Supramolecular Aggregation of Block Copolymers in the Solid State As Assisted by the Selective Formation of Inclusion Crystals

Supramolecular self-assembly of a host molecule with selected blocks of triblock copolymers enabled the formation of inclusion 2D nanocrystals that connect consecutive copolymer chains. Indeed, the selective inclusion of ethylene oxide (EO) blocks in inclusion crystals and the phase segregation of PO blocks of poly(ethylene oxide-b-propylene oxide-b-ethylene oxide) (EOnPOmEOn) triblock copolymers provide an efficient route to create alternated crystalline lamellae and amorphous layers, forming a well-organized material. The spontaneous formation of the supramolecular architectures was realized by a solvent-free mechanochemical approach or by thermal treatment of the copolymer and host (tris-o-phenylenedioxycyclotriphosphazene), as demonstrated by in situ synchrotron X-ray diffraction. The driving force for the fabrication of crystalline inclusion compounds with selected EO segments is based on the establishment of cooperative noncovalent intermolecular interactions, while steric effects prevent the formation of the inclusion crystal with the remaining PO blocks. The 2D H-1-C-13 solid state and fast-H-1 MAS NMR provide direct evidence of the intimate interactions between the host and EO block and the topology of the block copolymer in the material. The large magnetic susceptibility generated by the aromatic host nanochannels surrounding the included EO chains was interpreted by ab initio calculations (HF-GIAO/DGDZVP) that carefully reproduce the chemical shifts associated with the effects of guest-host interactions. The theoretical calculations enable the measurement of short intermolecular distances between the host and the target block, demonstrating the existence of a diffuse network of multiple CH center dot center dot center dot pi host-guest interactions that improve the robustness of the supramolecular architecture. The overall evidence enforces the strategy of combining the use of block copolymers and clathrate-forming molecules to fabricate organized materials through noncovalent interactions.