Characterization of Diblock Copolymer Order-Order Transitions in Semidilute Aqueous Solution Using Fluorescence Correlation Spectroscopy

Abstract

gels at relatively high concentrations. [ 1,2 ] Judicious choice of the copolymer allows the design of hydrogels that are responsive to temperature [ 3,4 ] or pH. [5][6][7][8] However, it is relatively unusual for such a copolymer to respond to both temperature and pH.In principle, biocompatible block copolymer gels can be used as a long-term cell storage medium. [ 9 ] One promising candidate for such applications is a diblock copolymer comprising poly(glycerol monomethacrylate) (PGMA) and poly(2-hydroxypropyl methacrylate) (PHPMA), which are conveniently prepared via polymerization-induced self-assembly [9][10][11][12][13] using reversible addition-fragmentation chain transfer (RAFT) aqueous dispersion polymerization. [14][15][16] This versatile approach has enabled spherical, worm-like or vesicular copolymer morphologies to be generated in concentrated solution. [ 11,[17][18][19][20][21][22][23][24][25][26] Such a nonionic PGMA-PHPMA diblock copolymer exhibits a thermoreversibleThe temperature and pH-dependent diffusion of poly(glycerol monomethacrylate)-blockpoly(2-hydroxypropyl methacrylate) nanoparticles prepared via polymerization-induced self-assembly in water is characterized using fl uorescence correlation spectroscopy (FCS). Lowering the solution temperature or raising the solution pH induces a worm-to-sphere transition and hence an increase in diffusion coeffi cient by a factor of between four and eight. FCS enables morphological transitions to be monitored at relatively high copolymer concentrations (10% w/w) compared to those required for dynamic light scattering (0.1% w/w). This is important because such transitions are reversible at the former concentration, whereas they are irreversible at the latter. Furthermore, the FCS data suggest that the thermal transition takes place over a very narrow temperature range (less than 2 °C). These results demon strate the application of FCS to characterize orderorder transitions, as opposed to order-disorder transitions.

Stimulus‐Responsive Nanoparticles and Associated (Reversible) Polymorphism via Polymerization Induced Self‐assembly (PISA)

“…For example, Armes and co‐workers recently reported such dual‐responsive non‐ionic HOOC‐p(GMA x ‐ b ‐HPMA y ) diblock copolymer worm gels exhibiting an interesting reversible W‐to‐S transition with concomitant degelation process upon switching the solution pH or the temperature . Similarly, the thermo‐ and pH‐triggered irreversible V‐to‐W and V‐to‐S transition of p(GMA x ‐ b ‐HPMA y ) nano‐aggregates was described .…”

“…In this and subsequent studies, the p(GMA x ‐ b ‐HPMA y ) system and its thermoresponsiveness were investigated in detail including through electron microscopy, dynamic light scattering, variable temperature 1 H NMR measurements, SAXS, rheology, and fluorescence correlation spectroscopy . Free‐standing gels could be reconstituted after freeze‐drying by re‐dissolving in water at 3–5 °C prior to heating to room temperature .…”

“…In this and subsequent studies, the p(GMA x -b-HPMA y ) system and its thermoresponsiveness were investigated in detail including through electron microscopy, dynamic light scattering, variable temperature 1 H NMR measurements, SAXS, [74] rheology, [42] and fluorescence correlation spectroscopy. [75] Free-standing gels could be reconstituted after freeze-drying by re-dissolving in water at 3-5 °C prior to heating to room temperature. [76] The (de)gelation temperature of p(GMA x -b-HPMA y ), below room temperature in the above cases, could be increased to 31 °C by the incorporation of 30 mol-% of hydrophilic di(ethylene glycol) methyl ether methacrylate (DEGMA) co-monomers into the core-forming block.…”

“…For example, Armes and co-workers recently reported such dual-responsive non-ionic HOOC-p(GMA x -b-HPMA y ) diblock copolymer worm gels exhibiting an interesting reversible W-to-S transition with concomitant degelation process upon switching the solution pH or the temperature. [74,75,103] Similarly, the thermo-and pH-triggered irreversible V-to-W and V-to-S transition of p(GMA x -b-HPMA y ) nanoaggregates was described. [108] When compared with the W-to-S transition, however, transitions from a vesicular phase to worm or sphere phase were significantly slower, with a longer response time (hours), which is probably due to a significant kinetic barrier associated with vesicletype structures.…”

One‐Pot Synthesis of Double Poly(Ionic Liquid) Block Copolymers by Cobalt‐Mediated Radical Polymerization‐Induced Self‐Assembly (CMR‐PISA) in Water

“…[ 31 ] The direct synthesis of amphiphilic block copolymers in water has gained an increasing interest in the last years with the development of the so-called polymerization induced self-assembly (PISA) process. [ 22,[32][33][34][35][36][37][38] When carried out in aqueous media, PISA involves the synthesis of a hydrophilic polymer precursor in water, prior to its use as a macroinitiator (or macrochain transfer agent) for the polymerization of a monomer that provides the hydrophobic block. The so-formed amphiphilic AB diblock copolymer self-assembles in water into nanoobjects, whose size and structure depend on the selected macromolecular parameters.…”