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Solution Properties and Potential Biological Applications of Zwitterionic Poly(ε-N-methacryloyl-l-lysine)
2013
Poly(e-N-methacryloyl-l-lysine) (PMALys) was synthesized by free radical polymerization yielding a zwitterionic polymer with Mw = 721 000 g mol–1. The polymer dissolves in pure water as well as in aqueous salt solution up to 5 M NaClO4 and over wide range of pH values (1.3 ≤ pH ≤ 12.7) as single chains without any sign for aggregate formation. The zwitterionic polymer shows an expanded random coil structure at and close to isoelectric conditions and further expands upon addition of acid and base, respectively. The polymer fulfills four major prerequisites for a promising nano carrier in potential biomedical applications: (1) It is biocompatible, indicated by a low cytotoxicity. (2) It does …
Isobaric Vapor−Liquid Equilibria for Water + Acetic Acid + Sodium Acetate
2003
Isobaric vapor−liquid equilibria for the binary water + sodium acetate and acetic acid + sodium acetate systems and ternary mixtures of water, acetic acid, and sodium acetate have been measured at 100 kPa with a recirculating still. The addition of sodium acetate to water + acetic acid mixtures produced an appreciable rise in equilibrium temperature but a small effect on the relative volatility of water, which was augmented at higher water solvent concentrations and decreased at lower concentrations. These effects increased with higher salt concentrations. The experimental binary data sets have been correlated using a modified Mock's electrolyte NRTL model, which takes into account the asso…
Revisiting Secondary Structures in NCA Polymerization: Influences on the Analysis of Protected Polylysines
2014
Two series (degree of polymerization: 20–200) of polylysines with Z and TFA protecting groups were synthesized, and their behavior in a range of analytical methods was investigated. Gel permeation chromatography of the smaller polypeptides reveals a bimodal distribution, which is lost in larger polymers. With the help of GPC, NMR, circular dichroism (CD), and MALDI-TOF, it was demonstrated that the bimodal distribution is not due to terminated chains or other side reactions. Our results indicate that the bimodality is caused by a change in secondary structure of the growing peptide chain that occurs around a degree of polymerization of about 15. This change in secondary structure interferes…
Polymer solutions confined in slit-like pores with attractive walls: An off-lattice Monte Carlo study of static properties and chain dynamics
1996
Using a bead spring model of flexible polymer chains, the density profiles and chain configurational properties of polymer solutions confined between parallel plates were studied. A wide range of density ϕ, chain length N, and strength e of a short-range attractive wall potential was investigated. Both a temperature T in the good solvent regime (T > θ, θ being the Theta temperature where a chain in unconfined bulk three-dimensional solution would behave ideally) and a temperature in the bad solvent regime (T θ) show a crossover from two-dimensional excluded volume behavior (Rg ∝ N2ν with ν = 3/4) to ideal random walk behavior (ν = 1/2), the relaxation times show effective exponents Zeff (τ …
Modelling small angle neutron scattering data from polymers in supercritical fluids
2000
In this paper we report a SANS investigation of micelle formation by fluorocarbon-hydrocarbon block copolymers in supercritical CO2(scCO2) at 313K. A sharp unimer-micelle transition is obtained due to the tuning of the solvating ability of scCO2 by profiling pressure. At high pressure the copolymer is in a monomeric state with a random coil structure. By lowering the pressure aggregates are formed with the hydrocarbon segments forming the core and the fluorocarbon segments forming the corona of spherical aggregates. This aggregate-unimer transition is driven by the gradual penetration of CO2 molecules toward the core of the aggregate and is critically related to the density of the solvent, …
Isobaric Vapor−Liquid Equilibria for Binary and Ternary Mixtures with Cyclohexane, Cyclohexene, and Methyl Isobutyl Ketone at 100 kPa
2010
Consistent vapor−liquid equilibrium (VLE) data at 100 kPa have been determined for the ternary system cyclohexane + cyclohexene + methyl isobutyl ketone and two constituent binary systems: cyclohexane + methyl isobutyl ketone and cyclohexene + methyl isobutyl ketone. Both binary systems show positive deviations from ideal behavior and do not present an azeotrope. The VLE data have been correlated by the Wilson, UNIQUAC, and NRTL equations. The ternary system does not present an azeotrope and is well predicted from binary interaction parameters. Prediction with the UNIFAC method has also been obtained.
A Precursor Route to Supramolecular Oligo(p-phenylene terephthalamide) Block Copolymers
2008
New soluble precursors for the step-wise synthesis of oligo(p-phenylene terephthalamide) block copolymers are described. Kevlar-like aramide oligomers up to the hexamer (six phenyl groups) were prepared in a polymer-analogous manner. Activating the carboxylic-acid-carrying oligomers as carbonyl chlorides while reversibly transforming the aromatic amides into imidoyl chlorides gave access to soluble precursors. The dimer and tetramer precursor were prepared and used in block copolymer synthesis. Single-crystal XRD confirmed the structure of the dimer precursor. Above a critical rod length, the Kevlar-like rod-coil block copolymers show strong aggregation in non-polar solvents such as chlorof…
Random-strain-field effects on the low-temperature state of KCN
1991
Random strain fields have been introduced into samples of KCN by pressing pellets from powder and by thermal cycling. X-ray diffractograms show that the low-temperature structure depends strongly on the sample history. In some cycles the noncubic low-temperature phases have been suppressed in mesoscopic surface regions of the samples and the quadrupolar-glass state formed instead.
Mapping onto ideal chains overestimates self-entanglements in polymer melts
2017
In polymer physics it is typically assumed that excluded volume interactions are effectively screened in polymer melts. Hence, chains could be described by an effective random walk without excluded volume interactions. In this letter, we show that this mapping is problematic by analyzing the occurrence of knots, their spectrum and sizes in polymer melts, corresponding random walks and chains in dilute solution. The effective random walk severely overrates the occurrence of knots and their complexity, particularly when compared to melts of flexible chains, indicating that non-trivial effects due to remnants of self-avoidance still play a significant role for the chain lengths considered in t…
Molecular motion, thermal expansion, and phase transitions in paraffins: A model for polymers
2007
Owing to their simple chemical structure paraffins are generally regarded as representing a system which is especially suitable for a model study of the thermal behavior of oligomeric and polymeric solids. Extensive investigations on the properties of n-tritriacontane (C33H68) provide an example. For this system an identification of several types of motional mechanisms become possible. Their presence leads to peculiarities in the thermal expansion and to the occurrence of solid-solid phase transitions. Paraffins and polyethylene exhibit a marked anisotropy in the lateral thermal expansion. An analysis of the molecular background can be based on a modified Gruneisen theory which connects exp…