Search results for "transition"

NLO-polymers containingtert-butyloxycarbonyl protecting groups: Modification after processing leading to thermally stable nonlinear optical materials

1997

Infrared spectroscopic study of a phenyl benzoate side group—methacrylate main chain polymeric liquid crystal

1994

Abstract The temperature dependence of the infrared dichroism of a side chain polymeric liquid crystal was investigated for two homogeneously oriented samples, one aligned with a PVA coating and the other aligned by a magnetic field. From the apparent order parameters, it was found that the rotation of the mesogenic side group was restricted. Not only the rigid part of the side group, but also the alkyl chains were found to be partly ordered. Realignment of the side groups was observed in the case of the magnetically aligned sample at the smectic-nematic transition temperature. Unlike the other absorption bands, the C˭O bond vibration band shifted to higher wavenumbers with increasing tempe…

Influence of the modification, induced by zirconia nanoparticles, on the structure and properties of polycarbonate

2013

Melt compounding was used to prepare polycarbonate (PC)–zirconia nanocomposites with different amounts of zirconia. The effect of the zirconia loading, in the range of 1–5 wt.%, on the structure, mechanical properties and thermal degradation kinetics was investigated. The zirconia nanoparticle aggregates were well dispersed in the PC matrix and induced the appearance of a local lamellar order in the polycarbonate as inferred by SAXS findings. This order could be a consequence of the intermolecular interactions between zirconia and the polymer, in particular with the quaternary carbon bonded to the methyl groups and the methyl carbon as inferred from the NMR results. The presence of zirconia…

Methylcellulose-Based Edible Films and Coatings:  2. Mechanical and Thermal Properties as a Function of Plasticizer Content

1997

Several edible films based on methylcellulose and polyethylene glycol 400 (PEG400) were prepared and stored until equilibration at different relative humidities. Tensile stress−strain curves show very different behaviors as a function of PEG400 and relative humidity. Tensile strength strongly depends on relative humidity and then on water content, more than on PEG400 content. On the contrary, elongation is dependent both on water and PEG400. These differences correspond to the glass transition of the polymer, which affects the elongation more than the tensile strength. However, from DSC measurements, it appears that the PEG400 has no or a very low compatibility with the methylcellulose matr…

Neutron reflectometry studies on the interfacial width between polystyrene and various poly(alkylmethacrylates)

1999

From neutron reflectometry we have obtained the interfacial width (typically 2-8 nm) between incompatible polymers above the glass transition temperatures. The investigated polymer bilayers consist of a deuterated polystyrene top layer and various poly(alkylmethacrylates) as a bottom layer. We obtained interesting effects of the length of the alkyl group on the interfacial width. Using mean-field theory we calculate Flory-Huggins-Stavermann interaction parameters X from the interfacial width a I data. These results are compared with investigations of the interfacial width between deuterated poly(methylmethacrylate) and respective polyalkyl-methacrylates.

Rheological characterization of polycaprolactam anionically synthesized in the presence of lithium chloride

1980

Melt viscosity and dynamic-mechanical data are reported for samples obtained by anionic polymerization of caprolactam, in the presence of LiCl. The full body of results is essentially in line with those previously reported relative to mixtures of inorganic salts and commercial nylon 6, In particular a drastic-decrease of the melting point and of the rate of crystallization is confirmed as well as an increase of the glass transition temperature and of the melt viscosity. Some quantitative differences exist, which may be attributed to the different molecular weight distribution in the polymers employed in the present work.

Diffusion of spherical micronetworks in polymer diluent systems and melts studied by dynamic light scattering techniques

1994

Spherical polystyrene (PS) micronetworks can be prepared in microemulsion with bulk radii of 5–60 nm and different cross-linking densities. The diffusion of these PS spheres has been studied in polymer diluent systems ranging from dilute solutions to plasticized melts by using forced Rayleigh scattering and photon correlation spectroscopy. On increasing the PS concentration, a colloid glass transition is observed at a volume fraction ΦC ≈ 0.64 of the swollen spheres. At higher concentration inside the “colloid glass” state the sphere diffusion is slowed down and becomes very complex but can be observed up to the limit of a melt of collapsed spheres.

Effect of cooling rate on the viscoelastic properties in the plastic zone of solid polymers

1979

PMMA and PC samples were subjected to several cooling rates from the glass transition temperature.

Extension of the Concept of Intrinsic Viscosities to Arbitrary Polymer Concentration: From [η] via {η} to Intrinsic Bulkiness

2019

The capabilities of an alternative definition of intrinsic viscosities [η] published some years ago is being studied by means of comprehensive viscometric data reported in the early days of polymer science. It introduces the generalized intrinsic viscosity {η} as the specific hydrodynamic volume at arbitrary polymer concentration c. {η} quantifies the size of the flow unit and decreases monotonously for T ≫ Tg (glass transition temperature) as a function of c but passes a pronounced minimum as T approaches Tg. In the limit of the pure polymer melt, {η} becomes ; this newly introduced property is termed intrinsic bulkiness, by analogy to the intrinsic viscosity, and provides noncalorimetric …

The glass transition behaviour of salted nylon 6

1981

Glass transition measurements of nylon-6/lithium halides mixtures have been carried out in wide range of frequency with the aid of different experimental techniques. The results show an increase of the glass transition temperature when the salt is present and prove the larger effectiveness of lithium chloride with respect of lithium bromide. This effect, in line with the large reduction of the specific volume caused by the salt, is due to the formation of a pseudo-cross-linking between lithium ions and the carbonyl-oxygen groups of the polyamide.