Browsing by Author "DIAZCALLEJA, R"

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    CALORIMETRIC STUDY OF SOME POLY(MONO-NORMAL-ALKYL ITACONATES)
    (1991) DIAZCALLEJA, R; RIBESGREUS, A; GARGALLO, L; RADIC, D
    A calorimetric study of poly(mono-n-alkyl itaconates) containing 8, 10, 12 and 14 carbon atoms in the side chain was performed. No glass transition temperature (T(g)) was observed in the temperature range 213-263 K, but a melting process was observed for the dodecyl and tetradecyl derivatives, which was attributed to crystalline order in the long side chains.
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    DIELECTRIC AND VISCOELASTIC RELAXATIONS IN POLY(DICYCLOHEXYL ITACONATE)
    (1992) DIAZCALLEJA, R; GARGALLO, L; RADIC, D
    The relaxation spectrum of poly(dicyclohexyl itaconate) (PDCHI) was studied by dynamic mechanical, DC dielectric and thermally stimulated current measurements. Four relaxations, alpha, beta, gamma and delta, were obtained. The only method by which all four peaks were observed is that of dynamic dielectric measurements because of the broad range of frequencies employed. The beta, gamma and delta-relaxations were characterized by the activation energy in a relaxation map. A tentative explanation of the molecular origin of each absorption is proposed. In the case of thc alpha-relaxation we have used two transformations, one from the permittivity to polarizability and thc second from compliance to deformability in order to make evident the existence of this relaxation.
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    DIELECTRIC RELAXATIONS IN POLY(MONOCYCLOHEXYL ITACONATE)
    (JOHN WILEY & SONS INC, 1992) DIAZCALLEJA, R; GARGALLO, L; RADIC, D
    A study of the dielectric relaxation spectrum of poly (monocyclohexyl itaconate) (PMCHI) is performed by means of two experimental techniques: first, at variable frequency in the audio zone and, second, by thermally stimulated depolarization currents. Because of the high conductivity of the samples, there is a hidden dielectric relaxation that can be detected by using the macroscopic dynamic polarizability alpha* defined in terms of the dielectric complex permittivity epsilon* by means of the equation-alpha* = (epsilon* - 1)/(epsilon* + 2). The transformation performed through this equation is discussed in order to obtain the dielectric relaxations in the zone of high temperatures and low frequencies of the spectrum.
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    DIELECTRIC RELAXATIONS IN POLY[2,2-PROPANE-BIS-(4-PHENYL THIOCARBONATE)]
    (1992) MARTINEZ, ES; DIAZCALLEJA, R; RIBAS, SM; GARGALLO, L; RADIC, D
    The dielectric relaxation properties of poly[2,2-propane-bis-(4-phenyl thiocarbonate)] (PTC) have been studied. The existence of crystallinity, which can be eliminated by quenching, is detected. The degree of crystallinity of polymer samples was determined by differential scanning calorimetry in order to investigate the effect of this factor on the dielectric behaviour of this polymer. The thermal degradation of the samples was studied by thermogravimetry. The degradation of the polymer begins before the glass transition temperature T(g). The dielectric spectrum is complex showing several relaxation phenomena. With increasing temperature a gamma-relaxation can be observed at - 100-degrees-C (5 kHz). The activation energy obtained from an Arrhenius plot (ln f vs T-1) is 6 kcal mol-1. At 160-degrees-C the alpha-relaxation which is associated with the glass transition temperature T(g) is detected. The dielectric behaviour of this poly(thiocarbonate) is compared with the corresponding poly(carbonate).
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    DIELECTRIC-RELAXATION BEHAVIOR OF POLY(CYCLOHEXYLMETHYL METHACRYLATE) AND POLY(BENZYL METHACRYLATE)
    (1989) RIBESGREUS, A; DIAZCALLEJA, R; GARGALLO, L; RADIC, D
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    DIELECTRIC-RELAXATION BEHAVIOR OF POLY(MONO-N-ALKYL ITACONATES)
    (1991) RIBESGREUS, A; DIAZCALLEJA, R; GARGALLO, L; RADIC, D
    Dielectric relaxation measurements on a family of poly(mono-n-alkyl itaconates) have been performed. Two relaxation peaks have been observed within the temperature range studied. The first one at lower temperature (153 K at 1 kHz), which we call the gamma-peak and have attributed to motion in the lateral chains involving methylene sequences, depends on the length of the side-chain. The second relaxation labelled-beta (233 K at 1 kHz) is related mainly to motion of the lateral group. A peculiar behaviour has been observed in the case of poly(mono-tetradecyl itaconate). The results have been discussed in terms of the different possible motions of the side-chains.
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    DIELECTRIC-RELAXATION IN POLY(MONOBENZYL ITACONATE)
    (1991) DIAZCALLEJA, R; RIBESGREUS, A; GARGALLO, L; RADIC, D
    The dielectric relaxation properties of poly(monobenzyl itaconate) have been studied and four relaxation processes (alpha, beta, gamma and delta) have been found. These processes respectively appear in the decreasing order of temperatures 100, 20, -42 and - 110-degrees-C at 2 kHz. The best defined relaxations, alpha and gamma have been described in terms of semiempirical models. Different molecular origins for each relaxation have been proposed by comparison with other polymers of similar structures, particularly with poly(benzyl methacrylate). In the general case, the higher complexity of the side chains in poly(methacrylates) as well as in poly(itaconates) involves the possibility of multiple relaxation mechanisms that are not always easy to interpret.
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    DYNAMIC MECHANICAL-PROPERTIES OF POLY(MONOCYCLOHEXYL ITACONATE)
    (ELSEVIER SCI LTD, 1992) DIAZCALLEJA, R; GARGALLO, L; RADIC, D
    Accurate dynamic mechanical measurements were performed on poly(monocyclohexyl itaconate) at different frequencies over a wide temperature range. Three main relaxations could be observed at different temperatures, which were labelled as gamma, beta and alpha-relaxations. The gamma-relaxation was attributed to the motions of the cyclohexyl group, specifically to the chair-chair flipping of the ring; and the beta-relaxation to the rotation of the side carboxylic groups. In order to analyse alpha-relaxation a mechanical model was used which considered an isotropic continuum containing spherical isotropic non-interacting particles. Qualitative validity of this hypothesis was found and the results were consistent with the dielectric data obtained for the same polymer.
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    RELAXATION BEHAVIOR, INTRAMOLECULAR INTERACTIONS, AND LOCAL MOTIONS ON MONOSUBSTITUTED ESTERS OF POLY(ITACONIC ACID)
    (1994) DIAZCALLEJA, R; SAIZ, E; RIANDE, E; GARGALLO, L; RADIC, D
    The mechanical relaxation spectrum of poly(monocyclohexylmethylene itaconate) (PMCMI) exhibits two well-developed absorptions in the glassy state that in increasing temperature order are named gamma and beta absorptions. Owing to the restricted conformational versatility of the backbone, the polymer presents a weak glass-rubber relaxation whose intensity is significantly lower than that of the gamma absorption. Comparison of the mechanical spectrum of this polymer with that of poly(dicyclohexylmethylene itaconate) (PDCMI) allows the conclusion that the beta relaxation is produced by motions in which the - COOCH2C6H11 side groups are involved. The location of the mechanical gamma gamma peak suggests that this absorption is produced by flipping conformational transitions in the cyclohexyl residue. Three dielectric absorptions are observed in the glassy state of PMCMI which in increasing temperature order are called delta, gamma, and beta relaxations. Both the location and the activation energy of the dielectric and mechanical beta absorptions suggest that both relaxations are caused by the same molecular motions. Dipolar interactions in the liquid and glassy state are calculated and the results compared with those experimentally evaluated. (C) 1994 John Wiley & Sons, Inc.
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    RELAXATION PROPERTIES OF MOLECULAR CHAINS WITH RESTRICTED CONFORMATIONAL VERSATILITY OF THE BACKBONE
    (AMER CHEMICAL SOC, 1993) DIAZCALLEJA, R; SAIZ, E; RIANDE, E; GARGALLO, L; RADIC, D
    This work deals with the study of the dielectric and mechanical behavior of polymers in which the conformational versatility of the backbone is severely restricted. The mechanical spectrum of the model, poly(dicyclohexylmethylene itaconate) (PDCMI), presents two absorptions in the glassy state that in increasing temperature order are called gamma and beta relaxations. Contrary to what occurs in most amorphous systems, the polymer only presents a weak glass-rubber relaxation, named alpha. By using deconvolution techniques to separate the peaks associated with the different absorptions, one finds that the strength of the beta peak is nearly 6 and 3 times larger than the strength of the alpha and gamma relaxations, respectively. The dielectric spectrum also presents two well-developed absorptions in the glassy state, one called gamma, in the lower temperature side of the spectrum, that is much weaker than the beta, located close to the glass-rubber relaxation; in addition, a shoulder at low frequencies in the spectrum is detected that presumably corresponds to a peak (beta') that overlaps with the beta process. Although conductivity processes overlapping with the dipolar contribution to the alpha absorption preclude the possibility of determining the strength of this latter relaxation, the analysis of the electric loss spectra permits us to conclude that both the dipolar alpha and beta relaxations roughly have the same intensity. The values of the relaxation strength for the beta and gamma relaxations at 100 Hz are 0.88 and 0.07, respectively. The fact that both the mechanical and dielectric beta relaxations are located in the same region of the spectrum, and also have the same activation energy (almost-equal-to 42 kcal mol-1), indicates that both relaxations are caused by the same molecular mechanisms. Thermally stimulated discharge current (TSDC) spectra exhibit a well-developed glass-rubber relaxation whose peak is centered at 50-degrees-C, followed by two subglass relaxations, beta and gamma. The activation enthalpy for the peaks obtained by partial depolarization techniques in the beta region is nearly half of that corresponding to the same zone of the spectrum obtained in a variable electric field. The analysis of the dipole moments of the chains suggests that as far as their polarity is concerned they behave as freely jointed chains. The dipolar correlation coefficient for the subglass region is calculated by assuming that the dielectric activity is only produced by reorientations of the side groups with respect to the frozen main chain. The fact that the value of the coefficient thus obtained is somewhat larger than the experimental one suggests that dipolar intermolecular interactions cannot be neglected in the dielectric behavior of these chains.