Formation and Reversible Morphological Transition of Bicontinuous Nanospheres and Toroidal Micelles by the Self‐Assembly of a Crystalline‐b‐Coil Diblock Copolymer

Abstract

We herein report the formation of two complex nanostructures,t oroidal micelles and bicontinuous nanospheres,b yt he self-assembly of the single structurally simple crystalline-b-coil diblock copolymer poly[bis(trifluoroethoxy)phosphazene]-b-poly(styrene), PTFEP-b-PS,i n one solvent (THF) and without additives.T he nature of these nanostructures in solution was confirmed by DLS and cryo-TEM experiments.The two morphologies are related by means of anew type of reversible morphological evolution, bicontinuous-to-toroidal, triggered by changes in the polymer concentration. WAXS experiments showed that the degree of crystallinity of the PTFEP chains located at the core of the toroids was higher than that in the bicontinuous nanospheres,t hus indicating that the final morphology of the aggregates is mostly determined by the ordering of the PTFEP core-forming blocks.The self-assembly of amphiphilic block copolymers (BCPs) has been demonstrated as an invaluable tool for the construction of well-defined nanostructures. [1] Besides the classical nanomorphologies created by this methodology (spheres,c ylinders,o rb ilayer membranes), [1,2] nanotoroids (donut-or ring-shaped) and bicontinuous nanospheres have become textures of special interest owing to their rarity, complexity,a nd importance in some technological and biological processes.F or instance,N ature uses nanotoroidal morphologies during DNApackaging (DNAcondensation) [3] and in some viruses and sperm cells. [4] Toroids are also very important in the design of artificial delivery systems for gene therapy. [5] On the other hand, micelles with internal bicontinuous structures are considered promising carriers for the simultaneous inclusion of chemically different encapsulated drugs and of interest for their possible catalytic and templating properties. [6] Since pioneering studies on the synthesis of toroidal [7] and bicontinuous nanostructures [8] from the selfassembly of BCPs,very few examples of toroidal (mixed with other morphologies) [9] and bicontinuous [10] micelles derived from BCPs have been reported, mostly from chemically and structurally rather complex combinations of blocks.However, these two morphologies have also been produced purely from simple linear block copolymers, [11] thus demonstrating that structural complexity is not an ecessary condition for their formation.Theself-assembly of block copolymers containing ac rystallizable core-forming block and ar andom-coil block (crystalline-b-coil BCPs) has been exploited to create complex nanomorphologies by crystallization-driven living self-assembly. [12] Recently,our group has demonstrated the synthesis of reversibly responsive (to changes in pH) giant unilamellar vesicles (GUVs) by the self-assembly of the BCPs [N = P(OCH 2 CF 3 ) 2 ] n -b-[N = PMePh] m containing crystalline [N=P(OCH 2 CF 3 ) 2 ]s egments. [13] Herein we report an ew and convenient synthesis of the hybrid crystalline-b-coil poly-[bis(trifluoroethoxy)phosphazene]-b-polystyrene (PTFEP-PS) by the use of lithiated initiators funct...

Degradable, Dendritic Polyols on a Branched Polyphosphazene Backbone

“…First, a poly­(dichloro)­phosphazene [NPCl 2 ] n tri-arm star was synthesized via the recently developed core first, room temperature, living cationic polymerization of trichlorophosphoranimine (Cl 3 PNSi­(CH 3 ) 3 starting from 1,1,1-tris­(diphenylphosphino)­methane chlorinated with C 2 Cl 6 , (Scheme ). A postpolymerization substitution reaction was conducted with an excess of propargylamine to give the alkyne-substituted star polymer 1 with on average seven repeat units per arm (calculated by 1 H NMR end group analysis).…”

Self-Assembly of Oligo- and Polypeptide-Based Amphiphiles: Recent Advances and Future Possibilities

“…In related studies, Lin and co-workers also observed supramolecular polymerization 20 of similar rodlike micelles formed by poly(benzyl-L-glutamate-g-PEG) and studied the supramolecular polymerization kinetics. 21 In the formation of toroids, there is often competition between the coalescence of the highly curved ends of the rodlike micelle into a toroidal morphology and the ends of two rods connecting to form a supramolecular polymer; 22 thus, studying the kinetics of supramolecular polymerization and energetic factors that dictate toroid formation will be critical for scientists to target one morphology over the other.…”