Disassembly of Crystalline Platelets of an Amphiphilic Triblock Copolymer Mediated by Varying pH and Organic Diacids

Regulation of crystalline micelles is difficult to achieve because of the strong solidification of crystallization. In this present work, an amphiphilic triblock copolymer poly(ethylene oxide)- b -poly(ε-caprolactone)- b -poly(4-vinylpyridine) (PEO- b -PCL- b -P4VP) is prepared, in which the P4VP block serves as an H-bonding acceptor. It is originally self-assembled into crystalline lamellar micelles in aqueous solution. Subsequently, the effect of varying pH and organic diacids on morphological transition is investigated in detail. Lamellae-to-cylinder-to-sphere transitions are observed after decreasing the pH or with the addition of organic diacids with different chain spacers. The decreasing pH causes increasing hydrophilicity of the P4VP block, while adding organic diacids results in an increasing corona swelling of the P4VP segment, both of which lead to a decreasing crystallinity of the poly(ε-caprolactone) core. Consequently, morphological variety changing from lamellar to worm-like to spherical micelles can be achieved.