Association of Block Copolymer in Nonselective Solvent

Abstract

The behavior of poly(ethylene oxide)-block-poly(N,N-dimethylacrylamide) (PEO-b-PDMA) in aqueous solution at dilute concentrations was studied by laser light scattering. Even though water was a nonselective solvent for both PEO and PDMA blocks, PEO-b-PDMA formed a certain loose associate in aqueous solutions. Different from the micellization of block copolymers in selective solvents, the association of PEO-b-PDMA in aqueous solution showed weak concentration and temperature dependence as well as opposite salt effect. At 4.0 M NaCl, the association was completely suppressed and PEO-b-PDMA existed as individual polymer chains. This opposite “salting out” effect revealed the association mechanism of block copolymers in nonselective solvent: the solubility of PEO block in aqueous solution was unique, and it exhibited a better hydrophilicity and thick hydration shell than other water-soluble polymers. This inequality or weak incompatibility drove the block copolymer to associate into loose structures containing multidomains rich of either blocks. The dependence of the association on the block ratio also supported our conclusions.

Synthesis and Solution Properties of Double Hydrophilic Poly(ethylene oxide)-block-poly(2-ethyl-2-oxazoline) (PEO-b-PEtOx) Star Block Copolymers

“…Such behavior has also been described for water-soluble homo-and block copolymers in the literature [12,19,[56][57][58]. In some cases, the unexpected aggregation of double-hydrophilic block copolymers was explained by slight differences in the hydrophilicity of both blocks [50,58].…”

“…However, as this effect was only observed for star-shaped block copolymers prepared via the "arm first" approach and only if non-filtered solutions were used, we hypothesize that a certain pre-organization is required. The aggregation behavior of PEO depending on the treatment before was also discussed by Güner et al for linear polymers [56], and differences in hydrophilicity were described by Ke et al [50,60]. …”

“…To ensure full end-group conversion of the modified star-shaped macromolecules, the polymers were investigated via 13 C-NMR and 2D-LC (LCCC × SEC). In the latter case, liquid chromatography under critical conditions for PEO (LCCC) should enable the separation according to the end-group polarity and further coupled to SEC for the molar range [49][50][51][52][53]. After careful adjustment of the critical conditions for PEO (Figure S2), the stars with different end-groups ([PEO 28 -OH] 8 , [PEO 28 -Ts] 8 and [PEO 28 -N 3 ] 8 ) were investigated ( Figure 1).…”

PEG‐Amine‐Initiated Polymerization of Sarcosine N‐Thiocarboxyanhydrides Toward Novel Double‐Hydrophilic PEG‐b‐Polysarcosine Diblock Copolymers

“…PEG‐ b ‐PSar block copolymers are effective emulsifiers for organic droplets in water. The driving force of DHBC association in aqueous solution is the incompatibility between the two blocks, majorly caused by their different capacities to interact with water molecules . Based on Luxenhofer's report that PSar appears to be miscible with water in all ratios (for DP < 100), PSar is more hydrophilic than PEG.…”

Double Hydrophilic Block Copolymer Self‐Assembly in Aqueous Solution

“…Therefore, larger amounts of polymers are needed to allow the formation of hollow structures. Liang and co‐workers utilized PEO‐ b ‐poly( N , N ‐dimethylacrylamide) (PEO‐ b ‐PDMA) for aqueous self‐assembly at concentration around 0.6–2.0 wt% . A thorough characterization was conducted via DLS and SLS showing apparent hydrodynamic radii of ≈150 nm.…”