Controlling the generation of bilayer and multilayer vesicles in block copolymer/epoxy blends by a slow photopolymerization process

PUIG, J.; CEOLÍN, M.; WILLIAMS, R. J. J.; SCHROEDER, W. F.; ZUCCHI, I. A.

SOFT MATTER

ROYAL SOC CHEMISTRY

Lugar: CAMBRIDGE; Año: 2017 vol. 13 p. 7341 - 7351

1744-683X

Vesicles are a highly attractive morphology to achieve in micellar dispersions of block copolymers (BCP)in epoxy thermosets due to the fact that small amounts can affect a large volume fraction of the matrix, a fact that is important for toughening purposes. However, generating vesicles in epoxy matrices requires operating in a narrow range of formulations and processing conditions. In this report, we show that block-copolymer vesicles dispersed in an epoxy matrix could be obtained through a sphere-tocylinder-to-vesicle micellar transition induced by visible-light photopolymerization at room temperature.A 10 wt% colloidal solution of poly(ethylene-co-butene)-block-poly(ethylene oxide) (PEB-b-PEO) block copolymer (BCP) in an epoxy monomer (DGEBA) self-assembled into spherical micelles as shown by small-angle X-ray scattering (SAXS). During a slow photopolymerization of the epoxy monomer carriedout at room temperature, a sphere-to-cylinder-to-vesicle transition took place as revealed by in situ SAXS and TEM images. This was driven by the tendency of the system to reduce the local interfacial curvature as a response to a decrease in the miscibility of PEO blocks in the polymerizing epoxy matrix.When the BCP concentration was increased from 10 to 20 and 40 wt%, the final structure evolved from bilayer vesicles to multilayer vesicles and to lamellae, respectively. In particular, for 20 wt% PEB-b-PEO, transient structures such as partially fused multilayered vesicles were observed by TEM, giving insightinto the growth mechanism of multilayer vesicles. On the contrary, when a relatively fast thermal polymerization was performed at 80 1C, the final morphology consisted of kinetically trapped spherical and cylindrical micelles. Hopefully, this study will lead to new protocols for the preparation of vesiclesdispersed in epoxy matrices in a controlled way.