pH Dependence of the morphology of aqueous micelles formed by polystyrene-block-poly(2-vinylpyridine)-blockpoly( ethylene oxide) copolymers

Willet, Nicolas; Varshney, Sunil K.; Zhang, Jianxin; Jérôme, Robert

doi:10.1515/epoly.2002.2.1.517

“…Whenever N PS is higher than the average degree of polymerization of the PS block of the PS 200 -b-P2VP 140 -b-PEO 590 triblock (N PST ), an unstable milky solution (followed by precipitation) is formed upon water addition. In contrast, the addition of water to a DMF solution of the neat triblock results is an optically clear and stable solution of spherical micelles, that consist of a PS core, a P2VP shell and a PEO corona [6][7]. Precipitation is observed whenever water is added to a 0.05 wt% solution of PS 590 in DMF.…”

Section: Resultsmentioning

confidence: 97%

“…In this respect, well-defined coreshell-corona (CSC) micelles have been prepared from poly(styrene)-block-poly(2-vinylpyridine)-blockpoly(ethylene oxide) (PS-b-P2VP-b-PEO) triblock copolymers [6][7][8][9]. These micelles consist of a PS core, a pHresponsive shell and a PEO corona.…”

Section: Introductionmentioning

confidence: 99%

Morphology of core-shell-corona aqueous micelles: II. Addition of core-forming homopolymer

Liangcai

¹

,

Gohy

²

,

Willet

³

et al. 2004

Polymer

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The poly(styrene)-block-poly(2-vinylpyridine)-block-poly(ethylene oxide) triblock copolymer PS 200 -b-P2VP 140 -b-PEO 590 , where the subscripts refer to the number average degrees of polymerization, forms spherical micelles in water, that consist of a PS core, a pH-responsive P2VP shell and a PEO corona. This triblock has been added with homo-PS before micellization in order to increase the volume fraction of the core-forming block. The length of the added homo-PS has been varied with respect to the length of the PS core-forming block: much shorter, much longer and approximately the same. The structure of the micelles has been investigated by transmission electron microscopy, static and dynamic light scattering. Homo-PS phase separates whenever its length is larger than the one of the PS core-forming chains; otherwise this phenomenon occurs beyond a critical concentration that depends on molecular weight. The addition of homo-PS has no influence on the morphology of the micelles and on the characteristic size of both the PS core and the P2VP shell, although the hydrodynamic diameter of the micelles is decreased. Substitution of styrene for homopolystyrene results in transition from a spherical to a dominant rod-like morphology.

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“…Therefore, PS 590 also precipitates from the PS 590 /triblock solution in DMF, which indicates that it is not blended within the PS core of the micelles, as it is the case in the bulk [1]. [6][7] persists, as confirmed by the selective staining of the P2VP shell by phosphotungstic acid ( Fig. 3).…”

Section: Resultsmentioning

confidence: 97%

“…micelles. At pH>5, the P2VP shell is hydrophobic and collapses on the PS core, whereas it is positively charged, water-soluble and highly stretched at pH<5 [6][7]. Webber et al also studied the influence of pH on the micellization of P2VP-b-PEO diblocks.…”

Section: Resultsmentioning

confidence: 99%

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Morphology of core-shell-corona aqueous micelles: II. Addition of core-forming homopolymer

LEI

¹

2004

Polymer

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The poly(styrene)-block-poly(2-vinylpyridine)-block-poly(ethylene oxide) triblock copolymer PS 200 -b-P2VP 140 -b-PEO 590 , where the subscripts refer to the number average degrees of polymerization, forms spherical micelles in water, that consist of a PS core, a pH-responsive P2VP shell and a PEO corona. This triblock has been added with homo-PS before micellization in order to increase the volume fraction of the core-forming block. The length of the added homo-PS has been varied with respect to the length of the PS core-forming block: much shorter, much longer and approximately the same. The structure of the micelles has been investigated by transmission electron microscopy, static and dynamic light scattering. Homo-PS phase separates whenever its length is larger than the one of the PS core-forming chains; otherwise this phenomenon occurs beyond a critical concentration that depends on molecular weight. The addition of homo-PS has no influence on the morphology of the micelles and on the characteristic size of both the PS core and the P2VP shell, although the hydrodynamic diameter of the micelles is decreased. Substitution of styrene for homopolystyrene results in transition from a spherical to a dominant rod-like morphology.

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Fast Multiresponsive Micellar Gels from a Smart ABC Triblock Copolymer

Willet

¹

,

Gohy

²

,

Liangcai

³

et al. 2007

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Self-assembly of block copolymers in a solvent selective for one block is at the origin of unique behaviors of micellar particles, such as stimuli responsiveness. [1][2][3][4] ABC triblock copolymers are very versatile precursors of micelles, whose internal structure is dictated by the constitutive blocks and their sequential arrangement. Accordingly, smart materials can be contemplated, including multiresponsive ones. Herein, we report on pH-and temperature-sensitive gels formed by an amphiphilic ABC triblock copolymer, polystyrene-bpoly(2-vinylpyridine)-b-poly(ethylene oxide). The selfassembly of this copolymer into core-shell-corona (CSC) micelles [5,6] is observed in N,N-dimethylformamide upon addition of water. The micellar solution forms a soft gel at a lower threshold copolymer concentration (8 wt %) than other systems. [7][8][9] This soft gel is reversibly converted into an optically clear hard gel by merely decreasing the pH value or increasing the temperature. The ordered packing of the CSC micelles and the fast response to pH value were investigated by small-angle neutron scattering (SANS) and rheological measurements.Block copolymers consist of two or more chemically different polymer chains covalently bonded at their chain ends to form one single linear macromolecule.[10] The freeenergy-driven micellization of these copolymers takes place in a selective solvent, that is, a nonsolvent for one block and a good solvent for another. This self-association phenomenon is based on the phase separation of the insoluble blocks, which is, however, restricted to the nanometric scale by a surrounding shell of soluble blocks. Depending on the nature, length, and number of constitutive blocks and their interaction with the solvent, a variety of nanoobjects can be formed in dilute solutions, ranging from typical core-shell nanospheres [11][12][13] to cylinders, [12,14] vesicles, [12,15,16] and tubules, [16] as well as multilayered (onion), [5,17] non-centrosymmetric ("Janus"), and segregated structures. [18,19] Quite importantly, although less extensively studied, higher levels of organization can be observed, that is, assembly into clusters, networks, and gels. Stimulus-triggered aggregation of micelles has been reported for ABA triblock copolymers in a solvent selective for the B block, [9,[20][21][22][23][24] with special attention paid to the well-known polyoxyalkylene-type ABA copolymers (mainly Pluronics). [9,20,21] Among other responsive systems, Armes and coworkers synthesized biocompatible ABA triblocks, where A is poly(N-isopropylacrylamide) and B is poly(2-methacryloyloxyethyl phosphorylcholine).[24] Because of the thermosensitivity of the outer A blocks, micellization and ultimately gelation occurred above a lower critical solution temperature (LCST) of 37 8C. In recent years, increasing attention was paid to sol-to-gel transitions exhibited by multitalented ABC terpolymers. In addition to the synthesis of several isomers of a triblock terpolymer (ABC, BAC, and ACB) by Patrickios and co-workers that were...

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pH Dependence of the morphology of aqueous micelles formed by polystyrene-block-poly(2-vinylpyridine)-blockpoly( ethylene oxide) copolymers

Cited by 19 publications

References 12 publications

Morphology of core-shell-corona aqueous micelles: II. Addition of core-forming homopolymer

Morphology of core-shell-corona aqueous micelles: II. Addition of core-forming homopolymer

Morphology of core-shell-corona aqueous micelles: II. Addition of core-forming homopolymer

Fast Multiresponsive Micellar Gels from a Smart ABC Triblock Copolymer

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