Interchain Hydrogen-Bonding-Induced Association of Poly(acrylic acid)-graft-poly(ethylene oxide) in Water

Abstract

Poly(acrylic acid)-graft-poly(ethylene oxide) (PAA-g-PEO) in aqueous solutions shows one fast and one slow relaxation mode in dynamic light scattering (DLS), but the mixture of PAA and PEO (PAA/PEO) in aqueous solution only has a single fast mode. The effects of pH, polymer concentration, and salt concentration on these two modes have been investigated using laser light scattering (LLS), viscometry, and rheological measurements. Our results showed that the hydrogen bonding between carboxylic group and ether oxygen led to the formation of large complexes among PAA-g-PEO chains, which were absent between PAA and PEO chains in PAA/PEO aqueous solutions. The addition of formamide can break these interchain complexes because the hydrogen bonding between formamide and PAA segment is stronger than that between PEO and PAA segment. Thermodynamically speaking, the formation of hydrogen bonds among PAA-g-PEO chains leads to a less entropy loss than that between PAA and PEO chains in PAA/PEO aqueous solution, because in the former case PEO is already chemically connected to PAA backbone. Therefore, the same enthalpy gain is sufficient to compensate the entropy loss in PAA-g-PEO aqueous solution relative to that in PAA/PEO aqueous solution, resulting in large interchain PAA-g-PEO complexes.

Quartz Crystal Microbalance Study of Ionic Strength and pH-Dependent Polymer Conformation and Protein Adsorption/Desorption on PAA, PEO, and Mixed PEO/PAA Brushes

“…Hydrogen bonds could also possibly form between PEO and PAA chains at low pH, although this was observed for high-molar-mass polymers in solution and is not easily predicted for surface-immobilized low-molar-mass polymers as found here. 46 The scheme thus aims at better describing the interface and its further interactions with proteins by showing the more probable conformations, although it is not possible to predict these conformations fully and, in particular, the PEO−PAA interactions. On the basis of the expected mixed-brush structure, the choice of adequate pH and I conditions to maximize adsorption and desorption of different proteins is facilitated without examining the whole pH−I domain experimentally.…”

Effects of Concentration and Temperature on the Dynamic Behavior of PAA-g-PEO Aqueous Solutions with Different Counterion Species: A Dielectric Spectroscopy Study

“…In addition, the results from light scattering showed that the hydrogen bonding between carboxylic group and ether oxygen led to the formation of large complexes among PAA-g-PEO chains. 24 The above fact indicated that the large complex indeed formed through the hydrogen-bonding interaction between the grafted side-chain PEO and the PAA backbone. In addition, compared to the dielectric spectra of PAA solution, the number of relaxations for the PAA-g-PEO-7% solution is one more than that for PAA solution, which shows that the new relaxation for the PAA-g-PEO-7% solution should be associated with the grafted side-chain PEO which formed the large complex.…”

“…According to the literature, 24 each PAA molecule grafted around 9.4 PEO molecules in PAA-g-PEO-7% molecules. In other words, the concentration of the complex formed by the side-chain PEO is greater than the PAA-g-PEO-7% concentration.…”

“…The interchain interaction of PAA-g-PEO in aqueous solution has been investigated using laser light scattering (LLS), viscometry, and rheological measurements. 24 But it is difficult to get more information on the dynamics and interaction, such as the electrostatic interaction between counterion and fixed charge on polyions and the fluctuation of counterions along the molecular chains, just by any individual method mentioned above but the dielectric measurement.…”

Kinetics of temperature response of PEO-b-PNIPAM-b-PAA triblock terpolymer aggregates and of their complexes with lysozyme

“…Although hydrogen bonding is strong at low pH, it may stabilize aggregated structures in a cooperative manner in neutral or even weak basic conditions. This has been shown in [21] where the PAA-g-PEO copolymer showed aggregation at high pH contrary to the mixture of linear homopolymer PAA and PEO. There, it was claimed that the entropic cost for aggregation is lower in the case of preajoined PEO segments in a PAA backbone.…”