Browsing by Author "RIANDE, E"

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    RELAXATION BEHAVIOR OF SEMIRIGID CHAINS IN THE AMORPHOUS STATE
    (1994) CALLEJA, RD; SAIZ, E; RIANDE, E; GARGALLO, L; RADIC, D
    Dielectric and mechanical behaviour of two polymers having severe restrictions on the conformational versatility of the backbone, namely poly(monocyclohexylmethylene itaconate) (PMCMI) and poly(dicyclohexylmethylene itaconate) (PDCMI), have been studied. Both polymers present a weak glass-rubber relaxation named alpha and two stronger absorptions in the glassy state that, in increasing temperature order, are called beta- and gamma- relaxations. Both mechanical and dielectric beta-peaks are located in the same region of the spectra and have the same activation energy, which suggest that both relaxations are caused by the same molecular mechanisms. The analysis of the dipole moments of both polymers suggest that they behave as freely joint chains as far as their polarity is concerned. The dipolar correlation coefficients in the sub-glass region were calculated by assuming that the dielectric activity is only produced by reorientations of the side groups with respect to the frozen main chains. The fact that the values of the coefficients thus calculated are somewhat larger than the experimental values suggests that dipolar intermolecular interactions cannot be neglected in the analysis of the dielectric behaviour of these polymers.
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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.