Poly force constants

We found it unrealistic to try to fit the longitudinal acoustic velocity to short range forces for A conformation polydG.poly dC. A value of 8 = 2.64 gave a velocity Vj = 1094 m/s. This value of 8 would imply the average near neighbor nonbonded force constant is = 1.0 md/A. Fitting the observed value (1) of 2600... 

The actual values of force constants are determined by a poly-... 

Energy parameters and charge-transfer spectra of complexes of Br2 with several substituted pyridines have now been compared with the force constants k(Br—Br) and k(N- Br2) and with the properties of the donors. The complexes with orr/to-substituted pyridines show systematic deviations from the relations found to be valid for the other donors. The n.m.r. spectrum of the pyridine-Br2 complex in a nematic phase has been obtained and analysed. The results indicate that the donor-acceptor interaction is similar to that found in the solid state for other halogen-pyridine complexes. The equilibrium constant for the formation of the 1 1 complex of Br2 with hexamethyl-phosphortriamide (HMPA) has been determined by n.m.r. spectroscopy. Solid adducts of Br2 with poly-HMPA could also be prepared. 

The kco force constants for a range of Group 6 poly(pyrazolyl)borate c/s-dicarbonyl complexes Tp M(L )(CO)2 with three-valence electron ligands (L ) that are isoelectronic with CR are tabulated in Table VI and exhibit the previously... 

Brillouin spectroscopy can also be used to study the change of sound velocity with deformation. Anders et al. reported the longitudinal sound velocity in stretched poly (urethane) and poly (diethylsiloxane) (PDFS, Figure 60.8) networks [15]. They used the lattice-model to determine the force constants [11]. The samples showed different deformation-dependent behavior of the force constants. For the... 

The refinement of an empirical force field for a macromolecule usually starts with the vibrational analysis of a smaller model system of known structure followed by a transfer of these force constants to the larger system, with possible subsequent force constant adjustments. In the case of the polypeptides, the preferred model system for the peptide group has been fra 5-N-methylacetamide (NMA), CH3CONHCH3. Synthetic polypeptides of known structure such as )9-sheet polyglycine (PG ), R = H, and a-helical and )8-sheet poly(L-alanine) (PLA), R = CH3, have served as basic examples of the polypeptide systems. 

Figure 26.33 shows the side force coefficient as function of log speed for different temperatures at a constant load and slip angle for a tire tread compound based on 3,4 cw-poly-isoprene, a polymer... 

We have examined the correlation of binding constants for 4-substltuted phenols with five abiotic polymers using an equation based on Inteinnoleoular forces and sterlc effects which will be described later in the section on transport parameters. In the case of poly(ethylene glycol) a borderline dependence on Vg was observed (12). The substituent was considered to have the form ZW where Z is the atom bonded to the ring. 

The basic pattern of the coagulation of polymer latices with aluminum salts has been clearly demonstrated by the work of Matijevic and his collaborators (1968) using styrene-butadiene. poly(vinyl chloride) (1977). and PTFE (1976) latices. The results obtained by Matijevic and Force (1968b) for the coagulation of styrene-butadiene latices using alumi num nitrate are shown in Fig. 13. From these it can be seen that up to a pH of 3.4 the ccc remains constant at 5 x 10 mol dm" and then decreases between pH 3.4 and 4.8 to reach a constant value of... 

The most common type of stress-strain tests is that in which the response (strain) of a sample subjected to a force that increases with time, at constant rate, is measured. The shape of the stress-strain curves is used to define ductile and brittle behavior. Since the mechanical properties of polymers depend on both temperature and observation time, the shape of the stress-strain curves changes with the strain rate and temperature. Figure 14.1 illustrates different types of stress-strain curves. The curves for hard and brittle polymers (Fig. 14.1a) show that the stress increases more or less linearly with the strain. This behavior is characteristic of amorphous poly-... 

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