It is shown that isotropic (or average) nuclear resonance shifts for a nucleus in a paramagnetic molecule in solution, and in a polycrystalline solid, can be used to distinguish between Fermi contact and "pseudocontact" contributions to isotropic nuclear-hyperfine interactions. The pseudocontact interaction is that isotropic hyperfine coupling which arises from the combined effects of (electron-spin)-(nuclear-spin) coupling, (electron-orbit)-(nuclear-spin) coupling, and electron spin-orbit interaction. When the magnetic hyperfine interaction between the electronic moment and nuclea.r spin is approximated by a point dipolar interaction, and the isotropic hyperfine interaction is exclusively pseudocontact, then the isotropic nuclear shift in a polycrystalline solid exceeds the solution shift by the factor 3(gll +U)!(gll +2U) where gil and u are the spectroscopic splitting factors parallel and perpendicular to the molecular symmetry axis. Isotropic shifts due to the Fermi contact interaction are the same for both solid state and solution cases.

We present a theory for how a shear stress alone can induce structural changes in a glassy polymer to break up the rigidity of the glass and allow flow. We consider a molecular model in which the shear-stress field is introduced as a bias on the rotational conformation of backbone bonds. It is argued that the fraction of flexed bonds is transiently increased from that in the glass and that this, additionally causing a volume increase, produces a polymer structure resembling the liquid at some temperature above the glass transition. Using these considerations along with several well-known empirical relations, we have calculated the plastic properties of polystyrene and polymethyl methacrylate. These calculated properties correspond reasonable well with the cold-drawing data available.

NotesYol. 61 the OH groups in hydrated ketones are perfectly normal alcohols.The strong absorption doublet in the 1100 cm.-1 region due the C-0 stretch shows much greater splitting for triquinoyl than for the other hydrates. This may be due to the presence of two kinds of OH groups (polar and equatorial).In conclusion, the infrared spectra of leuconic acid and triquinoyl definitely indicate that all the carbonyls are completely hydrated, for both compounds. This is indicated not only by the absence of the characteristic strong C=0 absorption in the region from 1500 to 1800 cm.-1, but also by the agreement between the spectra of these molecules with that of the known hydrate, chloral hydrate.The spectra of all three molecules are entirely consistent with the characteristic frequencies expected for normal OH groups.It is a pleasure to acknowledge the many helpful discussions with Dr. Norman C. Baenziger.

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SYNOPSISThe melting behavior of poly (butylene terephthalate) (PBT) has been investigated, and a simulation has been performed to determine whether the multiple melting endotherms observed during the thermal analysis of PBT can be explained by the simultaneous melting and recrystallization of an initial distribution of crystal melting temperatures that contains only one maximum and two inflection points. Specimens that were cooled at constant rates from the melt showed between one and three melting endotherms upon heating in a differential scanning calorimeter (DSC) . The position and breadth of the crystallization exotherms upon cooling from the melt and small-angle x-ray scattering showed that as the cooling rate is increased, the distribution of melting temperatures broadens and shifts to lower temperatures. By combining temperature-dependent recrystallization with an initial distribution of melting temperatures, simulated DSC curves were produced that agreed well with experimental DSC curves. In instances of triple peaked curves, the high temperature peak was due to crystals formed during the scanning process, and the middle and low temperature peaks were due to crystals originally present in the material. Satisfactory agreement between the experimental and simulated curves was found without considering additional crystallization from the amorphous regions during the scanning process.Keywords: poly (butylene terephthalate) , multiple melting endotherms from differential scanning calorimetry (DSC) of poly (butylene terephthalate) thermal behavior of poly (butylene terephthalate)