“Hard” Sphere Behavior of “Soft”, Globular-like, Hyperbranched Polyglycerols – Extensive Molecular Hydrodynamic and Light Scattering Studies

Abstract

Whether or not hyperbranched polymers behave like quasi “hard spheres” in solution is the subject of numerous fundamental discussions, also motivated by research on the perfectly branched dendrimer structures. Experimentally targeting this question, a homologous series of hyperbranched polyglycerols (HPGs) was prepared in a wide range of molar masses from ca. 3000 to 700000 g mol–1 and an overall degree of branching (DB) between 0.55 and 0.59. HPG samples have been investigated by a comprehensive set of experimental hydrodynamic and light scattering approaches, i.e., sedimentation velocity studies in analytical ultracentrifugation, dynamic and static light scattering experiments, isothermal diffusion experiments, intrinsic viscosities, and size exclusion chromatography coupled with multiangle laser light scattering. The physical soundness of the obtained average molar masses, evaluated by the different, arguably, absolute approaches to molar mass estimations was verified via the concept of the hydrodynamic invariant (A 0). The A 0 values for the here studied and literature available/calculated values for all types of branched macromolecular topologies were found to assume an average of A 0 = (2.6 ± 0.4) × 10–10 g cm2 s–2 K–1 mol–1/3. The hyperbranched polyglycerols adopt a very compact, globular-like conformation in aqueous solution, which is accompanied by a very high level of hydration, on average 1.7 g of water per 1 g of HPG macromolecules. The correspondingly determined classical scaling relationships return values that are characteristic for a classical hard sphere conformation: s = 2.16 × 10–3 M 0.67, [S], D = 251 × 10–3 M –0.33, [10–7 cm2 s–1], [η] = 5.9M 0, [cm3 g–1]. An experimentally high level of molecular compactness is then also reflected by the corresponding contraction factors, which show up to 50 times less molecular volume of HPGs at high molar mass values than their linear analogues.

Amphiphilic Diblock Copolymers Bearing Poly(Ethylene Glycol) Block: Hydrodynamic Properties in Organic Solvents and Water Micellar Dispersions, Effect of Hydrophobic Block Chemistry on Dispersion Stability and Cytotoxicity

“…Finally, a combination of hydrodynamic data allowed calculations of A 0 to give the average value equal to (2.4 ± 0.4) × 10 −10 g cm 2 s −2 K −1 mol −1/3 ( Table 5 ). This result coincides well with experimental data obtained earlier for compact non-percolated macromolecules (2.7 × 10 −10 g cm 2 s −2 K −1 mol −1/3 ) within the experimental uncertainty [ 51 , 52 , 53 , 54 ].…”

Quantification of branching within high molecular weight polymers with polyester backbones formed by transfer-dominated branching radical telomerisation (TBRT)

“…This includes studying the development of branched structures, 51 branching density 52 or calculating degree of branching 53,54 or average number of branches. 55 Techniques such as size exclusion chromatography, [56][57][58][59] light scattering 60 techniques, thermal eld-ow fractionation, 61,62 hydrolysis/ analysis 63 of branched structures and measurement using advanced nuclear magnetic resonance spectroscopy (NMR) techniques 64,65 of either the direct polymerisation product or aer post-polymerisation reaction of unreacted functional groups 66,67 have been reported for a wide range of material chemistries. The factors that confound accurate branching evaluation distribution include the overlap of critical NMR resonances and the presence of a distribution of architectures within the polymer molecular weight distribution.…”

PEG-Lipids: Quantitative Study of Unimers and Aggregates Thereof by the Methods of Molecular Hydrodynamics

“…The micelles are, thereby, characterized by a high level of hydration, averaging to as much as 4–5 g water per g of polymer material constituting the micelle (Table S2). For example, proteins, though controversially discussed in the scientific literature in instances, have average levels of hydration typically being δ = 0.36 g/g. , Hyperbranched poly­(glycerol)­s (HPGs) have much larger values of hydration, averaging to δ = 1.7 g/g, that have been explained by the solvent-permeable hyperbranched structure, i.e., water partly being present in the internal polymer architecture . In the present case, values of hydration are more than twice as large than those of HPGs underpinning the large amounts of solvent, here water, contained in and associated to the micelles assembled from about 120 individual polymer chains (Table S2).…”

“…However, it is suspected that the wide use of PEGs in our modern society is associated with undesired side effects by vaccination, the origins of these being still under debate . Next to the pharmapolymer PEG with stealth properties, alternatives have been proposed and quantitatively studied. , These include water-soluble linear pharmapolymers such as, e.g., poly­(2-alkyl-2-oxazoline)­s (POxs), , linear poly­(glycerol)­s (LPGs), ,, and hyperbranched poly­(glycerol)­s (HPGs), to mention just a few.…”