Michael F. Froix

NMR relaxation‐time studies of poly(N‐vinyl carbazole) and sorbed‐O2 effects

Proton spin‐spin (T2) and spin‐lattice (T1) relaxation times have been measured in order to elucidate the molecular dynamics in poly(N‐vinylcarbazole) (PVK). Measurements were obtained on samples covering a broad range of molecular weights in air, O2, N2, and in vacuo. Correlation frequencies νc determined from NMR data were used in conjunction with dielectric data to construct transition maps. The α,β relaxations associated with main‐chain and segmental motion exhibit temperature‐dependent behavior very similar to that observed in polystyrene (PS). The γ relaxation in PVK is highly unusual in that it is dielectrically active and manifested in the T2 data only in the presence of O2. A detailed interpretation of this effect is provided, leading to the conclusion that O2 diffusion is severely restricted at low temperatures and that torsional oscillation of the carbazole group is responsible for the γ relaxation. It is proposed that the presence of O2 leads to relaxation by slow spin diffusion to the paramag...

The Effect of Cooling Rate and Magnetic Field on the NMR Relaxation and Thermal Behavior of [N- (p-methoxybenzylidene) -p-n- butylaniline] (MBBA)

Abstract NMR relaxation time measurements and the dsc thermal behavior of the solid state of MBBA have been examined as a function of cooling rate and aligning magnetic field. The results indicate a complicated solid state morphology as a result of these effects. Aside from the normal crystal structure, anisotropies are introduced by the aligned magnetic field and the liquidcrystalline structure that is retained on quenching to the amorphous metastable state. These anisotropies are reflected in the occurance of additional endotherms in the thermal data, and by separate relaxations for methyl reorientation in the normal crystal and the metastable amorphous material in the nmr data. The activation energies for methyl reorientation are determined.

The Effect of Rapid Cooling and a Magnetic Field on the NMR Relaxations and Thermal Behavior of [N-(P-ethoxybenzylidene)-p-butylaniline] (EBBA)

Abstract Rapid cooling of EBBA from the nematic phase results in a mixture of amorphous and crystalline material. The presence of these two phases are detected in the nmr relaxation data by the occurrence of two separate relaxations for reorientation of the methyl/ethyl groups in each of these phases. Aligning of the molecules in the liquid crystalline state by a magnetic field prior to crystallization gives rise to morphological changes which are manifested by a melt temperature some two degrees higher than the normal crystal melt.

Effect of molecular oxygen on the n.m.r. relaxation times of some aromatic polymers

Abstract Proton spin-lattice (T1) and spin-spin (T2) relaxation times are reported for poly(2-vinylpyridine), poly(1-vinylanthracene) and polycarbonate in air, oxygen and in vacuo. The results substantiate earlier findings that oxygen complexes with the aromatic rings giving rise to T1 minima which are not intrinsic to the polymers. This effect appears to be fairly general for aromatic containing polymers. For those polymers containing low temperature relaxations intrinsic to the polymer, the oxygen paramagnetic effect can complicate the relaxation behaviour and, in some cases, totally mask the intrinsic processes. The transitions in T1 and T2, due to the torsional oscillation of the anthracene side group in poly(1-vinylanthracene), is much better defined than the corresponding transitions for previously reported aromatic vinyl polymers. The activation energy for the motion of the side group is comparable to that of polystyrene and poly(N-vinylcarbazole).

A dynamic characterization via relaxation techniques of the shell membranes of the domesticated fowl (gallus/gallus (L.))

Abstract The shell membrane is made up of a unique three-layered structure which consists of outer, inner and limiting membranes. The structure is capable of adsorbing water in excess of 2.5 times its weight. The water containing species give rise to dielectric and n.m.r. relaxations associated with tightly bound and loosely bound water. An additional relaxation which appears to be intrinsic to the biomolecule is observed at low temperatures. The intensity and effectiveness of this relaxation is governed by the amount of water present. The facility of the membrane to interact with water enables the molecular reorientational process of the membrane itself to take place with a greater ease, with the result that the structure changes its deformation characteristics from that of a brittle to a low modulus elastomeric material. Thermal treatment of the membrane alters its relaxation properties. The membranes ability to adsorb water is drastically reduced and the molecular reorientational processes do not occur as readily. As a result, the change from brittle fracture to low modulus yield that is observed for a saturated, non-heat treated material is not found, and the water-saturated, heat treated material fails in a brittle manner. It appears that the irreversible changes that take place on heat treatment do so gradually above room temperature reaching an appreciable rate above 410K. No changes corresponding to those found in the relaxation, differential scanning calorimetry (d.s.c.) and mechanical measurements are observed in the scanning electron microscopy (s.e.m.) data of the heat treated material.

Nuclear spin relaxation and molecular motions in sebacate polyesters

Abstract In this study, pulsed NMR techniques were used to probe the molecular motions occurring in poly(hexamethylenesebacate) (HMS), and its amorphous isomer poly(2-methyl-2-ethyl-1,3-propylenesebacate (MEPS), and in particular, to examine the perturbations in the molecular motions of HMS and MEPS that arise as a result of block copolymerization. The results show a low-temperature β-relaxation due to local motion of the methylenes of the chain backbone, an α-relaxation associated with the glass transition, and an αc-relaxation due to the melting of the crystalline phase. Both α-and β-relaxations in the block copolymer are only slightly perturbed, and this suggests that the blocks are incompatible. The β-relaxation of HMS is confined to the amorphous regions of the polymer. Although sample preparation had little effect on the degree of crystallinity, large differences in the relaxation behavior were observed when the sample preparation was varied.