ISSN:
0323-7648
Keywords:
Chemistry
;
Polymer and Materials Science
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
,
Physics
Notes:
Supramolecular structures based on 4-(3,5-dioxo-1,2,4-triazolidin-4-yl) benzoic acid (U4A) units act as effective junction zones in functionalized polybutadienes, resulting in the formation of thermoplastic elastomers. The dynamics on a molecular scale of the phenyl rings have been probed by 2H-NMR. In the polymeric system, there are three spatially separated environments, which are reflected in the mobility of the polar units. Phenyl rings which are incorporated in the structures are either rigid or undergo 180° phenyl flips. The small fraction of free functional groups move isotropically and their mobility is coupled to the dynamics of the polybutadiene matrix. In two model compounds, where the polymer backbone is replaced by a 1-butenyl (tBu-dU4A) or a C12H24-chain (C12-dU4A), the packing of the single molecules is more perfect, resulting in better-defined dynamics of the molecules. The one-dimensional 2H-NMR spectra can be described quantitatively assuming a distribution of correlation times over 3 decades for the C12-dU4A and 2 decades for the tBu-dU4A, respectively. From the average jump rates the activation energies are determined as 101 kJ/mol and 102 kJ/mol. The geometry of the motional processes is defined by the environment in the clusters up to the order-disorder transition temperature as determined by DSC. The two-dimensional spectra of the model compounds show an elliptical exchange pattern, indicating well-defined slow 180° phenyl flips on a time scale of 100 ms up to 3 s.
Additional Material:
15 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/actp.1995.010460402
Permalink
