Co-assembly of block copolymers (BCPs) and organic/inorganic additives affords the design of various hierarchical nanostructures. In this work, we investigate the shape-changing capabilities of poly(styrene-block-2-vinylpyridine) (PS-b-P2VP) BCP particles upon quaternization with a series of bromoalkyl benzene additives with different alkyl spacer lengths. The bromoalkyl benzene additives exhibit different hydrolyzing and quaternizing behaviors depending on their chemical structures. When benzyl bromide (BB) is used, the PS-b-P2VP BCP particles exhibit dramatic shape transitions from ellipsoids to ellipsoids with swelled discs, swelled buds, and vesicles. These morphological transitions are attributed to the synergistic quaternization and protonation of the P2VP chains via the hydrolysis of BB in aqueous media. Upon increasing the molar ratio of BB to 2VP units, the pH of the surrounding aqueous solutions significantly decreases, and the protonated P2VP domains are swelled by the surrounding water, which eventually results in interfacial instability of the emulsion interface. When the additives contain longer alkyl spacers (e.g., ethyl, butyl, and hexyl), the additives lead to a narrower range of quaternization-dependent particle morphologies due to the absence of the hydrolysis of the additives. However, a broader spectrum of particle shapes is observed for additives with longer alkyl chains, due to their stronger quaternizing capabilities. We carefully investigate the structural effect of the quaternizing additives on the change of pH, degree of quaternization, and interfacial tension to elucidate the mechanism of the additive-driven particle morphology transitions.
Synthesis of brush block copolymers (brush BCPs) enables the generation of BCPs with various block compositions and chain architectures, which determine the morphologies and functionalities of the polymeric materials. Here, we report a synthetic strategy for preparing structurally diverse brush BCPs via combined synthesis of the grafting-through and grafting-to approach. The polystyrene-based brush copolymer with an azide functionality is synthesized by sequential ring-opening metathesis polymerization of norbornene-based macromonomers, followed by post-polymerization modification. The final brush BCPs are then prepared by grafting various side chain polymers [poly(2-vinylpyridine), poly(4-vinylpyridine), or poly(dimethylsiloxane)] onto the precursor BCPs with the desired ratio between the azido group on the backbone and alkynyl side chain polymer. This synthetic method is versatile in producing brush BCPs with various side chain types, backbone lengths, and grafting densities. In particular, it is observed that the morphologies of the brush BCPs can be controlled from lamella to cylinders to spheres by tuning the grafting densities. Furthermore, this interesting transition of self-assembled morphologies of the brush BCPs at different grafting densities is elucidated by the simulation results.
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