Molecular Dynamics in Side‐Group Polymers with and without Liquid Crystalline Phases from ²H NMR

Abstract

Side-group liquid crystalline polymers were investigated by 1 D and 2D solid state 2H NMR methods in the glassy state. The side-group dynamics of liquid crystalline systems were compared to those of amorphous systems of the same molecular architecture. The onset of fast rotational motion of the phenylene rings additionally to phenylene flips was detected at considerably lower absolute and reduced temperature in the liquid crystalline systems indicating the influence of the ordered state on local dynamics. In 2D exchange spectra, the lineshapes are particularly sensitive towards possible slow motion of the flip axis itself which could be envisaged to fluctuate within the orientational distribution of the mesogen. However, the experimental spectra for the investigated sidegroup liquid crystalline polymers show no indication of the characteristic features, thereby proving that the flip axis is rigid within f3' even after a large number of flips.

Rigid-Rod-Like Main Chain Polymers with Rigidly Attached Chromophores: A Novel Structural Concept for Electrooptical Materials. 2. Theory and Electrooptical Measurements

“…The temperature dependence of correlation times showed clearly a locally activated Arrhenius-like behavior with activation energies in the range 42−47 kJ/mol. Similar results were obtained for the rotational motion of deuterated stilbenol NLO chromophores in the side group of electrooptic active polymers. , In rigid-rod-like aromatic polyesters, a 180° flip of the unsubstituted hydrochinone became visible in the NMR spectra above a temperature of around 260 K . Additional narrowing due to the onset of a diffusive uniaxial rotation around the para bond was observed at higher temperatures.…”

“…Similar results were obtained for the rotational motion of deuterated stilbenol NLO chromophores in the side group of electrooptic active polymers. 16,17 In rigid-rod-like aromatic polyesters, a 180°flip of the unsubstituted hydrochinone became visible in the NMR spectra above a temperature of around 260 K. 18 Additional narrowing due to the onset of a diffusive uniaxial rotation around the para bond was observed at higher temperatures. For the alkyl substituted terephthalic acid unit, no indication of a 180°flip of the phenyl ring can be deduced from the 1D-2 H-NMR spectra.…”

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.…”

Emergence of Coupled Rotor Dynamics in Metal–Organic Frameworks via Tuned Steric Interactions

“…The spectra in the range of 254 to 387 K display a superposition of the SML and FML powder patterns, with progressive increase in integrated intensity of the FML pattern with respect to the SML pattern with increasing temperature. No pattern corresponding to the IMR was detected in the entire temperature range, differing from earlier 2 H SSNMR studies on MOFs with p -phenylene rotators; ,, this is likely due to diminished intensity of IMR spectra when the rates of motion are on the order of the 2 H pattern breadths. − Furthermore, the fact that contributions from both SML and FML patterns are observed across the entire temperature range indicates the presence of a distribution of correlation times for the dynamics, which further obscures signals arising from IMR motions. ,, Such broad distributions of rotation rates are rarely found in terephthalate MOFs, ,,,− though they are more often observed for p -phenylene moieties in polymeric systems, − where structural heterogeneity among the rotors is often cited as the cause of a wide variety of rotation barriers, and consequently, rotation rates. This observation is further supported by the BDS results: there is a very broad distribution of detected frequencies for each temperature in the BDS spectra for NO 2 -MIL-53­(Al) (Figure b).…”