The Ends of the Story

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Science  22 Jul 2011:
Vol. 333, Issue 6041, pp. 386
DOI: 10.1126/science.333.6041.386-a

The rich self-assembly behavior observed in block copolymer blends comes from joining two dissimilar polymers together and so forcing them to live next to each other. If the component blocks A and B are hydrophobic and hydrophilic, then placing the polymer in water can give rise to micelles, vesicles, or other morphologies, depending on the ratio of A to B. This behavior would not be expected of a homopolymer, with only one component. However, Du et al. observed the spontaneous formation of micelles when they put a number of homopolymers, synthesized using the reversible addition fragmentation chain transfer polymerization (RAFT) method, into acidic water. This polymerization technique uses chain transfer agents (CTAs) that make it possible to tune and tailor the end groups of the polymer chains, either during or after the synthesis. Aggregates formed only when hydrophobic groups were present on both ends of the polymers, though these constituted less than 2% of the weight, much less than what is usually needed for a block copolymer. One might expect this odd behavior to be limited to polyelectrolytes, where there is a strong interaction between the hydrophilic part of the polymer and the acidic water, and thus an additional driving force for the formation of aggregates, yet the authors also observed the formation of small micelles when a neutral polymer was used.

small 7, 10.1002/smll.201100382 (2011).

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