Inspired by the increasing popularity of poly(2-ethyl-2-oxazoline) (PEtOx) for biomedical applications, this study reports the complete and thorough solution analysis of the homologous series of biocompatible PEtOx samples in a very broad range of molecular weights ranging from 11.2 × 10³ g mol⁻¹ up to 260 × 10³ g mol⁻¹. The main focus of the research was on the determination of the conformational properties of PEtOx macromolecules at a temperature of 37 °C in phosphate buffered saline (PBS) simulating the parameters of physiological media. The polymers were studied in PBS solutions by analytical ultracentrifugation, dynamic light scattering (DLS), translational diffusion, and intrinsic viscosity measurements in a temperature range from 15 °C up to 72 °C. The complete set of Kuhn–Mark–Houwink–Sakurada scaling relationships revealed linear trends over the whole range of the studied molar masses, while the determined scaling indices at 37 °C correspond to the coil conformation in a thermodynamically good solvent ([η] = 0.045 × M^0.62, s₀ = 0.010 × M^0.46 and D₀ = 1750 × M^−0.54). Based on the intrinsic viscosity values (most sensitive characteristic to the size variations of polymer coils, [η] ∼ r³), it was demonstrated that PEtOx macromolecules in PBS solutions undergo a transition from swollen polymer coils with gradual deterioration of thermodynamic quality of solutions within the temperature range of 15–45 °C, reaching θ-conditions at 55 °C with further precipitation at 62–72 °C. Also, to the best of our knowledge, the conformational parameters (equilibrium rigidity/the Kuhn segment length and the diameter of the polymer chain) of PEtOx macromolecules were evaluated under physiological conditions for the first time and constitute A = 1.8 ± 0.3 nm and d = 0.7 ± 0.4 nm. These equilibrium rigidity values classify PEtOx as a flexible macromolecule with rigidity similar to that of poly(ethylene glycol). For the first time, we were able to demonstrate a direct influence of thermosensitivity on the rigidity of the biocompatible polymer: PEtOx. The Kuhn segment length is undoubtedly decreasing when approaching the LCST.

Comparative analysis of the methods for determination of the intrinsic viscosity of both neutral and polyelectrolyte molecules is made.

In-depth characterization of pharmaceutically relevant polymers plays a pivotal role in many areas, including nanoscience, gene therapy, analytical and polymer chemistry etc. Notwithstanding substantial efforts spent in this area, there are still unresolved challenges and one of the most demanding problems is the determination of absolute molar masses of a broad range of biocompatible cationic polymers. Hereby, we present a combined analytical approach for a distinct and self-consistent characterization of a series of linear poly(ethylene imine)s (PEIs) consisting of six in-house prepared PEIs (0.9 kDa < M_theor < 250 kDa) and three commercially available linear PEIs (Polyscience labeled as 2.5 kDa, 25 kDa, and 250 kDa). The polymers were studied, in 0.2 M NaBr methanol, by the methods of molecular hydrodynamics: analytical ultracentrifugation, intrinsic viscosity and translational diffusion measurements. Absolute values of the molar masses were evaluated by the classical sedimentation-diffusion analysis resulting in the following range: 1.1 kDa < M < 13.9 kDa. It was demonstrated that the molar masses reported by the manufacturer, as well as theoretical and/or molar masses evaluated by common SEC analysis, are significantly overestimated. The complete set of Kuhn–Mark–Houwink–Sakurada scaling relations shows linear trends over the whole range of the molar masses, whilst the determined scaling indices virtually correspond to the homologous series characterized by a coil conformation ([η] = 0.255 × M^0.56; s₀ = 0.015 × M^0.48; D₀ = 994 × M^−0.52). The conformational characteristics of LPEI, i.e. equilibrium rigidity (the Kuhn segment length) and the diameter of the PEI chains, were evaluated for the first time and constitute A = 1.9 ± 0.6 nm and d = 0.4 ± 0.2 nm, respectively. The presented self-sufficient analytical approach covers an important area of thorough polymer characterization by nowadays alternative but fundamental hydrodynamic methods allowing for complete structural and molecular analysis of almost any macromolecules in solution.

Reduced-molar-mass low-acyl gellan gum was obtained by the centrifugation of an aqueous solution of commercially available food-grade gellan gum. The derived sample was characterized by NMR, FTIR, ICPE, and viscometry methods. The characteristics were compared with commercially available gellan gum Gelzan™. The main focus of the investigation is on the rheological properties of low-molar-mass-gellan ion-induced gels and the influence of reduced molar mass on gelling of gellan. The gels were prepared by adding 0.2–0.3 M of NaCl or KCl to the 0.6 g/dL gellan gum aqueous solution in a 1:1 ratio. The kinetics of gelling at room temperature, studied by rheological methods, strongly depends on molar mass and is practically independent of the temperature (up to 37 °C) and the type of ions. Analysis of the mechanical spectra characterized the obtained gels as weak gels. The gelling temperature achieved upon cooling for low-molar-mass gellan with a 0.1 M NaCl concentration was 39.0 °C (rheology) and 43.5–42.5 °C (visual observation). In summary, this study complements the existing knowledge about how the reduced molar mass of low-acyl gellan gum influences its rheological properties and gelling behavior in ion-induced systems and provides insights into the formulation of gellan-based gels, which can be effectively utilized in various food and pharmaceutical applications.