Polymer dynamics in an interface-confined space: NMR study of poly(hexyl ethacrylate)-block-poly(acrylic acid) and poly(dodecyl methacrylate)-block-poly(acrylic acid) micelles in D2O

摘要

The mobility of distant methyl side groups in poly(hexyl methacrylate)-block-poly(sodium acrylate) (PHMA-PAANa) and poly(dodecyl methacrylate))-block-poly(sodium acrylate) (PLMA-PAANa) micelles, dispersed in D2O and characterized by SANS, was studied using H-1 single and double quantum high-resolution and MAS NMR. Transverse and rotating-frame relaxation was studied at temperatures 320-345 K in the original micellar solutions and in the systems with their viscosity gradually increased by additions of high-molecular-weight poly(ethylene oxide) and with the micellar cores gradually swollen by chlorobenzene. The relaxation data were quantitatively evaluated using a pragmatic model based on Cohen-Addad's theory. The results obtained strongly indicate that the side groups are relatively immobilized to an even higher degree than in poly(2-ethylhexyl acrylate)-block-poly(acrylic acid) micelles at the same conditions. The most immobilized groups are at or near the interface. Possible underlying effects, including penetration resistance of the surrounding water molecules, fixation of the polymer backbone at the interface, and motional correlation between the distant side group and the backbone are discussed. [References: 25]