Local motions in polymeric and low molar mass supramolecular hydrogen bond assemblies: One‐ and two‐dimensional ²H‐NMR studies, full papers

Abstract

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 'H-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 C,?H,,-chain (C,,-dU4A), the packing of the single molecules is more perfect, resulting in better-defined dynamics of the molecules. The one-dimensional 'H-NMR spectra can be described quantitatively assuming a distribution of correlation times over 3 decades for the C,,-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.

Junction Dynamics in Telechelic Hydrogen Bonded Polyisobutylene Networks

“…As can be seen by comparison of the structures in Figure panels a and b, the supramolecular cluster formed by 16 U4A units resembles a layer of the t Bu-U4A single-crystal structure which was obtained from the X-ray analysis 2 Comparison of the X-ray structure of t BU−U4A 10,11 (a) and the simulated structure (top (b) and side (c) views) of a U4A cluster …”

“…We have used in the past hydrogen bond complexation to analyze the static and dynamic properties of chains with few strong interacting sites. Besides simple binary interactions, , extended junction zones may be formed in such systems. − …”

Melting of Low Molecular Weight Compounds in Confinement Observed by2H-Solid State NMR: Biphenyl, a Case Study

“…A detailed study of the pre-melting behavior would necessitate the application of the one-and two-dimensional solid state NMR methods developed over the years by the Spiess group for phenyl-group dynamics (see for example refs [84][85][86][87][88][89]), preferably on selectively 2 H or 13 C-labeled biphenyl, which is beyond the scope of the present paper.…”

Studies of chitosan. I. Preparation and characterization of chitosan/poly(vinyl alcohol) blend films

“…As network formation is a central feature of all these materials, the nature of the underlying hydrogen bond plays a central role, determining the final material properties. An early example of hydrogen‐bonded networks has been reported by the group of Stadler et al,4–9 where uradiazole moieties served as reversible crosslinks between poly(butadiene) chains generating thermoplastic materials from rubbers. Other examples that lead to a drastic change of polymer properties by the use of hydrogen‐bonding moieties mediating network formation include the use of specifically weak (diamino‐triazine/thymine,10–14 adenine/thymine,15 and cytosine/thymine15,16), strong (such as ureidopyrimidines,17–20 barbiturate/Hamilton receptor1,16,21–26), or cooperative hydrogen‐bonding moieties (such as the use of ureas in the formation of interlocked fibers,27–32 or thermoplastics33), which is especially useful in the design of self‐healing polymers 34,35.…”