Temperature-Responsive Nanospheres with Bicontinuous Internal Structures from a Semicrystalline Amphiphilic Block Copolymer

Abstract

Internally structured self-assembled nanospheres, cubosomes, are formed from a semi-crystalline block copolymer, poly(ethylene oxide)-block-poly(octadecyl methacrylate) (PEO39-b-PODMA17), in aqueous dispersion. The poly(octadecyl methacrylate) block provides them with a temperature responsive structure and morphology. Using cryo-electron tomography, we show that at room temperature these internally bicontinuous aggregates undergo an unprecedented order-disorder transition of the microphase separated domains that is accompanied by a change in the overall aggregate morphology. This allows switching between spheres with ordered bicontinuous internal structures at temperatures below the transition temperature and more planar oblate spheroids with a disordered microphase-separated state above the transition temperature. The bicontinuous structures offer a number of possibilities for application as templates e.g. for biomimetic mineralisation or polymerization. Furthermore, the unique nature of the thermal transition observed for this system offers up considerable possibilities for their application as temperature-controlled release vessels. Amphiphilic AB and ABA block copolymers have been demonstrated to form a variety of self-assembled aggregate structures in dilute solutions where the solvent preferentially solvates one of the blocks. Temperature responsive nanospheres with bicontinuous internal structures from a semi-crystalline amphiphilic block copolymer1 The most common structures formed by these amphiphilic macromolecules are spherical micelles, cylindrical micelles and vesicles (polymersomes), with the type of aggregate depending principally upon the relative volumes of the different blocks.1 Over the past decade more complex aggregate structures have been observed and targeted for construction. The majority of these aggregates (such as disk-like and toroidal micelles) may be grouped under the description of complex micelles and can be achieved both through manipulating block copolymer structures and through physical means.2 Multicompartment micelles are typically the result of ABC block copolymers, of which one of the blocks is solvophilic and the remaining two are solvophobic but do not mix.3 Hence microphase separated micellar cores result.We recently reported the experimental observation of complex micelles with bicontinuous hydrophilic/hydrophobic internal structures from amphiphilic norbornene-based double-comb diblock copolymers, with peptide and oligo(ethylene oxide) side chain.4 Block copolymer nanoparticles with similar bicontinuous phase separation have also been observed by Wooley et al, 5 and before that were predicted by Fraaije and Sevink. 6 In the present paper we demonstrate the formation of similar complex micelles, with hydrophobic bicontinuous internal morphologies from an amphiphilic semi-crystalline AB(C) comb-like block copolymer. Using cryo-electron tomography, we show that at room temperature these internally structured nanoparticles undergo an unprecedented order-disorder transiti...

Controlling supramolecular polymerization through multicomponent self‐assembly

“…These were dissolved in an alkane solvent (e.g., hexane) which lead to the formation of rod-like micelles, driven by the formation of a hexane insoluble PFS core and a hexane swollen PI or PDMS corona. While the majority of block copolymer based morphologies described in the literature are formed under conditions close to thermodynamic control and subsequently trapped in kinetically frozen states, [60][61][62][63][64][65][66][67][68][69][70][71][72][73] Winnik and Manners were able to exploit the crystalline nature of PFS in order to manipulate the growth into one-dimensional micelles of controlled length and architecture. 31 By heating the hexane solution of block copolymers to 60 8C, free unimer chains were obtained that upon slow cooling produce a discrete number of nuclei, a process described as the nucleation phase.…”

“…Strategies to control the size and shape of nano-and micrometer size objects that rely on selective solvent techniques in the self-assembly of block copolymers will not be discussed here. [60][61][62][63][64][65][66][67][68][69][70][71][72][73] Supramolecular multicomponent gels, [74][75][76][77][78][79][80][81][82][83][84][85][86][87][88][89] or orthogonal self-assembly, [90][91][92][93][94][95][96][97] self-sorting [98][99][100][101][102][103][104] and chiral amplification strategies 105 in multicomponent supramolecular polymers will not be covered in detail, and the interested reader is referred to the recent literature and review articles.…”

Biomimetic synthesis of calcium carbonate bilayers interfaced by a diblock copolymer template

“…Similarly one can envision the use of the selfassembled bicontinous block polymer templates for controlled formation of complex mineral morphologies. Such complex block copolymer micelles with a bicontinuous interior were recently demonstrated for a poly-octadecyl methacrylate (PODMA)-based block copolymer [53]. Mineralization of their interior and subsequent chemical conversion of the hydrophobic (PODMA) blocks to hydrophilic PAA blocks would provide the space and the templating capability required for the deposition of a second mineral phase inside the first one.…”

Controlling the melting transition of semi-crystalline self-assembled block copolymer aggregates: controlling release rates of ibuprofen

“…4,5 We have previously reported on the thermo-responsive nature of bicontinuous polymer nanospheres (BPNs) that selfassembled in aqueous dispersions from PEO-b-PODMA. 6 BPNs are discrete aggregates that have a twisted hydrophobic network interconnected with that of a hydrophobic moiety. The self-assembly of BPNs from PEO-b-PODMA has been investigated previously by Holder and Sommerdijk et al and it was found that the weight fraction of the hydrophilic block (PEO) should be between 15-25% with the molecular weight at < 17 kDa for BPNs to form.…”