Dextran‐Based Polycations: Thermodynamic Interaction with Water as Compared With Unsubstituted Dextran, 1 – Volumetric Properties and Light Scattering

Abstract

Dextran and random dextran‐based copolymers containing different molar fractions f of charged units are studied in aqueous solution and in the pure state. The specific volumes of the solutions decrease linearly with increasing weight fraction of the polymer. Extrapolation to the pure state yields information on the hypothetical liquid polymers, exhibiting a pronounced minimum at f ≈ 0.1. A similar dependence is also observed for the pure solid polymers; however, the specific volumes at low f are considerably larger and at high f are slightly smaller. These differences are discussed in terms of the non‐equilibrium structures formed during sample preparation. The thermal expansivities of the solutions pass through a maximum at f ≈ 0.1. Light scattering shows that the thermodynamic quality of water has a minimum at f ≈ 0.1.magnified image

Dextran‐Based Polycations: Thermodynamic Interaction with Water as Compared With Unsubstituted Dextran, 2 – Flory/Huggins Interaction Parameter

“…Light-scattering experiments performed with the present polymers are reported in the previous part of the present publication, [5] primarily dealing with the changes in the volumetric properties of the aqueous solutions resulting from the transition of neutral polymer to polyelectrolyte. The scattering experiments were required to obtain direct information on the Flory-Huggins interaction parameter in the limit of high dilution, which is inaccessible from vapor-pressure measurements.…”

“…Its validity is only checked after the evaluation in retrospect. There are two options for the data treatment: either the primary data are converted into composition-dependent x values by means of Equation 5 and the system-specific parameters are adjusted according to Equation 4, or another possibility makes use of Equation 8, resulting from inserting x from Equation 4 into Equation 5 and rearrangement, to obtain the composition dependence of the vapor pressures:…”

“…In most cases, the differences in the system-specific parameters of Equation 4 obtained on the basis of w or w remain within the experimental errors. Figure 5-7 show the corresponding composition dependencies of the Flory-Huggins interaction parameters calculated from the reduced vapor pressures according to Equation 5 in combination with the x o values resulting from the light-scattering measurements, [5] as described above. Table 1) have been shifted by the constant a.…”

“…Vapor-pressure data are presented in this work; the corresponding light-scattering results are reported and discussed in the previous contribution (Part 1 of this paper). [5] The current findings will be evaluated and discussed in the light of the aforementioned approach, together with the sparse information on the interaction between polyelectrolytes and water in the absence of an external salt that has been reported in the literature.…”

Thermosensitive Poloxamer-graft-Carboxymethyl Pullulan: A Potential Injectable Hydrogel for Drug Delivery

“…In addition, a shift of the ester absorption band from 1735 to 1739 cm −1 is observed, as well as the appearance of absorption bands specific to the amide bond (1635 cm −1 (C=O, amide I), 1554 cm −1 (coupling NH and CN, amide II) and 1450 cm −1 (C-N stretch, amide III)), which demonstrates the coupling of poloxamer to the carboxymethyl pullulan chain through an amide bond. The density of the grafted polymer measured by the pycnometry method [59] in tetrahydrofuran (THF) at 25 °C, is 1.336 g/cm 3 and it remains soluble in water and polar solvents (dimethylfuran (DMF), dimethyl sulfoxide (DMSO), etc. ), and insoluble in THF, ethyl ether, and chloroform.…”