Thermosetting resins were synthesized by the partial replacement of the synthetic epoxy prepolymer based on diglycidyl ether of bisphenol A (DGEBA) with increasing amounts of epoxidized soybean oil (ESO) with methyltetrahydrophthalic anhydride as a crosslinking agent and 1-methyl imidazole as an initiator. Calorimetric studies showed a drop in the reaction heat with ESO content; this was associated with the lower reactivity of oxirane rings in ESO due to steric constrains. The effects of the replacement of increasing amounts of synthetic DGEBA with ESO on the network properties, such as the storage modulus (E 0 ) in the glassy and rubbery regions, glass-transition temperature (T g ), and impact and compressive properties were examined. All formulations were transparent, although phase-separated morphologies were evidenced by scanning electron microscopy observations. The intensity of the transmitted light passed to a minimum at a short reaction time associated with the cloud point and then increased continuously until the refractive index of the dispersed phase approximated that of the continuous phase at complete conversion. The combination of DGEBA with 40 wt % ESO resulted in a resin with an optimum set of properties; E 0 in the glassy state was 93% of that of the neat DGEBA resin, T g decreased only about 11 C, and the impact strength increased about 38% without a loss of transparency. V C 2010 Wiley Periodicals, Inc.J Appl Polym Sci 120: [789][790][791][792][793][794][795][796][797][798] 2011
The gradient on block copolymer concentration through
film thickness as well as the effects of casting solvents used on
the nanostructuring of a thermosetting epoxy coating modified with
an epoxidized poly(styrene-b-butadiene-b-styrene) (SBS) triblock copolymer was studied by means of atomic
force microscopy and attenuated total reflectance infrared spectroscopy.
Thin coating films based on a commercial epoxy– amine formulation
consisting of diglycidyl ether of bisphenol A and a low-temperature
fast curing amine were modified with several amounts of epoxidized
SBS triblock copolymer. Toluene and a mixture of tetrahydrofuran and N,N-dimethylformamide were used as casting solvents. With
epoxidation degrees higher than 45 mol % of polybutadiene block nanostructuring
was achieved. Fast curing rate of the epoxy/amine system and the comparatively
slow evaporation rate of the casting solvent led to a gradient of
morphologies through the film cross section owing to the coalescence
of small micelles into larger micellar domains in the case of low
block copolymer content. For these reasons, different morphologies
were also obtained in the midtransverse section of a film with variable
thickness. Finally, pseudolamellar nanostructure at high copolymer
contents was achieved as confirmed by parallel and perpendicular cuttings
to the air/polymer interface.
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