Aplicacao de tecnicas dielecticas a estudos de dinamica e estrutura molecular misturas solidas polimero/corante, polimero/polimero e solucoes soluto polar/solventes liquidos apolares

Abstract

The experimental technique applied to the present study was the dielectric relaxation spectroscopy. Its basic concepts are presented in chapter 1 and a description in chapter 2. In chapter 3 we present the studies of the #alpha# relaxation of poly(vinyl acetate), PVAac, and of the dielectic relaxation of poly(vinyl acetate)/p-nitroaniline mixtures. It is shown that the p-nitroaline, pNA, acts like a normal plasticizer and its amino group interacts with the acetate groups of PVac via hydrogen bond interactions. In chapter 4 we study the effect of the same solute in the following dielectric relaxation processes: the poly(methyl methacrylate), PMMA, the the #beta# and #alpha# #beta# relaxations of the poly(ethyl methacrylate), PEMA, and the #alpha# #beta# relaxation of the poly(n-butyl methacrylate), PnBMA. We also present the study of the dielectric relaxation of the pure polymers. In PNMMA and PEMA the solute acts in a similar manner to a temperature increase. Consequently, the relaxation deviates to an #alpha# #beta# region accompained by a enhancement of the #alpha# relaxation and an inhibition of the #beta# process. In PnBMA/pNA mixturesd the #alpha# characteristics of the relaxation process of the matrix are enhanced. We conclude from the analysis of the different dielectric relaxations spectra, that the solute interacts with the PMMA via hydrogen bonding; this effect is less pronounced in PEMA and it is absent in PnBMA. In chapter 5 we present a preliminary suty of miscibility of poly(vinyl acetate)/poly(ethyl methacrylate) blends. We conclude that the 50 e 75% (Weight percent in PVac)blends are incompatible and that the 25% blend between 50 and 100 degrees C is compatible. Another purpose of this work was to apply the dielectric techniques to structural studies. In chapter 6 we accomplish this studying the conformational equilibrium of the trans-1,2-dibromocyclohexane in n-alkanes solvents: n-C_5, nC_6,n-C_8, nC_10 and n_C_1_2. Long n-dibromocyclohexane in n-alkanes solvents are characterized by a short range molecular order which stabilize the extended conformations. The aim of this work was therefore to check if the anisotropy of the molecular shape of the long n-alkanes could stabilize the diequatorial conformer of the trans-1,2-dibromocyclohexane (wich have a more elongate shape), knowing that the conformers have different dipole moments. The dipole moments mesured in each solvent have been compared with the dipole moment of the trans-1,2-dibromocyclohexane in cyclohexane, a globular solvent, and we observed that the dipole moment in the n-alkane solvents is higher than in the xcyclic solvent. There is also a slight of the dipole moment with the number of carbon atoms. This facts be interpreted as a stabilization effect of the fdiequatorial conformer with the increase of the degree of order of the solventAvailable from Fundacao para a Ciencia e a Tecnologia, Servico de Informacao e Documentacao, Av. D. Carlos I, 126, 1200 Lisboa / FCT - Fundação para o Ciência e a TecnologiaSIGLEPTPortuga