Amphiphilic miktoarm star copolymers can self-assemble into micelle-like aggregates in nonselective solvents: a case study of polyoxometalate based miktoarm stars

It is well-known that amphiphilic star-shaped copolymers can self-assemble in selective solvents to form complicated micellar constructs as a synergistic result of both the topological constraints and relative volume fractions of the arms. Although the association phenomena of amphiphilic stars have been observed in nonselective solvents, both the structural detail and formation mechanism of these associates are not clear yet. Moreover, these experimental observations are controversial with respect to molecularly dispersed starlike copolymers in nonselective solvents as is popularly believed. To clarify these issues, we have synthesized a series of polyoxometalate-based polystyrene-poly(ethylene glycol) (PS-PEG) miktoarm star supramolecular copolymers (SEW-1-5) by coupling a Keggin-type polyoxometalate of K4[α-SiW12O40] with 1,2,3-triazolium bridged block copolymers of PSn-b+-PEGmI− (n=17, 26, 39, 57, 81; m=45) through ionic exchange reactions, respectively. TEM imaging, contact angle and 1H NMR studies reveal that SEW-2-5 self-assemble in chloroform, THF, and toluene to create micellelike aggregates ranging from cylinder to sphere with a PS corona and a PEG core, while for SEW-1, reverse bilayers are captured with a PEG corona and a PS core. Among these aggregates, the Keggin clusters of [α-SiW12O40]4− localize at the core-corona interfaces between PS and PEG. In terms of solvent quality, chloroform, THF, and toluene are only slightly poorer for PEG than that for PS with a relative order of chloroform

Keywords:

• Organic chemistry
• Stars
• Amphiphile
• Chemical engineering
• Chemistry
• Polyoxometalate
• Micelle
• Copolymer
• self assemble

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