Interchain Hydrogen-Bonding-Induced Association of Poly(acrylic acid)- graft-poly(ethylene oxide) in Water
writer：Jinkun Hao; Guangcui Yuan;* He Cheng; Charles C. Han;,* Chi Wu
keywords：interchain hydrogen bonding, entropy
source：期刊
specific source：Macromolecules, 43, 2002-2008, 2010
Issue time：2010年
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 ofPAAandPEO(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 PAAand 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 betweenPAAandPEO 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.