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| Hauptseite > Publikationsdatenbank > Dual Orthogonal Switching of the “Schizophrenic” Self-Assembly of Diblock Copolymers |
| Hauptseite > Publikationsdatenbank > Dual Orthogonal Switching of the “Schizophrenic” Self-Assembly of Diblock Copolymers |
| Journal Article | FZJ-2018-06078 |
; ; ; ; ; ; ; ; ;
2018
Soc.
Washington, DC
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Please use a persistent id in citations: doi:10.1021/acs.macromol.8b00096
Abstract: Based on diblock copolymers, a pair of “schizo-phrenic” micellar systems is designed by combining a nonionic andthermoresponsive block with a zwitterionic block, which isthermoresponsive and salt-sensitive. The nonionic block ispoly(N-isopropylacrylamide) (PNIPAM) or poly(N-isopropyl-methacrylamide) (PNIPMAM) and exhibits a lower criticalsolution temperature (LCST) behavior in aqueous solution. Thezwitterionic block is a polysulfobetaine, i.e., poly(4-((3-methacryl-amidopropyl)dimethylammonio)butane-1-sulfonate) (PSBP), andhas an upper critical solution temperature (UCST) behavior withthe clearing point decreasing with increasing salt concentration. The PSBP-b-PNIPAM and PSBP-b-PNIPMAM diblockcopolymers are prepared by successive reversible addition−fragmentation chain transfer (RAFT) polymerizations. The PSBPblock is chosen such that the clearing point of the homopolymer is significantly higher in pure water than the cloud point ofPNIPAM or PNIPMAM. Using turbidimetry, 1H NMR, and small-angle neutron scattering, we investigate the overall phasebehavior as well as the structure and interaction between the micelles and the intermediate phase, both in salt-free D2O and in0.004 M NaBr in D2O in a wide temperature range. We find that PSBP-b-PNIPAM at 50 g L−1 in salt-free D2O is turbid in theentire temperature range. It forms spherical micelles below the cloud point of PNIPAM and cylindrical micelles above. Similarbehavior is observed for PSBP-b-PNIPMAM at 50 g L−1 in salt-free D2O with a slight and smooth increase of the lighttransmission below the cloud point of PNIPMAM and an abrupt decrease above. Upon addition of 0.004 M NaBr, the UCST-type cloud point of the PSBP-block is notably decreased, and an intermediate regime is encountered below the cloud point ofPNIPMAM, where the light transmission is slightly enhanced. In this regime, the polymer solution exhibits behavior typical forpolyelectrolyte solutions. Thus, double thermosensitive and salt-sensitive behavior with “schizophrenic” micelle formation isfound, and the width of the intermediate regime, where both blocks are hydrophilic, can be tuned by the addition of electrolyte.
Keyword(s): Polymers, Soft Nano Particles and Proteins (1st) ; Chemistry (2nd)
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