A Morphological Transition of Inverse Mesophases of a Branched‐Linear Block Copolymer Guided by Using Cosolvents

Abstract

We report here as trategy for influencing the phase and lattice of the inverse mesophases of as ingle branchedlinear block copolymer (BCP) in solution which does not require changing the structure of the BCP.T he phase of the self-assembled structures of the blockc opolymer can be controlled ranging from bilayer structures of positive curvature (polymersomes) to inverse mesophases (triply periodic minimal surfaces and inverse hexagonal structures) by adjusting the solvent used for self-assembly.B yu sing solvent mixtures to dissolve the blockc opolymer we were able to systematically change the affinity of the solvent towardthe polystyrene block, which resulted in the formation of inverse mesophases with the desired lattice by self-assembly of as ingle branched-linear blockc opolymer.O ur method was also applied to an ew solution self-assembly method for ab ranched-linear block copolymer on as tationary substrate under humidity,w hich resulted in the formation of large mesoporous films.O ur results constitute the first controlled transition of the inverse mesophases of blockc opolymers by adjusting the solvent composition.The direct self-assembly of amphiphilic block copolymers (BCPs) into inverse bicontinuous structures in solution is an emerging strategy for creating highly ordered porous polymers with three-dimensionally interconnected networks of large pores. [1][2][3][4][5][6][7][8][9] In am anner similar to the self-assembly of lipids such as monoolein into colloidal particles of inverse bicontinuous cubic mesophases (cubosomes) in water, [10][11][12][13][14][15] BCPs in solution could be directly self-assembled into colloidal particles of inverse bicontinuous cubic phases of the BCP bilayer (polymer cubosomes). [1][2][3][4][5][6][7][16][17][18][19] We recently reported that diblock copolymers,composed of adendritic or branched hydrophilic block and ahydrophobic linear polymer block, preferentially self-assemble into triply periodic minimal surfaces (TPMSs) of the BCP bilayers in solution, resulting in the creation of polymer cubosomes having highly defined internal large-pore networks. [16][17][18] The TPMSs of the BCP bilayers exhibited distinct crystalline structures such as primitive cubic (Im3m,Psurface), double diamond (Pn3m,Dsurface), and gyroid (Ia3d,Gsurface) lattices,d epending on the architecture of the dendritic hydrophilic block as well as the block ratio between two distinct polymer domains.T he polymer cubosomes of these BCPs exhibited al arge surface area, which could be functionalized by implementing the desired functional groups through co-assembly with linear BCPs with a-functionalized hydrophilic blocks.M oreover,t he TPMSs of the BCP bilayer could be expanded to large-scale films by the diffusion of water under saturated humidity into ac oncentrated solution of BCP cast on as tationary substrate. [18] Our previous studies suggested that the branched architecture of the hydrophilic block played ac rucial role in the preferential self-assembly of branched-linear BCPs (Scheme 1) i...

Structural Requirements of Block Copolymers for Self-Assembly into Inverse Bicontinuous Cubic Mesophases in Solution

“…When this value was greater than 1, the formation of IBC and inverse hexagonal phases in solution was preferential. 29,30 In contrast to the formation of identical inverse mesophases from the self-assembly of branched−linear BCPs with the same PEG750 3 hydrophilic block, bb-BCPs having the branched hydrophobic blocks exhibited the formation of IBC mesophases at significantly higher f PEG values ( Figure 3). For example, the f PEG values of PEG750 3 -PS n that showed preferential selfassembly into IBC mesophases ranged from 5.4 to 5.7%.…”

“…29 We inferred that the increased molecular area might force the hydrophobic chain to be less stretched to have a reduced dimension upon the formation of bilayers. 29,30 To support this assumption, we previously synthesized BCPs having branched architectures in both polymer blocks. 29 The BCPs having a branched PS block showed a strong tendency to form inverse mesophases in dilute solution, suggesting that the dimension of the hydrophobic block at the given molecular weight could critically influence the self-assembly behavior of the BCP in solution.…”

An Overview of Materials with Triply Periodic Minimal Surfaces and Related Geometry: From Biological Structures to Self‐Assembled Systems

“…Kim and co‐workers synthesized a series of branched block copolymers and investigated the effect of the architecture of the block copolymers on their solution self‐assembly into inverse mesophases . The precise control of the molecular shape from dendritic–linear to branched–linear to branched–branched by adjusting the solvent leads to the effective tuning of the molecular packing parameter and drives the block copolymer self‐assembly into vesicle, lamellar, inverse bicontinuous P and D cubic mesophases, and inverse hexagonal phases.…”

“…The precise control of the molecular shape from dendritic–linear to branched–linear to branched–branched by adjusting the solvent leads to the effective tuning of the molecular packing parameter and drives the block copolymer self‐assembly into vesicle, lamellar, inverse bicontinuous P and D cubic mesophases, and inverse hexagonal phases. It has been suggested that the branched shape of block copolymers plays an important role in the preferential self‐assembly into the D and P surface structures by affecting the chain dimensions of the hydrophobic block with respect to the bilayer plane . Very recently, Lin et al revealed that porous cubosomes with inverse P and D mesophases as well as hexasomes with inverse hexagonal structures can also be formed from simple block copolymers, such as PS‐ b ‐PEO.…”

Head–Tail Asymmetry as the Determining Factor in the Formation of Polymer Cubosomes or Hexasomes in a Rod–Coil Amphiphilic Block Copolymer

“…Because the PEO block has the same MW in the ABCPs, the increase in the head-tail asymmetry caused by increasing PMPCS length or initial polymer concentration will lead to alarger P. Therefore,aphase transition from the flat lamellar structure and spongy structure to the polymer cubosome and hexasome occurs.T oinvestigate the applicability of the headtail asymmetry argument, different proportions of N,Ndimethylformamide (DMF, d DMF = 24.7 MPa À1/2 )w ere mixed with THF (d THF = 18.6 MPa À1/2 )t oi ncrease the affinity between the mixed solvent and PMPCS (d PMPCS % 22 MPa À1/ 2 ), [14] changing the head-tail asymmetry because of the increase in the volume and chain dimension of the semirigid PMPCS.T he sample E 45 M 38 with mostly as pongy structure (Figure 4a)i nT HF/H 2 Ow as used. Thed etailed self-assembling process is described in the Supporting Information, and the initial concentration in such astudy is fixed at 1wt%.Whenthe DMF content is increased to 5wt%,E 45 M 38 self-assembles into an Im3 m polymer cubosome (Figure 4b; Supporting Information, Figure S11a).…”