Poly(ethylene glycol)s (PEG) are widely and intensely used in the pharmaceutical industry and biomedical applications, and due to this fact, antibodies have recently been reported. Poly(2oxazoline)s (POx) are promising candidates for potential replacement of PEG in related applications, and as such, their hydrodynamic properties and characteristics derived from light scattering experiments are important to reconcile their behavior in solution. In this study, we have investigated the molecular hydrodynamic characteristics of poly(2-methyl-2-oxazoline)s and poly(2-ethyl-2-oxazoline)s in the pharmaceutical molar mass range as base candidates for such applications, prepared by cationic ring-opening polymerization in a microwave reactor. A combined viscometry and sedimentation−diffusion analysis by using sedimentation velocity experiments in an analytical ultracentrifuge includes (i) the study of intrinsic viscosities, (ii) sedimentation coefficients, and (iii) derived translational diffusion coefficients. These characteristics are then interrelated through hydrodynamic invariants that showed consistency between all these hydrodynamic parameters and, consequently, adequate values of derived absolute molar masses. The established scaling relationships of POx could as well be related quantitatively to that of pharmaceutical PEG from a recent study. Complementary, the molar masses were estimated by asymmetrical flow field-flow fractionation (AF4) and size exclusion chromatography (SEC) in conjunction with multiangle laser light scattering (MALLS). Thus, the obtained results of molar masses show an overarching good correlation to that of the hydrodynamic analysis utilizing the ultracentrifuge and viscometry. However, we demonstrate as well that AF4-/SEC-MALLS experiments of macromolecules below 10 000 g mol −1 may provide erroneous information on their molar mass, identified and discussed by the hydrodynamic invariant concept interrelating three independent experimental approaches on the same sample, i.e., (i) intrinsic viscosities, (ii) intrinsic sedimentation coefficients, and (iii) molar masses from light scattering. Our results open the gate for the replacement of pharmaceutical PEG by POx on a physicochemical basis with key first-principles hydrodynamic parameters of interest, all associated with values of the molar mass.

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The solution behavior originating from molecular characteristics of synthetic macromolecules plays a pivotal role in many areas, in particular the life sciences. This situation necessitates the use of complementary hydrodynamic analytical methods as the only means for a complete structural understanding of any macromolecule in solution. To this end, we present a combined hydrodynamic approach for studying in-house prepared, low dispersity poly(ethylene glycols)s (PEGs), also known as poly(ethylene oxide)s (PEOs) depending on the classification used, synthesized from varying initiation sites by the living anionic ring opening polymerization. The series of linear PEGs in the molar mass range of only a few thousand to 50 000 g mol have been studied in detail via viscometry and sedimentation-diffusion analysis by analytical ultracentrifugation. The obtained estimations for intrinsic viscosity, diffusion coefficients, and sedimentation coefficients of the macromolecules in the solution-based analysis clearly showed self-consistency of the followed hydrodynamic approach. This self-consistency is underpinned by appropriate and physically sound values of hydrodynamic invariants, indicating adequate values of derived absolute molar masses. The classical scaling relations of Kuhn-Mark-Houwink-Sakurada of all molar-mass dependent hydrodynamic estimates show linear trends, allowing for interrelation of all parametric macromolecular characteristics. Differences among these are ascribed to the observation of α-end and chain-length dependent solvation of the macromolecules, identified from viscometric studies. This important information allows for analytical tracing of variations of scaling relationships and a physically sound estimation of hydrodynamic characteristics. The demonstrated self-sufficient methodology paves an important way for a complete structural understanding and potential replacement of pharmaceutically relevant PEGs by alternative macromolecules offering a suite of similar or tractably distinct physicochemical properties.

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