The microstructure and mechanical properties of a block copolymer modified commercial thermoset plastic formed from a bisphenol‐A based epoxy and a bio‐derived amine hardener (Cardolite® NC‐541LV) were investigated. A series of poly(ethylene oxide)‐b‐poly(butylene oxide) (PEO‐PBO) diblock copolymers was synthesized at fixed composition (31 ± 1% by volume PEO) and varying molecular weight expanding on a commercially available PEO‐PBO compound marketed by the Dow Chemical Company under the trade name FORTEGRA™ 100; direct application of any of these block copolymers resulted in little improvement of the poor fracture toughness of the cured material. Modification of the resin formulation and curing protocol led to the development of well‐defined spherical and branched worm‐like micelles containing a PBO core and PEO corona in the cross‐linked products as evidenced by transmission electron microscopy (TEM) and small angle X‐ray scattering (SAXS) measurements. Maximum fracture toughness (K1c) and a ninefold increase in the critical strain energy release rate (G1c) over the unmodified neat epoxy was achieved at 5 wt % loading of intermediate molecular weight PEO‐PBO, without measureable reductions in modulus, glass transition temperature or transparency. This study provides new strategies for engineering improved performance in thermoset materials using block copolymer additives that exhibit challenging mixing thermodynamic characteristics with the component monomers. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016, 54, 189–204

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The ordering of a poly(styrene-b-butadiene) block copolymer solution into hexagonally packed cylinders during the extraction of a neutral solvent from a solution-cast film was studied in real time using in situ small-angle X-ray scattering (SAXS). By tracking changes in the scattering intensity as solvent is continually removed from the film, information on the ordering rate was obtained as the film progresses from the dilute to the concentrated regime. The ordering rate was found to be controlled by thermodynamics below a critical concentration and by limited chain mobility at higher concentrations. The effect of drying temperature on the ordering kinetics was investigated by extracting solvent at three different temperatures: 30, 40, and 60 °C. The net effect of drying temperature on the ordering rate was found to depend on a competition between the thermodynamics of the drying film and the mobility of the copolymer chains. An intermediate temperature, 40 °C, provided a balance between these competing phenomena, resulting in improved overall ordering in the films. The effect of drying rate was considered by drying films in the presence of a sweep gas. The introduction of a sweep gas to remove solvent resulted in appreciable concentration gradients that hindered ordering in the films.

Changes in the spacing of hexagonally packed cylinders in a poly(styrene-b-butadiene) copolymer film during the continual extraction of toluene under different solvent removal conditions were studied by in situ small-angle X-ray scattering (SAXS) measurements. As the solvent is removed from the film, the structure spacing increases due to increasing segregation power and then decreases as the polymer chains become kinetically trapped while microdomains continue to deswell. The structure spacing in the vertical film direction decreases more drastically due to compression of the domains as the film thickness decreases. The degree of compression increased with increased polymer concentration because of an increase in the chain relaxation time. Increasing the drying temperature resulted in more severe domain compression, which is ascribed to faster solvent removal. Removing solvent in the presence of a sweep gas further increased the domain compression as a result of the formation of a skin at the film surface. When the solvent removal rate was decreased and skinning was avoided by saturating the sample chamber with the casting solvent, domain compression was impeded.

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