Modification of epoxy resins with block copolymers of poly(ethylene oxide) and poly(butylene oxide).

Block copolymer modified epoxy resins have generated significant interest since it
was demonstrated that the combination could lead to nanostructured thermosets
through self-assembly.
In this work, samples of epoxy resin - formed by reaction of bisphenol-A diglycidyl
ether (BADGE) and diethyltoulenediamine (DETDA) - and containing a range of
copolymers composed of poly(ethylene oxide) (E) and poly(butylene oxide) (B),
were prepared and characterized. Samples contained EB, EBE and BEB copolymers
over a range of concentrations. Copolymers of low molecular weight and low B
content were found not to microphase separate. BEB copolymers with high
molecular weight and high B content were found to macrophase separate prior to, or
during, cure.
FTIR spectroscopy during cure demonstrated that the reaction kinetics in these
systems differ from those previously reported for similar systems.
Over moderate to high copolymer concentration the systems behaved as expected of
a block copolymer in a solvent selective for one block. As concentration increased,
transitions from BCC-Hex-Gyr-Lam phases were observed by SAXS.
At lower concentrations, in some systems, spherical micellar structures were formed,
as demonstrated by TEM. SAXS analysis was performed on those systems producing
sufficiently clear patterns. Some degree of reaction-induced microphase separation
(RI/lPS) was observed in all cases. A linear increase in scattering intensity with
extent of reaction was observed during RI/lPS. In some cases non-equilibrium
structures were apparently observed, due to vitrification prior to completion of the
RI/lPS process. The increase in the number of micelles as a function of concentration
was analyzed and found to deviate from linearity as the system goes from a solution
of copolymer in epoxy to swollen copolymer gel. The association number of the
micelles was found to vary as a function of copolymer composition following a
similar scaling law to that observed, by others, in aqueous solution.
Reaction-induced macrophase separation was observed in some BEB systems at
elevated temperature, but not in similar EBE systems. The process was characterised
by SALS and found to fit to the Cahn-Hilliard linear theory of spinodal
decomposition. The systems were seen to vitrify before phase separation is complete,
producing cured products that were phase separated into interpenetrating networks
on the micron scale.
No significant improvement of mechanical properties of the resin was observed in
those samples tested.