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

The mobility of distant methyl side groups in poly(hexyl methacrylate)-bloc k-poly(sodium acrylate) (PHMA-PAANa) and poly(dodecyl methacrylate))-block- poly(sodium acrylate) (PLMA-PAANa) micelles, dispersed in D2O and character ized by SANS, was studied using H-1 single and double quantum high-resoluti on and MAS NMR. Transverse and rotating-frame relaxation was studied at tem peratures 320-345 K in the original micellar solutions and in the systems w ith their viscosity gradually increased by additions of high-molecular-weig ht poly(ethylene oxide) and with the micellar cores gradually swollen by ch lorobenzene. The relaxation data were quantitatively evaluated using a prag matic model based on Cohen-Addad's theory. The results obtained strongly in dicate that the side groups are relatively immobilized to an even higher de gree than in poly(2-ethylhexyl acrylate)-block-poly(acrylic acid) micelles at the same conditions. The most immobilized groups are at or near the inte rface. Possible underlying effects, including penetration resistance of the surrounding water molecules, fixation of the polymer backbone at the inter face, and motional correlation between the distant side group and the backb one are discussed.