, and an adsorbed state characterized by a flat two-dimensional structure. Comparing the Monte Carlo simulations, which use an Edwards-…
A procedure for predicting sorption equilibrium in ternary polymer systems from Flory–Huggins binary interaction parameters and the inversion point o…
1989
A procedure has been developed, based on the Flory–Huggins theory as generalized by Pouchlý, which permits the calculation of preferential (λ) and total (Y) sorption coefficients from previous information on the binary interaction parameters, χ, χ, and g12(ϕ10) and on the mixture composition at which the sign of λ inverts. The expressions obtained were applied to 10 cosolvent polymer systems for which experimental values of λ and Y are known. Practically in all the studied systems, the theoretical predictions are in fair accordance with the experimental data.