la9b00241_si_001.pdf (1.14 MB)
All-In-One “Schizophrenic” Self-Assembly of Orthogonally Tuned Thermoresponsive Diblock Copolymers
journal contribution
posted on 2019-04-24, 00:00 authored by Natalya
S. Vishnevetskaya, Viet Hildebrand, Noverra M. Nizardo, Chia-Hsin Ko, Zhenyu Di, Aurel Radulescu, Lester C. Barnsley, Peter Müller-Buschbaum, André Laschewsky, Christine M. PapadakisSmart,
fully orthogonal switching was realized in a highly biocompatible
diblock copolymer system with variable trigger-induced aqueous self-assembly.
The polymers are composed of nonionic and zwitterionic blocks featuring
lower and upper critical solution temperatures (LCSTs and UCSTs).
In the system investigated, diblock copolymers from poly(N-isopropyl methacrylamide) (PNIPMAM) and a poly(sulfobetaine methacrylamide),
systematic variation of the molar mass of the latter block allowed
for shifting the UCST of the latter above the LCST of the PNIPMAM
block in a salt-free condition. Thus, successive thermal switching
results in “schizophrenic” micellization, in which the
roles of the hydrophobic core block and the hydrophilic shell block
are interchanged depending on the temperature. Furthermore, by virtue
of the strong electrolyte-sensitivity of the zwitterionic polysulfobetaine
block, we succeeded to shift its UCST below the LCST of the PNIPMAM
block by adding small amounts of an electrolyte, thus inverting the
pathway of switching. This superimposed orthogonal switching by electrolyte
addition enabled us to control the switching scenarios between the
two types of micelles (i) via an insoluble state, if the LCST-type
cloud point is below the UCST-type cloud point, which is the case
at low salt concentrations or (ii) via a molecularly dissolved state,
if the LCST-type cloud point is above the UCST-type cloud point, which
is the case at high salt concentrations. Systematic variation of the
block lengths allowed for verifying the anticipated behavior and identifying
the molecular architecture needed. The versatile and tunable self-assembly
offers manifold opportunities, for example, for smart emulsifiers
or for sophisticated carrier systems.