INTEMA   05428
INSTITUTO DE INVESTIGACIONES EN CIENCIA Y TECNOLOGIA DE MATERIALES
Unidad Ejecutora - UE
artículos
Título:
Nanostructured epoxies based on the self-assembly of block copolymers: a new miscible block that can be tailored to different epoxy formulations
Autor/es:
S. MAIEZ-TRIBUT; J. P. PASCAULT; E. R. SOULÉ; J. BORRAJO; R. J. J. WILLIAMS
Revista:
MACROMOLECULES
Editorial:
American Chemical Society
Referencias:
Lugar: Washington DC; Año: 2007 vol. 40 p. 1268 - 1273
ISSN:
0024-9297
Resumen:
Nanostructured thermosets may be obtained by the self-assembly of
amphiphilic block copolymers (BCP) in a reactive solvent and fixation of the
resulting morphologies by the cross-linking reaction. Nanostructuration requires
the presence of a bock that remains miscible in the thermosetting polymer
during polymerization. The selection of the miscible block depends on the
particular system and in some cases (e.g., for epoxy-amine network based on diglycidyl ether of bisphenol A, DGEBA, and
4,4-diaminodiphenylsulfone, DDS) it is very difficult
to find such a block. In this manuscript it is shown that random copolymers of methyl
methacrylate (MMA) and N,N-dimethylacrylamide (DMA) containing
different molar fractions of DMA, can be used as a universal miscible block
for the nanostructuration of epoxies, a fact that is particularly illustrated
for a DGEBA-DDS epoxy network. The miscibility of the random copolymer during
formation of the epoxy network was first analyzed determining cloud-point
conversions as a function of the molar fraction of DMA in the copolymer. A thermodynamic model of the phase separation was performed using
the Flory-Huggins model and taking the polydispersities of both polymers into
account. A single expression of the interaction parameter based on the theory
of random copolymers provided a reasonable fitting of the experimental
cloud-point curves. The significant increase in the miscibility produced by
using small DMA molar fractions in the copolymer was explained by the high
negative value of the binary interaction energy between DMA and the epoxy-amine
solvent, associated to the positive value of the interaction energy between DMA
and MMA units. Block copolymers with poly(n-butyl acrylate) as the immiscible
block and the random copolymer P(MMA-co-DMA)
as the miscible block were used for the nanostructuration of DGEBA-DDS networks.
The necessary molar fraction of DMA in the miscible block to stabilize a
dispersion of nanosize domains depended on the fraction of the immiscible block
in the BCP.