Chain rotation

In a real polymer chain, rotation around backbone bonds is likely to be hindered by a potential energy barrier of height AEr. If AEr < RT, the population of the... 

Cross Polarization — Magic Angle Sample Spinning NMR Studies. With Respect to the Rotational Isomeric States of Saturated Chain Molecules of Aliphatic Chain Rotational Isomers... 

Fig. 5 Schematic representation of the domain contributions to the tensile deformation of the fibre chain stretching and chain rotation due to shear deformation...

In addition to the above effects, the intermolecular interaction may affect polymer dynamics through the thermodynamic force. This force makes chains align parallel with each other, and retards the chain rotational diffusion. This slowing down in the isotropic solution is referred to as the pretransition effect. The thermodynamic force also governs the unique rheological behavior of liquid-crystalline solutions as will be explained in Sect. 9. For rodlike polymer solutions, Doi [100] treated the thermodynamic force effects by adding a self-consistent mean field or a molecular field Vscf (a) to the external field potential h in Eq. (40b). Using the second virial approximation (cf. Sect. 2), he formulated Vscf(a), as follows [4] ... 

Fig. 23. Crystal structure of /Worm (modification-/) poly (vinylidene fluoride). Figures in broken lines represent chain rotation to avoid the steric hindrance between F atoms (Hasegawa and others, 1970)...

After Ala, residues with long side chains exhibit higher tendencies to form helices due to possible position-dependent, side-chain interactions that are helix stabilizing, such as salt bridges and hydrogen bonding. However, aromatic or ((-branched side chains act as helix breakers in monomeric peptides due to constraints on side-chain rotational entropy when in an a-helical conformation/11,14 201... 

Side-Chain Rotations About the Bonds Linking Side Chains to the Main... 

The Motion of Diluent Molecules Associated with Side Chain Rotation... 

The other three polymers have additional rotation angles in the side chains, x and/or x. For poly(3-methyl-1-butene), the minimum was found in the three-dimensional plot. For poly(U-methyl-l-pentene) and poly(methyl methacrylate), the stable conformation of the side chain was first calculated with the fixed main chain conformation corresponding to the (7/2) and (5/1) helices, respectively. The potential energy was calculated against the main chain rotation angles, x and t2, by fixing x and x of the side chain at the values thus obtained. ... 

Figure 2. The dependence of the main-chain rotating-frame relaxation rate, and apparent diffusion coefficients of H2 and CO, on the concentration of TCP in PVC. The relaxation rates were measured at 3U kHz and 26 °C. The diffusion coefficients were measured at 270 cm-Hg and 27 °C.

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