Poly modeling phase shifts

Fig. 20. The calculated phonon dispersion curves for Na-poly(dA) poly(dT) in the directions as indicated (mode wave-number V vs. phase shift 0). The solid curves are the plus modes and the dashed curves are the minus modes. The model considers eight nucleotide pairs per unit cell and the poly(dA) poly(dT) to be essentially a one dimensional helical crystal with a helix axis taken as ( and the two coordinates at right angles taken as tj and f [87P3],...

EOS models were derived for polymer blends that gave the first evidence of the severe pressure - dependence of the phase behaviour of such blends [41,42], First, experimental data under pressure were presented for the mixture of poly(ethyl acetate) and polyfvinylidene fluoride) [9], and later for in several other systems [27,43,44,45], However, the direction of the shift in cloud-point temperature with pressure proved to be system-dependent. In addition, the phase behaviour of mixtures containing random copolymers strongly depends on the exact chemical composition of both copolymers. In the production of reactor blends or copolymers a small variation of the reactor feed or process variables, such as temperature and pressure, may lead to demixing of the copolymer solution (or the blend) in the reactor. Fig. 9.7-1 shows some data collected in a laser-light-scattering autoclave on the blend PMMA/SAN [46],... 

In phosphazene chemistry, preparation and reactions of small molecule, linear phosphazenes continue to attract interest. This year numerous papers have explored the utility of the aza-Wittig reaction in the synthesis of complex molecules with particular reference to nitrogen heterocycles. In cyclophosphazene chemistry, the shift of emphasis to materials which are monomers themselves or models for phosphazene polymers is apparent. The synthesis and characterization of poly(phosphazenes) is an active area with extensive interest in phosphazene based polyelectrolytes being noted. Solid state NMR has been shown to be a valuable tool for the study of both structure and phase changes in poly(phosphazenes). 

Another recent reporP uses a set of chemically robust aryl fluorides as molecular tags. These molecules exhibit chemical shifts that range from -55 to -25 ppm relative to fluorobenzene, and are tolerant to a wide variety of chemical transformations in solid-phase chemistry. Poly-A-alkylglycines were chosen as a model system for the preparation of combinatorial... 

An interesting phase behavior was observed experimentally [38] for the system poly(ethylene-co-methyl acrylate) in the solvent ethylene (Figure 10.13). Starting from low-density polyethylene, an increasing content of methyl acrylate in the copolymer shifts the demixing curve to lower pressures up to 13 mol% of methyl acrylate in the copolymer, whereas with further addition of methyl acrylate the solubility again decreases. In this case, the binary parameter is a linear function of the copolymer composition [38]. Figure 10.13 demonstrates the performance of the PC-SAFT EOS. The model is able to describe the observed dependence on temperature and molar mass as well as the nonmonotonic dependence on copolymer composition. 

---