| 1. |
- Bonk, Fábio A., et al.
(författare)
-
Investigation by Combined Solid-State NMR and SAXS Methods of the Morphology and Domain Size in Polystyrene-b-Polyethylene Oxide-b-Polystyrene Triblock Copolymers
- 2010
-
Ingår i: Journal of Polymer Science. Part B, Polymer Physics. - : Wiley. - 0887-6266. ; 48:1, s. 55-64
-
Tidskriftsartikel (refereegranskat)abstract
- The microphase structure of a series of polystyrene-b-polyethylene oxide-b-polystyrene (SEOS) triblock copolymers with different compositions and molecular weights has been studied by solid-state NMR, DSC, wide and small angle X-ray scattering (WAXS and SAXS). WAXS and DSC measurements were used to detect the presence of crystalline domains of polyethylene-oxide (PEO) blocks at room temperature as a function of the copolymer chemical composition. Furthermore, DSC experiments allowed the determination of the melting temperatures of the crystalline part of the PEO blocks. SAXS measurements, performed above and below the melting temperature of the PEO blocks, revealed the formation of periodic structures, but the absence or the weakness of high order reflections peaks did not allow a clear assessment of the morphological structure of the copolymers. This information was inferred by combining the results obtained by SAXS and 1H NMR spin diffusion experiments, which also provided an estimation of the size of the dispersed phases of the nanostructured copolymers.
|
|
| 2. |
- Faria, Gregorio C., et al.
(författare)
-
A Multitechnique Study of Structure and Dynamics of Polyfluorene Cast Films and the Influence on Their Photoluminescence
- 2009
-
Ingår i: The Journal of Physical Chemistry Part B. - : American Chemical Society (ACS). - 1520-5207 .- 1520-6106. ; 113:33, s. 11403-11413
-
Tidskriftsartikel (refereegranskat)abstract
- This article describes the microstructure and dynamics in the solid state of polyfluorene-based polymers, poly(9,9-dioctylfluorenyl-2,7-diyl) (PFO), a semicrystalline polymer, and poly[(9,9-dioctyl-2,7-divinylene-fluorenylene)-alt-co-{2-methoxy-5-(2-ethyl-hexyloxy)-1,4-phenylene vinylene}, a copolymer with mesomorphic phase properties. These structures were determined by wide-angle X-ray scattering (WAXS) measurements. Assuming a packing model for the copolymer structure, where the planes of the phenyl rings are stacked and separated by an average distance of 4.5 Å and laterally spaced by about 16 Å, we followed the evolution of these distances as a function of temperature using WAXS and associated the changes observed to the polymer relaxation processes identified by dynamical mechanical thermal analysis. Specific molecular motions were studied by solid-state nuclear magnetic resonance. The onset of the side-chain motion at about 213 K (β-relaxation) produced a small increase in the lateral spacing and in the stacking distance of the phenyl rings in the aggregated structures. Besides, at about 383 K (α-relaxation) there occurs a significant increase in the amplitude of the torsion motion in the backbone, producing a greater increase in the stacking distance of the phenyl rings. Similar results were observed in the semicrystalline phase of PFO, but in this case the presence of the crystalline structure affects considerably the overall dynamics, which tends to be more hindered. Put together, our data explain many features of the temperature dependence of the photoluminescence of these two polymers.
|
|
