POx as an Alternative to PEG? A Hydrodynamic and Light Scattering Study

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(2-oxazoline)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.