| 1. |
- Björling, Mikael, et al.
(författare)
-
Conformational adaption of poly(ethylene oxide). A 13C NMR study
- 1991
-
Ingår i: Journal of Physical Chemistry. - 0022-3654. ; 95:17, s. 6706-6709
-
Tidskriftsartikel (refereegranskat)abstract
- The 13C NMR chemical shift was used as a probe for the average partition of rotational conformers around the C-C bond in the O-CH2-CH2-O segments of polyethylene oxide). Dividing the conformers into a large group of trans and a smaller group of gauche conformers, we concluded that the trans conformers have a higher (downfield) average chemical shift than the gauche conformers. The shift of the main PEO 13C line with changing environment was interpreted as an adaption in the partition between the two groups of conformers. Furthermore, the trans conformers had nonpolar character and were favored at high temperatures, whereas the gauche conformers had polar character. The measurements were compared to the predictions of a model proposed by Karlström, and a semiquantitative agreement was found.
|
|
| 2. |
- Björling, Mikael, et al.
(författare)
-
Distribution of segments for terminally attached poly(ethylene oxide) chains
- 1990
-
Ingår i: Journal of Physical Chemistry. - 0022-3654. ; 94:1, s. 471-481
-
Tidskriftsartikel (refereegranskat)abstract
- A theory for describing the equilibrium ethylene oxide (EO) segment distribution for terminally attached poly(ethylene oxide) (PEO) chains is presented. It is based on Scheutjens and Fleer's lattice model for polymer solutions in heterogeneous systems and a two-state model for the EO segments. The two-state model provides one explanation of the solubility gap of homogeneous PEO solutions. The segment distribution is examined as a function of temperature, grafting density, and curvature. The present theory predicts distributions, which cannot be reproduced with the use of temperature-dependent interaction parameters in a one-state model. Specifically, the segments tend to be more accumulated at the surface but also far away from the surface at the expense of the intervening transition region. Calculation on a model of a micelles formed by the nonionic surfactant C 12E 8 supports the experimental conclusions that the EO segments are preferentially accumulated nearby the hydrocarbon core and not completely extended into the water region.
|
|
