ma8b00096_si_001.pdf (812.56 kB)
Dual Orthogonal Switching of the “Schizophrenic” Self-Assembly of Diblock Copolymers
journal contribution
posted on 2018-03-23, 18:20 authored by Natalya
S. Vishnevetskaya, Viet Hildebrand, Margarita A. Dyakonova, Bart-Jan Niebuur, Konstantinos Kyriakos, Konstantinos N. Raftopoulos, Zhenyu Di, Peter Müller-Buschbaum, André Laschewsky, Christine M. PapadakisBased on diblock copolymers, a pair
of “schizophrenic”
micellar systems is designed by combining a nonionic and thermoresponsive
block with a zwitterionic block, which is thermoresponsive and salt-sensitive.
The nonionic block is poly(N-isopropylacrylamide)
(PNIPAM) or poly(N-isopropylmethacrylamide)
(PNIPMAM) and exhibits a lower critical solution temperature (LCST)
behavior in aqueous solution. The zwitterionic block is a polysulfobetaine,
i.e., poly(4-((3-methacrylamidopropyl)dimethylammonio)butane-1-sulfonate)
(PSBP), and has an upper critical solution temperature (UCST) behavior
with the clearing point decreasing with increasing salt concentration.
The PSBP-b-PNIPAM and PSBP-b-PNIPMAM
diblock copolymers are prepared by successive reversible addition–fragmentation
chain transfer (RAFT) polymerizations. The PSBP block is chosen such
that the clearing point of the homopolymer is significantly higher
in pure water than the cloud point of PNIPAM or PNIPMAM. Using turbidimetry, 1H NMR, and small-angle neutron scattering, we investigate
the overall phase behavior as well as the structure and interaction
between the micelles and the intermediate phase, both in salt-free
D2O and in 0.004 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 the entire temperature
range. It forms spherical micelles below the cloud point of PNIPAM
and cylindrical micelles above. Similar behavior is observed for PSBP-b-PNIPMAM at 50 g L–1 in salt-free D2O with a slight and smooth increase of the light transmission
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 of PNIPMAM, where the light transmission is slightly
enhanced. In this regime, the polymer solution exhibits behavior typical
for polyelectrolyte solutions. Thus, double thermosensitive and salt-sensitive
behavior with “schizophrenic” micelle formation is found,
and the width of the intermediate regime, where both blocks are hydrophilic,
can be tuned by the addition of electrolyte.