Poly(ethylene oxide)- and poly (acrylamide)-based water-soluble associative polymers: synthesis, characterisation, properties in solution

Tailoring Waterborne Coating Rheology with Hydrophobically Modified Ethoxylated Urethanes (HEURs): Molecular Architecture Insights Supported by CG-MD Simulations

A novel investigation of the effects of the hydrophilic and hydrophobic segments of hydrophobically modified ethoxylated urethanes (HEURs) on the rheological properties of their aqueous solutions, latex-based emulsions, and waterborne paints is demonstrated. Different HEUR thickeners were produced by varying the poly(ethylene glycol) (PEG) molecular weight and terminal hydrophobic size. Results reveal that the strength of hydrophobic associations and, consequently, the rheological properties of HEUR formulations can be effectively controlled by modifying the structure of the hydrophobic segment, specifically, the combination of diisocyanate and monoalcohol. This allows for the on-demand attainment of diverse rheological behaviors ranging from predominantly Newtonian profiles exhibiting lower viscosities to markedly pseudoplastic behaviors with significantly higher viscosities. The length of the hydrophilic group appears to affect viscosity only marginally up to a molecular weight of 23,000 g/mol, with more notable effects at 33,000 g/mol. Additionally, it was indicated that the rheological responses observed in water solutions provide a reliable forecast of their behavior in latex-based emulsions and waterborne paints. Coarse-grained molecular dynamics (CG-MD) simulations were also applied to gain insight into HEUR micelle dynamics in aqueous solutions. Guided by the DBSCAN algorithm, the simulations successfully captured the concentration-dependent behavior and the impact of hydrophilic chain length, aligning with the experimental viscosity trends. Various metrics were employed to provide a comprehensive analysis of the micellization process, including the hydrophobic cluster volume, the total micellar volume, the aggregation number, and the number of chains interconnecting with other micelles.

Atomic Force Microscopy of Hydrolysed Polyacrylamide Adsorption onto Calcium Carbonate

In this work, the interaction of hydrolysed polyacrylamide (HPAM) of two molecular weights (F3330, 11-13 MDa; F3530, 15-17 MDa) with calcium carbonate (CaCO3) was studied via atomic force microscopy (AFM). In the absence of polymers at 1.7 mM and 1 M NaCl, good agreement with DLVO theory was observed. At 1.7 mM NaCl, repulsive interaction during approach at approximately 20 nm and attractive adhesion of approximately 400 pN during retraction was measured, whilst, at 1 M NaCl, no repulsion during approach was found. Still, a significantly larger adhesion of approximately 1400 pN during retraction was observed. In the presence of polymers, results indicated that F3330 displayed higher average adhesion (450-625 pN) and interaction energy (43-145 aJ) with CaCO3 than F3530's average adhesion (85-88 pN) and interaction energy (8.4-11 aJ). On the other hand, F3530 exerted a longer steric repulsion distance (70-100 nm) than F3330 (30-70 nm). This was likely due to the lower molecular weight. F3330 adopted a flatter configuration on the calcite surface, creating more anchor points with the surface in the form of train segments. The adhesion and interaction energy of both HPAM with CaCO3 can be decreased by increasing the salt concentration. At 3% NaCl, the average adhesion and interaction energy of F3330 was 72-120 pN and 5.6-17 aJ, respectively, while the average adhesion and interaction energy of F3530 was 11.4-48 pN and 0.3-2.98 aJ, respectively. The reduction of adhesion and interaction energy was likely due to the screening of the COO- charged group of HPAM by salt cations, leading to a reduction of electrostatic attraction between the negatively charged HPAM and the positively charged CaCO3.

Phenanthroline-A Versatile Ligand for Advanced Functional Polymeric Materials

The controlled incorporation of phenanthroline moieties into polymers is introduced, demonstrating their application as metal-ion complexing ligands for the construction of advanced macromolecular structures. Specifically, two phenanthroline-containing monomers based on acrylate and styrene functionalities, were synthesized. Each monomer was readily copolymerized with either N,N-dimethylacrylamide or styrene via nitroxide-mediated polymerization, resulting in narrowly distributed polar or non-polar copolymers. To demonstrate the versatility of the established polymer systems, the polar polymer was employed for transition metal induced single-chain nanoparticle formation, verified by diffusion-ordered NMR and UV/Vis spectroscopy. Furthermore, the non-polar polymer allows facile incorporation of lanthanide ions, creating luminescent metallo-polymers, in-depth characterized by advanced photophysical experiments and 2D NMR measurements.

Multiscale Molecular Dynamics Simulations of Model Hydrophobically Modified Ethylene Oxide Urethane Micelles

The flower-like micelles of various aggregation numbers of a model hydrophobically modified ethylene oxide urethane (HEUR) molecule, C16E45C16, and their corresponding starlike micelles, containing the surfactants C16E22 and C16E23, were studied by atomistic and coarse-grained molecular dynamic (MD) simulations. We used free energies from umbrella sampling to calculate the size distribution of micelle sizes and the average time for escape of a hydrophobic group from the micelle. Using the coarse-grained MARTINI force field, the most probable size of the model HEUR molecule was thereby determined to be about 80 hydrophobes per micelle and the average hydrophobe escape time to be about 0.1 s, both of which are consistent with previous experimental studies. Atomistic simulations reveal that hydrogen bond formation and the mean lifetime of hydration waters of the poly(ethylene oxide) (or PEO) groups are location-dependent in the HEUR micelle, with PEO groups immediately adjacent to the C16 groups forming the fewest hydrogen bonds with water and having hydration waters with longer lifetimes than those of the PEO groups located further away from the C16 groups.

Phase behavior of flowerlike micelles in a SCF cell model

We study the interactions between flowerlike micelles, self-assembled from telechelic associative polymers, using a molecular self-consistent field (SCF) theory and discuss the corresponding phase behavior. In these calculations we do not impose properties such as aggregation number, micellar structure and number of bridging chains. Adopting a SCF cell model, we calculate the free energy of interaction between a central micelle surrounded by others. Based on these results, we predict the binodal for coexistence of dilute and dense liquid phases, as a function of the length of the hydrophobic and hydrophilic blocks. In the same cell model we compute the number of bridges between micelles, allowing us to predict the network transition. Several quantitative trends obtained from the numerical results can be rationalized in terms of transparent scaling arguments.

Tumor pH-responsive flower-like micelles of poly(L-lactic acid)-b-poly(ethylene glycol)-b-poly(L-histidine)

Polymeric micelles were constructed from poly(l-lactic acid) (PLA; M(n) 3K)-b-poly(ethylene glycol) (PEG; M(n) 2K)-b-poly(l-histidine) (polyHis; M(n) 5K) as a tumor pH-specific anticancer drug carrier. Micelles (particle diameter: approximately 80 nm; critical micelle concentration (CMC): 2 microg/ml) formed by dialysis of the polymer solution in dimethylsulfoxide (DMSO) against pH 8.0 aqueous solution, are assumed to have a flower-like assembly of PLA and polyHis blocks in the core and PEG block as the shell. The pH-sensitivity of the micelles originates from the deformation of the micellar core due to the ionization of polyHis at a slightly acidic pH. However, the co-presence of pH-insensitive lipophilic PLA block in the core prevented disintegration of the micelles and caused swelling/aggregation. A fluorescence probe study showed that the polarity of pyrene retained in the micelles increased as pH was decreased from 7.4 to 6.6, indicating a change to a more hydrophilic environment in the micelles. Considering that the size increased up to 580 nm at pH 6.6 from 80 nm at pH 7.4 and that the transmittance of micellar solution increased with decreasing pH, the micelles were not dissociated but rather swollen/aggregated. Interestingly, the subsequent decline of pyrene polarity below pH 6.6 suggested re-self-assembly of the block copolymers, most likely forming a PLA block core while polyHis block relocation to the surface. Consequently, these pH-dependent physical changes of the PLA-b-PEG-b-polyHis micelles provide a mechanism for triggered drug release from the micelles triggered by the small change in pH (pH 7.2-6.5).

Bile Acids as Building Blocks of Amphiphilic Polymers. Applications and Comparison with Other Systems

This review deals with the use of bile acids as building blocks of amphiphilic polymers. These natural polyfunctional organic molecules have been employed in the synthesis of macromolecules combining hydrophilic and hydrophobic sequences. The two main synthetic strategies are radical (co)polymerization after attachment of a vinyl group onto the bile acid and molecule grafting of bile acid onto a hydrophilic polymer. The physicochemical properties of the resulting polymers both as bulk materials and in aqueous solution are reviewed and compared with polymers of other structures. Whenever possible, semiquantitative correlations are established and discussed.