Morphological Transition of Aggregates from ABA Amphiphilic Triblock Copolymer Induced by Hydrogen Bonding

Abstract

The hydrogen-bonding-induced aggregate morphological transition of the triblock copolymer poly(4-vinylpyridine)43-b-polystyrene366-b-poly(4-vinylpyridine)43 (P4VP-b-PS-b-P4VP) in dilute solution was studied by introduction of a surfactant (pentadecylphenol, i.e., PDP) into the solution. The P4VP-b-PS-b-P4VP triblock copolymer exhibits spherical aggregates in 1 wt % of the surfactant (PDP)-free solution. However, the aggregate morphologies changed from short rods to networks and looped structures and then to vesicles and compound vesicles by increasing PDP content at the same copolymer concentrations to the PDP-free solutions. The striking feature is that a trace amount of PDP (molar ratio of 4VP/PDP = 1000) addition can change the aggregate morphologies to wormlike morphologies. The nature of the influence that PDP exercise over the copolymer aggregates was determined by comparing the results with those obtained for the addition of the m-cresol (without the long tail of linear alkyl) and pentadecylbenzene (without hydroxyl). The interactions of both the hydrophobic chain and the hydrogen bonding of the PDP headgroup with the block copolymer molecules affect the architecture of the copolymer aggregates. Hydrogen bonding weakens the interaction among the corona-building blocks, and hydrophobic chains of the PDP insert into the core of the aggregates, leading to the increases of the core dimension of the aggregates. The latter effect is more important on the morphological transition, which has been proved in experiment. Using the hydrogen bonds of block copolymers with small molecular amphiphiles opens up the possibility of reaching a certain fraction to produce a desired aggregate morphology, representing another tool for manipulation of these nanostructures.