Abstract
This article reports a successful nanostructure formation from block copolymer having broad distribution of molecular weight. The block copolymer synthesis and the nanosphere formation are facile; therefore, it is promising for fabrication of nanostructure materials in large-scale manufactory. The polydisperse diblock copolymer of polystyrene-block-poly(4-vinyl pyridine) (PSVP) was prepared by the nitroxide-mediated radical polymerization that contains the fraction of poly(4-vinyl pyridine) block of 45 mol% and the overall polydispersity index of 2.08. The phase separation of PSVP was induced by the simple evaporation of co-solvent DMF:THF (70:30 v/v) of the PSVP solution. The SEM images of the self-assembled polydisperse PSVP display the spherical morphology with the diameter of ~ 50 nm, which is larger than that of block copolymer having narrow molecular weight distribution. By simply immersing the self-assembled film into iron chloride solution, the transformation from the spherical structure to the porous structure occurred directly without sacrificing the block copolymer component indicating the advantage of stimuli-response properties of the self-assembled PSVP. The results demonstrated that the polydisperse block copolymer could be used for the nanostructure formation by simple synthesis and evaporation procedures and, therefore, it is suitable for industrial applications.Graphical
Highlights
Microphase separation of the amphiphillic block copolymer (BCP) of polystyrene‐block‐poly(4‐vinyl pyridine) (PSVP), which is driven by the strong repulsive interaction between the non-polar polystyrene (PS) block and the polar poly(4-vinyl pyridine) (P4VP) block, generates the various morphologies at nanometer scale such as sphere, cylinder, lamellar, and gyroid
In the large-scale or in the industrial synthesis, the self-assembly process for nanostructure morphologies is difficult because the molecular weight distribution (MWD) of the polymer is broader than that synthesized in the ideal laboratory conditions [11]
Since TEMPO is a stable free radical, high temperature is required for the activation/deactivation of the growing radical chains during the TEMPO-mediated radical polymerization, but most of polymerization temperature was induced at 125–135 °C to avoid the homolysis of alkoxyamine [25]
Summary
Microphase separation of the amphiphillic block copolymer (BCP) of PSVP, which is driven by the strong repulsive interaction between the non-polar polystyrene (PS) block and the polar poly(4-vinyl pyridine) (P4VP) block, generates the various morphologies at nanometer scale such as sphere, cylinder, lamellar, and gyroid. Strategies to approach the polydisperse BCP are either by blending of block copolymers/homopolymer having different molecular weight [13,14,15] or by adjusting the polymerization conditions [16,17,18] of CRP. The latter is considered closer to the nature of BCP structure in the large-scale industrial process [12]. The morphology of nanostructure was observed from FE-SEM images (FE-SEM S4800, Hitachi, Japan)
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