Micelle Self-Assembly and Chain Exchange Kinetics of Tadpole Block Copolymers with a Cyclic Corona Block

A Prhashanna and EE Dormidontova, MACROMOLECULES, 53, 982-991 (2020).

DOI: 10.1021/acs.macromol.9b02398

Micelle self-assembly and chain exchange kinetics play an important role in technological applications such as biomedicine, cosmetics, etc. and remain an active area of research. In this work, using dissipative particle dynamics, we study the self-assembly and chain exchange kinetics of micelles formed by diblock copolymers with a cyclic hydrophilic block ("tadpole polymer") in comparison with that for micelles of linear diblock copolymers with the same hydrophobic block and the overall composition. We found that tadpole diblock copolymers form micelles of smaller sizes and aggregation numbers and exhibit quicker chain exchange compared to linear diblock copolymers. These changes are attributed to higher crowding of the hydrophilic cyclic block near the core-corona interface. This effect can be described within a simple scaling model, which predicts the micelle size and aggregation number decrease and area per chain increase for tadpole micelles in excellent quantitative agreement with the simulation results. Even the presence of a small fraction (20%) of cyclic hydrophilic blocks in the corona of mixed linear/tadpole micelles results in a micelle size decrease and alters the chain exchange kinetics. We observe that the chain exchange of individual components in mixed micelles exhibits synergy: exchange of tadpole chains slows down, while the linear chains speed up compared to the corresponding pure micelles, which correlates with the change in the area per chain. In contrast, mixed micelles containing linear chains of different hydrophilic block lengths do not show such a synergy and do not exhibit noticeable changes in the area per chain, indicating that the origin of the phenomenon is the cyclic corona chain architecture.

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