INVESTIGADORES
ARANGUREN Mirta Ines
artículos
Título:
Polyurethane ductilized epoxy resins
Autor/es:
STEFANI, PABLO M.; MOSCHIAR, STELLA M.; ARANGUREN, MIRTA I.
Revista:
JOURNAL OF APPLIED POLYMER SCIENCE
Editorial:
Wiley
Referencias:
Lugar: NY; Año: 1998 vol. 68 p. 1781 - 1789
ISSN:
0021-8995
Resumen:
ABSTRACT: Amine-cured epoxy resins were modified to improve their impact properties.
Urethane prepolymers (PUs), in which terminal isocyanate groups were blocked with
nonylphenol (NP) for easy handling, were used as modifiers. The synthesis of the
elastomers were carried out at different NCO : OH ratios: 1 : 1, 2 : 1, and 3 : 1 (PU1,
PU2, and PU3). Characterization of these materials by GPC and FTIR indicated that
PU1 has a negligible amount of NCO-terminated chains and no unreacted toluenediisocyanate
(TDI). PU2 and PU3 have free-blocked TDI in the mixture, even after distillation
under a vacuum. The molecular weight and polydispersity of the prepolymer increases
as PU3 PU2 PU1. Copolymerization was carried out by crosslinking with
a mixture of cycloaliphatic amines, which react with the epoxy ring and with the NCO
groups by deblocking and urea formation. Dynamic mechanical tests were used to
measure the glass transition temperatures (Tg ) of the copolymers. Two Tg were found
if PU1 was the epoxy modifier, indicating that phase separation took place. This was
correlated with a structure of PU1 of linear chains with a negligible amount of reactive
groups. Flexural and compression properties showed negligible changes for PU2- and
PU3-modified epoxy, but the critical strain energy release rate (G1C) was improved if
PU2 was the modifier. This behavior was explained by the linkage of elastomeric chains
into the epoxy network. The PU1epoxy copolymer showed a completely different behavior,
with the bending modulus (Eb ) reduced to almost one-half with respect to that
of the epoxy matrix and with largely improved impact properties. This difference was
attributed to the separation of an elastomeric phase, which favors the formation of
shear bands in the epoxy matrix. q 1998 John Wiley & Sons, Inc. J Appl Polym Sci 68: 1781
1789, 1998
Key words: modified epoxy; urethaneepoxy copolymers; blocked urethane prepolymer;
fracture