Block copolymers self-assemble in bulk forming various intricate nanometer-sized block segregation patterns.1 Block-segregated solids of diblock copolymers have been processed chemically in the past to yield nanofibers,2, 3, 4, 5 nanospheres,6 nanochannels in thin films,7, 8 inorganic nanoparticles in polymer matrices,9, 10, 11, 12 and photolithographic masks with nanometer-sized patterns.13 Linear triblocks AnBmCl, where A, B, and C denote different monomers, are far richer in block segregation patterns than diblocks. Despite this, there have been only a few reports of nanostructure preparation from block-segregated triblock solids. Here we report the preparation of polymer/Fe2O3 hybrid nanofibers from processing films of a triblock copolymer polystyrene-block-poly(2-cinnamoyloxyethyl methacrylate)-block-poly(t-butyl acrylate) or PS-b-PCEMA-b-PtBA. Also to be reported will be the superparamagnetism of the hybrid nanofibers and their alignment in magnetic fields.
The preparation involved the self-assembly of the blocks in thin films into concentric PCEMA and PtBA cylinders dispersed in the matrix of PS (A-->B of Scheme 1). The cylindrical structures were then locked in by photo-crosslinking the PCEMA shells (B-->C). Dissolving the films in THF yielded individual nanofibers with PS coronas, PCEMA middle layers, and PtBA cores (C-->D). Nanotubes with poly(acrylic acid)- or PAA-lined cores were obtained after cleaving the t-butyl groups from PtBA (D-->E). Producing Fe2O3 nanoparticles in the PAA cores yielded solvent-dispersible superparamagnetic block copolymer/inorganic hybrid nanofibers (E-->F).
For a review on triblock morphologies, see, for example, F. S. Bates, G. H. Fredrickson Phys. Today1999, February issue, 32.
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