Tailoring of the hierarchical structure within electrospun fibers due to supramolecular comb-coil block copolymers: polystyrene-block-poly(4-vinyl pyridine) plasticized by hydrogen bonded pentadecylphenol

Abstract

Previously we demonstrated hierarchical self-assembly and mesoporosity in electrospun fibers using selected polystyrene-block-poly(4-vinylpyridine) (PS-b-P4VP) diblock copolymers with hydrogen-bonded 3-n-pentadecylphenol (PDP), which rendered distorted spherical P4VP(PDP)_1.0 domains within the PS matrix, internal lamellar order within the P4VP(PDP)_1.0 domains, and allowed distorted spherical pores by removing PDP (Adv. Mater. 2005, 17, 1048). Here we study whether the internal structure of electrospun fibers can be systematically tailored by varying the compositions of PS-b-P4VP(PDP)_1.0. We expect these complexes to be feasible choices to combine electrospinning and self-assembly, as relatively high molecular weight block copolymers are useful for electrospinning, and enhanced structure formation due to plasticization by the amphiphilic PDP was expected. Not surprisingly, the self-assembled structures of the as-prepared fibers were less perfect than those in the corresponding well-annealed bulk materials. Compositions that show spherical self-assembly of P4VP(PDP)_1.0 within the PS matrix in bulk lead to distinct and elongated worm-like P4VP(PDP)_1.0 domains within the PS matrix in electrospun fibers. More symmetric compositions, which showed lamellar self-assembly in bulk, lead to structures where both PS and P4VP(PDP)_1.0 domains were worm-like and elongated in a relatively symmetric manner. Finally, compositions which in bulk showed self-assembly of PS spheres within the P4VP(PDP)_1.0 matrix, lead to separate distorted PS domains in the P4VP(PDP)_1.0 matrix. Additionally, SAXS measurements suggest a lamellar structure within the P4VP(PDP)_1.0 domains. As electrospinning is a facile method to prepare mesoscale fibers, and it is known that the amphiphiles can be removed from the hierarchical assemblies, the present method offers the potential to tune the internal porosity of the fibers for e.g. release and absorption purposes.