Self-Assembly of Formic Acid/Polystyrene-block-poly(4-vinylpyridine) Complexes into Vesicles in a Low-Polar Organic Solvent Chloroform

Abstract

Self-assembly of block copolymers in solutions and the resultant polymeric nano-objects have attracted considerable interest in both theoretical and applied research fields. [1][2][3][4][5][6][7] Recently, a number of studies on the selfassembly of complexes of block copolymers/low-molecular mass compounds (LMC, including surfactants and other molecules with a polar head and a nonpolar tail) were reported. Since the relative amount of LMC and the binding are adjustable, Ikkala et al. used the complexes to prepare materials with different morphologies and onoff properties in bulk. [8][9][10][11] In aqueous media, the selfassembly of the complex of LMC and a block copolymer may result in vesicles alone, 12,13 micellar clusters, or precipitation, 14 depending on the dispersion state of the block copolymer in water before mixed with LMC. However, in low-polar organic solvents in which the nonpolar tails of LMC are soluble, the self-assembly leads to different results. 15,16 The block copolymers capable of forming complexes with LMC contain at least one block with a certain number of polar groups, so the binding with LMC usually increases their solubility in low-polar organic solvents. 16 Therefore, no regular aggregates resulting from the self-assembly of the complexes of LMC and block copolymers in organic solvents have been reported. This brought up a question to us, i.e., what would the complexes behave like in the low-polar organic solvents if we reduce the length of the lipophilic tails of LMC or even remove them? We studied the complexation of polystyrene-b-poly(4-vinylpyridine) (PS-b-P4VP) with linear aliphatic acids in chloroform. The results show that the resultant complexes may self-assemble to form nanosized aggregates (vesicles) or exist in a molecularly dispersed state, depending on the length of the aliphatic chains.Chloroform is a common solvent for the block copolymer PS-b-P4VP, as well as a solvent for stearic acid (SA), decanoate (DA), acetic acid (AA), and formic acid (FA). When PS-b-P4VP (the weight average molecular weights of the PS and P4VP blocks are 33 000 and 29 000 respectively; the M w /M n of the block copolymer is 1.37) was mixed with SA, DA, and AA in chloroform, the mixture solutions remained transparent. However, 13 C NMR spectra of the mixtures in deuterated chloroform show that the peak associated with the carbon atoms in the carboxyl of the acids shifts from 178.0 to 175.5 ppm. In addition, in the spectra of the stoichiometric mixtures, no signals of the acids in the unbound state were detected. These results indicate that the copolymer can form soluble complexes with the aliphatic acids SA, DA, and AA and that in the stoichiometric mixtures almost all the carboxyl groups of the acids bind with the pyridine groups. In other words, the complexation is irreversible. This agrees with the results obtained by Ikkala et al. on the complexation between P4VP and 3-pentadecylphenol. 9,17,18 When the solutions of the complexes of PS-b-P4VP with SA, DA, and AA in chloroform were characterized...

Solvent Influence on Thickness, Composition, and Morphology Variation with Dip-Coating Rate in Supramolecular PS-b-P4VP Thin Films

“…It is known that PS− P4VP diblock copolymers form micellar solutions in THF, toluene, and p-dioxane due to the insolubility of the P4VP block in these solvents 35,36,47 (except for low molecular weight P4VP in THF), whereas CHCl 3 , as a good solvent for both blocks, does not lead to micellar solutions. 48 In the context of the present study and given literature reports that small molecules that are hydrogen-bonded to one of the blocks can alter the solubility behavior of block copolymers, 17,48−51 it is of interest to determine if the addition of NOH or NCOOH has an influence on the micellar characteristics and how the micellar rigidity varies among the solvents. This was addressed by static and dynamic light scattering (SLS and DLS) experiments to obtain the radii of gyration, R g , and the hydrodynamic radii, R h , respectively.…”

Successful ATRP Syntheses of Amphiphilic Block Copolymers Poly(styrene-block-N,N-dimethylacrylamide) and Their Self-assembly

“…The polymer vesicles with a hollow structure have been self-assembled using block copolymers with an amphiphilic structure. [7][8][9][10] Our particular interests have concentrated on the amphipathic structure where polystyrene (PSt) block as a hydrophobic segment and polyacrylamide derivatives as a hydrophilic segment, since PSt is one of the most hydrophobic polymers having a strong -stacking interaction while the latter polymers are one of a widely-used water-soluble polymers which have high advantages for developing the biomedical materials. Especially, polydimethylacrylamide (PDMAA) is sensitive to a change in aqueous milieu due to the secondary amino side group.…”

Self-assembly of pH-sensitive random copolymers: Poly(styrene-co-4-vinylpyridine)

“…However, after the deuterated DMF solution of PSVP36 was added dropwise into pH 2 deuterated water, the 1 H NMR spectrum of PSVP36 exhibits significant broadening and weakening of these signals (Fig. 3, curve 2), which indicates that the motions of benzene and pyridine groups are highly restricted [28,29]. This result clearly suggests the aggregation of these groups in acidic aqueous solution [28,30].…”