Coil Block Copolymers Research Articles

Combining Two Powerful Living Polymerizations Using Rationally Designed Bifunctional Initiators for Versatile Synthesis of Conjugated Rod–Coil Block Copolymers

Combining Two Powerful Living Polymerizations Using Rationally Designed Bifunctional Initiators for Versatile Synthesis of Conjugated Rod–Coil Block Copolymers

Tuning Cocrystallization, Microphase Separation, and Optical Property of All-Conjugated Triblock Copolymers by Molecular Engineering

Compared to the widely studied classical coil–coil block copolymers (BCPs) with well-established phase diagram and recent advances achieved in all-conjugated diblock copolymers, the investigation into the phase behavior of all-conjugated triblock copolymers is rather limited. In this work, we prepare a series of triblock copolymers containing various poly(3-alkylthiophene)s (P3ATs), interrogate their phase transition between cocrystallization and microphase separation adjusted by a set of molecular parameters (alkyl side chains, block ratios, and block sequences), and correlate these different structures strongly to their optical properties. Poly(3-butylthiophene) (P3BT), poly(3-hexylthiophene) (P3HT), poly(3-(2′-ethyl)hexylthiophene) (P3EHT), poly(3-octylthiophene) (P3OT), and poly(3-dodecylthiophene) (P3DDT) are selected, in which P3EHT has a much less crystalline capability than the other four components. Interestingly, when the P3EHT block is situated in the BCP middle position (P3BT-b-P3EHT-b-P3AT), a smaller side chain difference between the two outer P3BT and P3AT blocks and the P3EHT with a shorter main chain length favor cocrystallization in the triblock copolymers over microphase separation. Moreover, when changing the block sequence to place the P3EHT block at two terminals (P3OT-b-P3BT-b-P3EHT and P3BT-b-P3OT-b-P3EHT), they display stronger cocrystalline capability than P3BT-b-P3EHT-b-P3OT with the P3EHT in the central. At last, these various crystalline structures are related to their optical properties. This work demonstrates the tuning of the phase transition between cocrystalline and microphase-separated structures in conjugated triblock copolymers via molecular engineering, which correlate closely to their optical properties and may underpin their applications in optoelectronic devices.

Synthesis and self-assembly of fluorinated supramolecular mesogen-jacketed liquid crystalline polymer and its high-χ block copolymer constructed by hydrogen bonding

By connecting a fluorinated molecule 2,5-bis((4-(perfluorohexyl)benzoyl)oxy)benzoic acid (6DFP) to the poly(4-vinylpyridine) (P4VP) backbone through hydrogen bonding, we synthesized a new series of fluorinated supramolecular mesogen-jacketed liquid crystalline polymer (MJLCP) P4VP(6DFP)x, where x is the molar ratio of donor to acceptor. Polarized light microscopy and wide-angle X-ray scattering were used to investigate the liquid crystallinity of the resulting complexes. The results show that this kind of supramolecular MJLCP has good thermal stability, with the isotropization temperature of about 170 °C. Subsequently, by connecting the fluorinated molecule 6DFP to the commercially available coil−coil block copolymer (BCP) polystyrene-block-poly(4-vinylpyridine) (PS-b-P4VP) chain also via hydrogen bond, we constructed a series of supramolecular rod−coil BCP PSmVn(6DFP)x, where m and n are the degrees of polymerization of PS and P4VP, respectively. PSmVn(6DFP)x exhibits a hierarchically ordered self-assembled structure. Owing to the introduction of fluorine atoms, the Flory-Huggins interaction parameter (χ) of such a supramolecular BCP is high. BCP sample with a low total degree of polymerization can still be ordered, and the periodic size can be as low as 11.5 nm. This work provides a new approach for the construction of small-sized structures by supramolecular BCPs via hydrogen bonding, which can be used as nanotemplates and nanoporous materials after selective removal of the small molecules.

2D Liquid-Crystallization-Driven Self-Assembly of Rod-Coil Block Copolymers: Living Growth and Self-Similarity.

Liquid-crystallization-driven self-assembly (LCDSA) is an emerging methodology, which has been employed to construct controllable 1D nanostructures. However, 2D nanostructures via living LCDSA are rarely reported, and the complicated growth kinetics are not well-known. Herein, we perform Brownian dynamics (BD) simulations to investigate the 2D living growth of disklike micelles via LCDSA of rod-coil block copolymers. The 2D seeded-growth behavior is achieved by incorporating the unimers onto the edges of disklike seeds with smectic-like liquid-crystalline (LC) cores. The fluidity of such LC-like micellar cores is conducive to the chain adjustments of rod blocks during the 2D living growth process. The apparent growth rate and unique self-similarity kinetics are governed by the interplay between the variations in the growth rate coefficient and the reactive sites at the micelle edges. This work provides an in-depth understanding of the 2D living growth of micelles and guidance to construct well-defined 2D hierarchical nanostructures.

Polymer Vesicles in a Nanochannel under Flow Fields: A DPD Simulation Study

AbstractThe general lack of knowledge on the dynamics of polymer vesicles under flow field has confounded their applications in drug delivery and other fields. Therefore, dissipative particle dynamics (DPD) simulations on the dynamic behavior of diblock copolymer vesicles in a nanochannel under Poiseuille flow are conducted. The simulation results show that the block copolymer vesicles with hydrophobic blocks of different rigidities exhibit significantly different mechanical stabilities under the flow fields. With increasing the Reynolds number, the coil–coil block copolymer vesicles undergo a shape transition from spherical to bullet‐like to asymmetric and eventually split into two parts. In contrast, the rod–coil block copolymer vesicles deform from spherical to bullet‐like to parachute‐like structures and ultimately ruptured. The flow‐induced distortion and reorganization of copolymers mainly cause the deformation of vesicles. The distinguished motions of the block copolymers with different rigid blocks lead to the distinct performance of the vesicles. The findings could help understand the flow behavior of polymer vesicles in a nanochannel or a blood vessel and assist the design of bio‐functional polymersomes.

A Unique Nano‐Capsule Possessing Inner Thermo‐Responsive Surface Prepared from a Toothbrush‐Like Comb−Coil Block Copolymer

Front Cover: In article number 2100174 by Haruka Takebuchi and Ren-Hua Jin, a double hydrophilic coil-brush block copolymer self-asssembles into core-corona micelles in water under heating. Via cross-linking the corona, the micelle is transformed into a nanocapsule which has an inner thermo-responsive surface. When heating step-by-step in a wide range of temperatures, the nanocapsule shrinks gradually, while when cooling step-by-step, the nanocapsule swells gradually back to its original size.

A Unique Nano‐Capsule Possessing Inner Thermo‐Responsive Surface Prepared from a Toothbrush‐Like Comb−Coil Block Copolymer

AbstractPoly(N‐isopropylacrylamide) (PNIPAM) having lower critical solution temperature (LCST) behavior in aqueous solutions has been actively studied for various applications in nanotechnology and controlled drug delivery. In this work, a comb‐coil block copolymer is synthesized with PNIPAM coil and polyethyleneimine brushes. Self‐organization of the copolymer into micelle by heating and subsequent cross‐linking of the part of PEI corona resulted in a unique nanocapsule (i‐CLM) with hydrophilic cross‐linked PEI outer shell and thermo‐responsive PNIPAM inner brush. The nanocapsule appears as a vesicle‐like hollow at room temperature but did into micelle‐like spheres when heated. From dynamic light scattering measurement, it is revealed apparently that the nanocapsule exhibited well the swelling and the shrinking reversibly under heating and cooling and the feature is cycled repeatedly with gradual fashion under wide‐range of temperature responding. The carrier property of the nanocapsule is investigated by using hydrophobic fluorophore of Nile red (NR) as a probe and it is found that the hollow of the nanocapsule is a good nano pocket to promote the growth of nanocrystals of NR.

Achieving Superior Energy Storage Properties of All-Organic Dielectric Polystyrene-Based Composites by Blending Rod–Coil Block Copolymers

With the excessive consumption of natural resources and the miniaturization trends of advanced electronic products and equipment, there is an urgent need to improve the energy density and efficiency of polymeric dielectrics. In this paper, we explore the effect of rod–coil block copolymer polystyrene-b-poly[bis(4-cyanophenyl) 2-vinylterephthalate] (denoted as PS-b-PBCN) on the dielectric behavior and energy storage properties of PS-based blend films. The dipolar glass rigid polymer PBCN can have a columnar nematic phase, a high glass-transition temperature of 156 °C, a high relative permittivity (εr) of 14, and a low band gap of ≈3.44 eV; however, it has poor film-forming properties. Linear dielectric PS possesses low cost, and good film-forming and insulation properties, with a low εr value of 2.5. Two types of PS-b-PBCN block copolymers (PS158-b-PBCN78 and PS158-b-PBCN16), including a coil PS block and an electronically polarized rod PBCN block, are fabricated via reversible addition–fragmentation chain transfer polymerization polymerization. The PBCN/PS- and PS-b-PBCN/PS-blended films are synthesized by solution casting. The experimental results indicate that the εr and breakdown strength of the blend films improve with an increasing mass content of homopolymer PBCN or block copolymer PS-b-PBCN. A maximum εr value of 5.8 at 1 kHz is obtained in the 30 wt % PS158-b-PBCN78/PS blend film owing to the good compatibility and high loading of the polar polymer PBCN. Moreover, a low dielectric loss of 0.018 is found. A discharged energy density of 2.16 J/cm3 with a high efficiency of 90% at 295 MV/m is achieved because PBCN can immobilize free electrons and restrict the long-distance migration of charges. This work provides an idea for the fabrication of all-organic PS-based dielectrics with a high energy storage performance by introducing rod–coil block copolymers.

Annealing Process Dependence of the Self-Assembly of Rod–Coil Block Copolymer Thin Films

Thermal annealing, solvent vapor annealing, and a two-step solvent plus thermal annealing are applied to a series of silicon-containing rod–coil thermotropic liquid crystalline (LC) block copolymer thin films with LC volume fractions of 0.42–0.85. Solvent vapor annealing using selective solvents of acetone and heptane produced a wide range of ordered nanostructures with small feature sizes, such as sub-10 nm cylinders, gyroids, and spheres. Subsequent thermal annealing yields final morphologies that depend on the initial morphology and the thermotropic LC phase transition. Combined thermal and solvent annealing as well as design of the rod and coil volume fractions provides an effective way to control the morphologies of rod–coil block copolymers.

Microphase separation in helix-coil block copolymer melts: computer simulation.

By means of molecular dynamics simulation, the process of the microphase separation in the melts of diblock helix-coil copolymers comprising a flexible and a helical block was studied. The resulting microstructures were examined, and the spatial distribution of the blocks and molecular packing were investigated. The phase diagram was built in terms of the fraction of the helical block and the incompatibility parameter of the blocks. The comparison of the diagrams for helix-coil and the classic coil-coil copolymer blends was carried out. It was shown that the total region where the ordering into distinctive microstructures takes place is similar for both diagrams. But for the helix-coil copolymers the area of the cylinders splits into the region of those with circular and elliptical cross-sections; the bicontinuous phase area is much wider; in the lamellar phases, the helical blocks were oriented precisely perpendicular to the lamellar interface, forming a cohesive interlocked structure of densely packed helices.

Unravelling the Correlation between Microphase Separation and Cocrystallization in Thiophene-Selenophene Block Copolymers for Organic Field-Effect Transistors

Despite significant advances in double-crystalline coil–coil block copolymers (BCPs), investigations into double-crystalline all-conjugated rod–rod BCPs have been comparatively fewer and are limite...

Synthesis of Conjugated Rod–Coil Block Copolymers by RuPhos Pd-Catalyzed Suzuki–Miyaura Catalyst-Transfer Polycondensation: Initiation from Coil-Type Polymers

A novel coil-first/grafting-from approach was developed for the synthesis of conjugated rod–coil block copolymers using RuPhos Pd-catalyzed Suzuki–Miyaura catalyst-transfer polycondensation (SCTP). First, aryl iodide end-functionalized polystyrene (PS) was prepared as a macroinitiator for SCTP via atom transfer radical polymerization (ATRP) followed by sequential end-group modifications, azidation, and click reactions. Then, RuPhos Pd-catalyzed SCTP using the PS macroinitiator was carried out in the presence of N-methyliminodiacetic acid boronate-containing 3-hexylthiophene monomer (M1), and this afforded well-defined PS-block-poly(3-hexylthiophene) with excellent control and high yield. The scope of this method was successfully expanded to include poly(methyl acrylate)-, poly(methyl methacrylate)-, and poly(ethylene oxide)-block-poly(3-hexylthiophene) with controlled molecular weight and low dispersity. Further, the combination of the conventional rod-first and newly developed coil-first approaches facilitated the straightforward synthesis of a unique ABC-type rod–coil–rod triblock copolymer that was limitedly accessible by other methods. We believe that this efficient and readily accessible synthetic platform would be highly useful for the preparation of novel conjugated rod–coil block copolymers that can be applied in optoelectronics, battery engineering, and chemical sensing.

Synthetic Concept of Intrinsically Elastic Luminescent Polyfluorene-Based Copolymers via RAFT Polymerization

An easy and novel synthetic concept for building intrinsically stretchable and elastic semiconducting polymers is designed in this study, in which a conjugated rod–coil block copolymer with a rigid...

Novel stretchable light‐emitting diodes based on conjugated‐rod block elastic‐coil copolymers

In this study, we successfully fabricated an intrinsically stretchable light‐emitting diode (LED) by using a new conjugated rod–coil block copolymer, poly[2,7‐(9,9‐dioctylfluorene)]‐block‐poly(isoprene) (PF‐b‐PI). ( PF conjugated rods and PI coils exhibited fluorescent and intrinsically stretchable properties, respectively. Copolymers with three different rod/coil ratios, namely PF18K‐b‐PI5K, PF12K‐b‐PI5K and PF12K‐b‐PI10K, were utilized for elastic LED demonstration. Notably, PF18K‐b‐PI5K and PF12K‐b‐PI5K LEDs can work under a strain of 140% because of suitable ratios of rod/coil lengths. Finally, a stretchable PF12K‐b‐PI5K LED was measured with a low voltage of 2 V and with a brightness of 70 cd m−2 at 10 V. This LED was subjected to 100 cycles of luminance–strain testing under 50% strain and it maintained a stable level of brightness. These results demonstrated that the luminescent PF12K‐b‐PI5K rod–coil block copolymers exhibit exceptional stretchability and high stability; these copolymers can be used in stretchable LEDs for a wide range of applications. © 2020 Society of Chemical Industry

Organocatalyzed Living Radical Polymerization of Itaconates and Self-Assemblies of Rod-Coil Block Copolymers.

Organocatalyzed living radical polymerizations of itaconates are studied, yielding low-dispersity linear and star polymers (Đ = Mw /Mn = 1.28-1.46) up to Mn = 20 000 and monomer conversion = 62%, where Mn and Mw are the number- and weight-average molar masses, respectively. The block polymerization with functional methacrylates, an acrylate, and styrene yields various rod-coil block copolymers. Linear A-B diblock, linear B-A-B triblock, and 3-arm star A-B diblock copolymers generate spherical micelles (nanoparticles) and vesicles (nanocapsules), depending on the polymer structures. Itaconates can be derived from bioresources, and thus the obtained polymers may serve as green polymers. Because of the biocompatibility of polyitaconates, the assemblies may serve as biocompatible nanocarriers.

Vertical Lamellae Formed by Two-Step Annealing of a Rod-Coil Liquid Crystalline Block Copolymer Thin Film.

Silicon-containing block copolymer thin films with high interaction parameter and etch contrast are ideal candidates to generate robust nanotemplates for advanced nanofabrication, but they typically form in-plane oriented microdomains as a result of the dissimilar surface energies of the blocks. Here, we describe a two-step annealing method to produce vertically aligned lamellar structures in thin film of a silicon-containing rod–coil thermotropic liquid crystalline block copolymer. The rod–coil block copolymer with the volume fraction of the Si-containing block of 0.22 presents an asymmetrical lamellar structure in which the rod block forms a hexatic columnar nematic liquid crystalline phase. A solvent vapor annealing step first produces well-ordered in-plane cylinders of the Si-containing block, then a subsequent thermal annealing promotes the phase transition from in-plane cylinders to vertical lamellae. The pathways of the order–order transition were examined by microscopy and in situ using grazing incidence small-angle X-ray scattering and wide-angle X-ray scattering.

Adsorption and ordering of amphiphilic rod-coil block copolymers on a substrate: conditions for well-aligned stripe nanopatterns.

Controlling the ordering of self-assembled nanostructures is vital in block copolymer nanotechnology but still presents a challenge. Here we demonstrated that the adsorption and ordering of amphiphilic rod-coil block copolymers on a substrate can generate well-aligned stripe nanopatterns by dissipative particle dynamics simulations. The effects of the copolymer concentration and the surface affinity on the formation of stripe nanopatterns were examined. The simulation results revealed that the well-aligned stripe nanopatterns with controllable thickness and stripe width can be obtained in the systems with higher copolymer concentration and surface affinity. An immersion coating experiment was designed to verify the simulation results, and an agreement is shown. The present work provides a strategy for constructing well-aligned stripe nanopatterns in a controllable way.

Target-Directed Design of Phase Transition Path for Complex Structures of Rod-Coil Block Copolymers.

We apply the string method to the self-consistent mean-field theory framework of the rod–coil block copolymer system to calculate the minimum energy pathways in the rearrangement transitions of lamellae and cylinders with different orientations under certain epitaxial growth relationship. Metastable phases appearing in the reordering transition pathway tend to form the structure at low χN side of the order–order transition boundary compared with the initial phase. In particular, for complex network, metastable phases, such as single gyroid and perforated lamellae, need to select a rearrangement transition between lamellae or cylinders near the order–disorder transition boundary with the same epitaxial growth relationship but different orientations. It is confirmed that this strategy for obtaining complex metastable phases by rational design of rearrangement transition between specific phases in the phase diagram can be applied to a wide range of χN as well as the coil–coil block copolymer system. We further investigate the rearrangement transition behavior combining with the analysis of contribution from the free energy, entropy, degree of mixing between different blocks, and the average orientation degree of rods during the phase transitions. Based on this mechanism, we have developed a target-directed design strategy for constructing self-assembled metastable structures of rod–coil block copolymers.

Ordered Surface Nanostructures Self-Assembled from Rod-Coil Block Copolymers on Microspheres.

An ordered surface nanostructure endows materials advanced functions. However, fabricating ordered surface-patterned particles via the polymer self-assembly approach is a challenge. Here we report that poly(γ-benzyl-l-glutamate)-block-poly(ethylene glycol) rod-coil block copolymers are able to form uniform-surface micelles on polystyrene microspheres through a solution self-assembly approach. The size of the surface micelles can be varied by the molecular weight of the block copolymers. These surface micelles are arranged in a manner consistent with the Euler theorem. Most of the micelles are six-fold coordinated, and the number difference between the five-fold and the seven-fold coordination is 12. Simulations on model systems qualitatively reproduced the experimental findings and provided direct observations for the surface-patterned particles, including the polymer chain packing manner in surface micelles at the molecular level and the array feature of the surface micelles through 2D projections of the surface patterns.

Enhancement of orientation of rigid polymer blocks by incorporating rod–coil block copolymer chains into metal–organic frameworks

AbstractIncorporation of polymer chains into metal–organic frameworks (MOFs) is a simple yet efficient method for improving the orientation of the polymer chains. However, due to their rigidity and high molecular weight, many rigid polymer chains are either not easily loaded into MOFs, or not easily aligned within the MOF channels. In this paper, we propose a strategy for enhancing the orientation of rigid blocks by incorporating rod–coil block copolymer chains into MOFs. In this strategy, on the one hand, the rigid blocks have a low molecular weight, so that the steric hindrance effect from the MOF channels could align the rigid blocks more efficiently. On the other hand, because the covalent bonds between the repeat units of the flexible blocks can rotate relatively easily, the steric hindrance effect from the flexible blocks can further help the rigid blocks to be oriented within the MOF channels. In confirmatory simulations, two all‐atom MOF models, [Zn2(BDC)2(TED)]n and [Zn2(BPDC)2(TED)]n (TED = triethylenediamine, BDC = 1,4‐benzenedicarboxylate, BPDC = 4,4′‐biphenyldicarboxylate), are established. With these MOF models, molecular dynamics simulations are performed for the rigid poly(phenylene vinylene) (PPV) chain and the rod–coil block copolymer PPV‐block‐polystyrene (PSt). Further, their respective degrees of orientation (DoOs) are calculated. Within [Zn2(BDC)2(TED)]n and [Zn2(BPDC)2(TED)]n, the DoOs of the rigid PPV blocks of PPV‐block‐PSt are 0.968 and 0.902, respectively, while the DoOs of the rigid PPV chains are 0.865 and 0.711, respectively. These calculation results prove the feasibility of our proposed strategy. © 2019 Society of Chemical Industry