Dynamic mechanical and dielectric relaxations of poly(difluorobenzyl methacrylates)

Diaz-Calleja, R; Sanchis, MJ; Saiz, E; Martinez-Pina, F; Miranda, R.; Gargallo, L.; Radic D.; Riande, E

Abstract

This work reports the mechanical and dielectric relaxation spectra of three difluorinated phenyl isomers of poly(benzyl methacrylate), specifically, poly(2,4-difluorobenzyl methacrylate), poly(2,5-difluorobenzyl methacrylate) and poly(2,6-difluorobenzyl methacrylate). The strength of the dielectric glass-rubber relaxation of the 2,6 difluorinated phenyl isomer is, respectively, nearly three and two times larger than the strengths of the 2,5 and 2,4 isomers. The 2,4 isomer presents a mechanical ct peak the intensity of which is nearly two times that of the other two isomers. Both the mechanical and dielectric relaxation spectra display a subglass process, called gamma relaxation, centered in the vicinity of -50 degrees C at 1 Hz and, in some cases, a subglass beta absorption is detected at higher temperature partially masked by the glass-rubber relaxation. The mean-square dipole moments per repeating unit, [mu 2]/x, measured at 25 degrees C in benzene solutions, are 2.5 D-2, 1.9 D-2, and 5.0 D-2 for poly(2,4-difluorobenzyl methacrylate), poly(2,5-difluorobenzyl methacrylate) and poly(2,6-difluorobenzyl methacrylate), respectively. These results, in conjunction with Onsager type equations, permit to conclude that auto and cross-correlation contributions to the dipolar correlation coefficient may have the same time-dependence. On the other hand, dipole intermolecular interactions, rather than differences in the flexibility of the chains, seem to be responsible for the relatively high calorimetric glass-transition temperature of the 2,6 diphenyl isomer, which is, respectively, nearly 36 degrees C and 32 degrees C above the T-g's of the 2,4 and 2,5 isomers. Molecular Mechanics calculations give a good account of the differences observed in the polarity of the polymers. (C) 2000 John Wiley & Sons, Inc.

Más información

Título según WOS: Dynamic mechanical and dielectric relaxations of poly(difluorobenzyl methacrylates)
Título de la Revista: JOURNAL OF POLYMER SCIENCE PART B-POLYMER PHYSICS
Volumen: 38
Número: 16
Editorial: John Wiley & Sons Inc.
Fecha de publicación: 2000
Página de inicio: 2179
Página final: 2188
Idioma: English
URL: http://doi.wiley.com/10.1002/1099-0488%2820000815%2938%3A16%3C2179%3A%3AAID-POLB110%3E3.0.CO%3B2-I
DOI:

10.1002/1099-0488(20000815)38:16<2179::AID-POLB110>3.0.CO;2-I

Notas: ISI