Unique Interphase and Cross-Linked Network Controlled by Different Miscible Blocks in Nanostructured Epoxy/Block Copolymer Blends Characterized by Solid-State NMR

A variety of multiscale solid-state NMR techniques were used to characterize the heterogeneous structure and dynamics of the interphase and cross-linked network in nanostructured epoxy resin/block copolymer (ER/BCP) blends, focusing on the role of ER-miscible blocks containing poly(epsilon-caprolactone) (PCL) or poly(ethylene oxide) (PEO) blocks having different intermolecular interactions with ER. H-1 spin-diffusion experiments indicate that the interphase thickness of PEO-containing blends is obviously smaller than that of PCL-containing blends. High-resolution H-1 fast magic-angle spinning (MAS) spin-exchange experiments reveal detailed interfacial mixing between ER and BCPs for the first time, and two different types of interphase structure are found. fast MAS double-quantum filter experiments provide a fast and convenient detection of interphase composition, including immobilized BCPs and partially cured or local damaged ER network. The driving force for the interphase formation and miscibility in PCL-containing blends was successfully determined by high-resolution C-13 CPMAS experiments, demonstrating the formation of hydrogen bonds between PCL and ER; competing hydrogen bonding interactions were also found when ER was blended with PEO-b-PCL (EOCL). A new calculation method is proposed to quantitatively determine the distribution of different blocks in the interphase and dispersed phase for PCL-containing blends in combination with C-13 CPMAS and H-1 spin-diffusion experiments. A C-13 T-1, spin lattice relaxation experiment provides a quantitative determination of the amount of local destroyed network in the interphase. Furthermore, it is found that incorporation of BCPs induces unexpected enhanced rigidity of the cross-linked network. On the basis of NMR results, we propose a model to describe the unique structure and dynamics of the interphase and cross-linked network as well as their underlying formation mechanism in ER/BCP blends.