Syntheses and characterizations of new copolymers of vinylidene cyanide with para substituted α acetoxystyrenes

Summary Vinylidene cyanide has been copolymerized in solution by radical reaction with equal initial mole fraction of para substituted acetoxystyrenes. The copolymers have been characterized by means of DSC, TGA and GPC. These products are stable up to 220° and have no visible glass transition temperature. The microstructure of these new copolymers has been studied by ¹³CNMR; they have an alternating structure and monomers units are arranged in head-to-tail placements.     

Etude cristallochimique et dielectrique des phases du systeme quaternaire LiNbO3−LiTaO3−NaNbO3−NaTaO3

A crystal chemical study of the quaternary system LiNbO₃ ? LiTaO₃ ? NaNbO₃ ? NaTaO₃ has been carried out. The obtained phase diagram depends on the temperature. At 1370 K for instance three solid solutions appear, they are related to perovskite, LaCoO₃ and LiNbO₃ - type structure. Most of these materials have ferroelectric - paraelectric transitions. The Curie temperature increases by substitution of sodium by lithium and tantalum by niobium. They have potential applications in piezoelectricity, pyroelectricity and electrooptics.     

Strain based triangular finite element for plate bending analysis

ABSTRACT

In this work, the formulation of a new triangular finite element is presented for static and free vibration of plate bending. The developed element which contains the three essential external degrees of freedom at each of the three corner nodes is based on the Reissner/Mindlin theory and the strain-based approach. This element is based on the linear variation of the three bending strains and constant transverse shear strains. The present element performances are evaluated through several tests related to moderated thick and thin plates with various shapes where it is found to be numerically more efficient than the bilinear element.     

Etude cristallochimique,dielectrique et pyroelectrique de la solution solide Na1−xLix(Nb0,6Ta0,4)O3 (0,02 ⩽ x ⩽ 0,20)

A solid solution with formulation Na_1?xLi_x(Nb_0.6Ta_0.4)O₃ (0.02 ? x ? 0.20) and a perovskite related structure has been prepared by substituting sodium by lithium in Na(Nb_0.6Ta_0.4)O₃. The ferroelectric Curie temperature increases with x from 308 to 428 K. The pyroelectric properties have been investigated. The high performances may lead to appropriate applications.     

Etude optique et couplage ferroélectrique-ferroélastique de cristaux de composition Li0, 02Na0, 98NbO3

Crystal of composition Li_0.02Na_0.98NbO₃ is ferroelectric at room temperature (space group Pc2m, T_c = 640 K). Two kinds of domain walls parallel to (101) or (141) planes have been observed at 300 K. The birefringence n_a-n_c and the domain pattern have been investigated from 300 to 950 K. Four transitions have been detected at T₂ = 540 K, T₃ = T_c = 640 K, T₄ = 825 K and T₅ = T′_c = 940 K. The transition at T′_c is of ferroelastic-prototype type. The switching of the polarization associated with the disappearing of the domain walls is in good agreement with a ferroelectric-ferroelastic coupling.     

Kinetic modeling of an unsaturated polyester resin using two complementary techniques: Near infrared spectroscopy and heat flux sensors

This article concerns the characterization of the polymerization kinetics of an unsaturated polyester resin containing a large excess of styrene. For this type of resin, DSC measurements happen to not be satisfactory. Two complementary techniques were then used: an in situ near infrared spectroscopy and a PVT mold equipped with heat flux sensors. This article describes these two experimental devices and the methods used to obtain the experimental data. By monitoring the evolutions of unsaturated polyester and styrene conversions with near infrared spectroscopy, it was possible to identify two different chemical mechanisms occurring during the resin cure responsible for the measured two‐peaks thermograms. Their relative importance was quantified. A kinetic model representative of these two coupled reactions was established and its parameters evaluated from the thermal analysis. This model was able to predict the kinetic behavior of the resin outside of the domain of study, even at high temperature, where the second peak of the thermogram vanishes while the final conversion decreases. This model was also able to simulate the resin cure during experiments with an imposed heating rate. POLYM. ENG. SCI. 45:846–856, 2005. © 2005 Society of Plastics Engineers