Epoxy thermoset blended with polystyrene-block-polybutadiene-block-poly(methyl methacrylate) triblock copolymers have been investigated before and after the epoxy-amine reaction, coupling different techniques: dynamic mechanical thermal analysis (DMTA), transmission electron microscopy (TEM) and small-angle X-ray scattering (SAXS). Before reaction, the three blocks self-organize on a nanometer scale, in PS spheres surrounded by PB nodules while the PMMA blocks are solubilized with the epoxy precursors, forming a swollen corona. Using MCDEA as hardener, the domain sizes were found not to be affected throughout the network formation. The final structure is composed of undiluted PS and PB blocks forming a "spheres on spheres" morphology, most of the PMMA chain remaining embedded in the epoxy network. A partial deswelling of the PMMA brush does occur during the epoxy-amine reaction, resulting in a pure PMMA phase. This phase, evidenced by DMTA, is most likely located at the vicinity of the interface with the PB microdomains. On the other hand, using DDS as hardener induces the phase separation of the PMMA blocks in the early stages of reaction, leading to flocculated, micrometer size elongated nanostructures and opalescent materials. Transparent nanostructurated thermosets were obtained when the following requirement was met: that the PMMA homopolymer remained soluble within the growing thermoset polymer during the whole reaction. The effects of "impurities" on the triblock behavior have also been studied and compared to the effects of "impurities" on a diblock behavior.

The effect of composition and concentration of polystyrene-block-polybutadiene-block-poly-(methyl methacrylate) (SBM) copolymer triblock on final morphologies and properties of modified epoxy networks has been investigated. The DGEBA-MCDEA epoxy system, which ensures the miscibility of most of the PMMA blocks until the end of the reaction and thus the generation of a nanostructurated material, has been chosen. For low copolymer concentration (10 wt %), the network structure is found to be independent of the composition and micelles of PS and PB blocks can be undifferently observed. However, increasing copolymer amounts from 10 to 50 wt % induces a morphology change to either "spheres on spheres" or "core-shell" structure depending on the PB content in the triblock. For copolymer concentration higher than 50 wt %, the morphology strongly depends on the processing technique used, and only films prepared by solvent casting show an organization with long-range order similar to the neat block copolymer. The toughness of nanostructured epoxy networks has been evaluated. For low SBM concentration the toughness was observed to linearly vary with the PB concentration. For higher SBM concentrations (30 and 50 wt %) the "spheres on spheres" morphology is found to be more efficient than the "core-shell" one to improve the toughness of the epoxy network. But in all cases a higher toughness is obtained when the nanostructure is preserved; when a macrophase separation occurs, the toughness increase is lower.

Polystyrene-block-polybutadiene-block-poly[(methyl methacrylate)-stat-(methacrylic acid)] (SB(MA)) block copolymers incorporating acid-reactive functionalities in the last block have been synthesized and studied as modifiers for epoxy thermosets based on the diglycidyl ether of bisphenol A (DGEBA). Different techniques including differential scanning calorimetry (DSC), Fourier transform infrared spectroscopy (FT-IR), and transmission electron microscopy (TEM) have been used to demonstrate the effectiveness of the reaction-induced modification compared to that with the nonreactive or slowly reacting polystyrene-block-polybutadiene-block-poly[(methyl methacrylate)-stat-(tert-butyl methacrylate)] SB(MT) triblock copolymer. Morphological characteristics revealed by TEM indicate that SB(MT) and SB(MA) are both miscible with the epoxy prepolymer. The kinetics of grafting, network formation, and possibly phase separation were quantified from FT-IR, DSC, and cloud point investigations of DGEBA/ DDS (4,4′-diaminodiphenyl sulfone) as an epoxy-thermoset model system in the presence of poly[(methyl methacrylate)-stat-(methacrylic acid)] (HT121) or the block copolymers. The cure of the thermoset/block copolymer system has been explored using six different curing processes: 2-phenylimidazole (2-PI), alone or in the presence of methyltetrahydrophthalic anhydride (MTHPA) as comonomer, accelerated dicyandiamide (DICY), and three different diamines as comonomers without accelerator: 4,4′-methylenebis(3chloro-2,6-diethylaniline) (MCDEA), 4,4′-methylenedianiline (MDA), and DDS. The use of reactive block copolymers instead of nonreactive ones permits a better control of morphology. The materials' performances are analyzed in terms of transparency, glass transition temperature, T g, and linear elastic mechanics at break (critical intensity factor, KIC).