Interplay of liquid crystalline ordering in double side-chain liquid crystalline diblock copolymer

Rational design and successful synthesis of a novel double side-chain liquid crystalline (SCLC) diblock copolymer bearing a common flexible polyether backbone were achieved via sequential anionic polymerization. The distinct differences in transition temperatures as well as phase ranges of the constituting blocks counterparts merited the full exploration of complex phase structures of the diblock copolymer in a potential non-segregation state. It was clearly demonstrated that the presence of a comparably strong LC phase domain of one block could prohibit the formation of an LC phase of the adjacent block, despite that the size incommensurateness of phase structures across the interface is only ∼0.3 nm. Moreover, it was observed that the existing LC phase could be disrupted with the evolution of the dominating LC phase domain of the neighboring block. Release of constraint from the dominating LC phase domain allowed the development of the originally suppressed LC phase.     

Manipulating ordered structure of ionic liquid crystalline polymers through tuning the alkyl spacer length

The fabrication of ordered structure is very important for the applications of ionic liquid crystalline polymers (ILCPs) or polymerized (ionic liquid crystal) (PILC). In this paper, we reported a facile approach to manipulate the ordered structure of ILCPs through adjusting the length of alkyl spacer. We designed and synthesized a series of ILCPs contained imidazolium, poly(2,5-bis{[m-(4-butoxy-4′-imidazolium phenyl) m-alkyl] oxy carbonyl} styrene bis (fluoroborate) salts) (denoted as P_4-m−BF₄, m represents the number of carbon in the alkyl spacers and m = 2, 4, 6, 10) via radical polymerization. Combined differential scanning calorimetry (DSC), polarized light microscopy (PLM), X-ray scattering, and two-dimensional wide-angle X-ray diffraction (2D WAXD), we found that the ordered structure of this ILCPs can transfer from smectic A phase (SmA) to hexagonal columnar (Φ_H) phase with the increase of spacer. Furthermore, these results were confirmed by reconstructed relative electron density map using fast fourier transform algorithm (FFT). The result revealed that the increase of alkyl spacer would affect the interaction between ions and side chain, and induce the packing of the side chains. It was evident that the alkyl spacer played an important role in the constructing of ordered structure and offered a new method to fabricate different ordered structure of ILCPs.     

Micellar morphologies of self-associated diblock copolymers in acetone solution

We describe the synthesis and solution morphologies of poly(vinyl phenol-b-styrene) (PVPh-b-PS) micelles and the effects that changing the copolymer composition and concentration have on self-assembly structures of PVPh-b-PS in acetone (a good solvent for PVPh). These PVPh-b-PS copolymers aggregated into spherical, rod-like, and vesicular morphologies. The transformations of the PVPh-b-PS block copolymer micelles in acetone depended on a number of parameters, including the relative block lengths, their concentrations, and the degree of self-association through hydrogen bonding of the coronal PVPh chains. We also investigated the morphologies of the micelles formed from acetone solutions of poly(4-tert-butoxystyrene-b-styrene) (PtBOS-b-PS) copolymers having the same degree of polymerization as the precursor of PVPh-b-PS copolymer before hydrolysis reaction. Our results indicate that the micelles formed from PVPh-b-PS copolymers in acetone were more complicated than those prepared from PtBOS-b-PS copolymers in acetone because hydrogen bonding occurs in the micelle corona of the PVPh block. Finally, we also discussed the morphology transition when the self-association hydrogen bonding of PVPh block was destroyed by adding proton acceptor poly(4-vinylpyridine) (P4VP).     

Phase behavior in liquid crystallization for diblock copolymers consisting of rubbery amorphous and side-chain liquid crystalline components

Phase behavior in liquid crystallization was studied for a series of liquid crystalline (LC) diblock copolymers consisting of rubbery amorphous and side-chain liquid crystalline components, poly(n-butyl acrylate) (PBA) and poly[11-(4′-cyanophenyl-4″-phenoxy)undecyl acrylate] (PLC), respectively, using a time-resolved small-angle X-ray scattering (SAXS) techniques, DSC and polarized optical microscopy (POM). The block copolymers used had three kinds of copolymer compositions, 44, 20 and 15 wt% of PLC compositions (BLC44, BLC20 and BLC15, respectively). BLC44 showed a smectic liquid crystalline structure. In the process of liquid crystallization for BLC44, the SAXS peak due to the microphase separation structure existing before liquid crystallization was changed continuously to be at a smaller angular side, and at almost the same time, a new peak appeared at a further smaller angular side and developed. The former peak disappeared with the development of liquid crystallization. The behavior of these SAXS peaks suggests that the microphase separation structure was changed discretely at the transition from isotropic to smectic and that two phases coexist in the early stage of the liquid crystallization. The coexistence of two peaks in the early stage of the liquid crystallization corresponded to the POM observation. In the isotropization process, coexistence of two phases was not observed. For BLC20 exhibiting a cylindrical structure in both isotropic and liquid crystalline states, the liquid crystalline structure was not smectic but probably nematic, and the spacing was changed continuously in liquid crystallization. No liquid crystallization was observed in SAXS, POM and DSC for BLC15. The orientation of smectic layers within lamellar domains was investigated using 2D-SAXS images. The smectic layer was aligned perpendicularly to the lamellar interface.     

Crystallization behavior of oxyethylene/oxybutylene diblock and triblock copolymers

The crystallization behavior of poly(oxyethylene)-b-poly(oxybutylene) block copolymers with different compositions, morphologies and architectures (E_mB_n diblock copolymers and E_mB_nE_m, B_nE_mB_n triblock copolymers) were investigated and the effect of volume fraction and architecture on the crystallization temperature (T_c) in non-isothermal crystallization was determined. It is found that the E_mB_n diblock copolymers having long E blocks exhibit similar crystallization temperatures, irrespective of volume fraction and morphology, but for the block copolymers with shorter E blocks the crystallization temperature increases with both the volume fraction, φ_E, and the length, m, of the E block. Some block copolymers with extremely low T_c, which fall into the temperature range normally associated with homogenous nucleation, were chosen for time-resolved small-angle X-ray scattering (SAXS) and isothermal crystallization kinetics experiments. The results show that breakout crystallization occurs in all these block copolymers. Therefore, unlike E_mB_n/B_h blends, there is no obvious relationship between T_c and crystallization behavior in neat block copolymers and homogeneous nucleation does not definitely lead to confined crystallization. The values of χ_c/χ_ODT for all the block copolymers with hex and bcc morphology were also calculated. It is found that all the block copolymers have χ_c/χ_ODT<3, in agreement with the previously reported critical value and consistent with their breakout crystallization behavior.     

Proton conducting membrane containing room temperature ionic liquid

A new proton conducting membrane containing room temperature ionic liquid: 2,3-dimethyl-1-octylimidazolium trifluoromethanesulfonylimide (DMOImTFSI) and polyvinylidenefluoride-co-hexafluoropropylene (PVdF-HFP) has been developed in the present work. The addition of bis(trifluoromethanesulphonyl)imide (HN(CF₃SO₂)₂) to this membrane results in an increase in conductivity by one order of magnitude at 25 °C. The membrane shows a conductivity of 2.74 × 10⁻³ S/cm at 130 °C along with good mechanical stability. The membrane was tested in a commercial fuel cell test station at 100 °C with dry hydrogen and oxygen gas reactants using Pt/C electrodes. The membrane containing the ionic liquid has been found to be electroactive for hydrogen oxidation and oxygen reduction at the platinum electrode and can be developed for use in proton exchange membrane fuel cell (PEMFC) under non-humid conditions at elevated temperatures.     

Block copolymer/ionic liquid films: The effect of ionic liquid composition on morphology and ion conduction

The effect of morphology on ion transport in ionic liquid-based solid-state films was investigated. In this study, mixtures of a block copolymer, poly(styrene-b-methyl methacrylate) (SbMMA), and an ionic liquid (IL), 1-ethyl-3-methylimidazolium bis (trifluoromethylsulfonyl)imide (EMIm-TFSI), were prepared as clear solid-state films at various IL compositions (0-50 wt%) by solution casting from a volatile co-solvent. The IL was preferentially miscible with the MMA block as evidenced by visual inspection and differential scanning calorimetry. Both equilibrium and non-equilibrium morphologies were identified with X-ray scattering and transmission electron microscopy and the morphology varied with MMA/IL volume fraction. The morphology and microdomain orientation had a significant impact on ionic conductivity. Higher through-plane conductivities were observed in morphologies with a three-dimensionally continuous conducting path (e.g., non-conducting S cylinders) compared to morphologies with a non-continuous conducting path (e.g., lamellae). When the lamellae were oriented in the plane, the through-plane conductivity was significantly lower than the in-plane conductivity, while the conductivity was direction-independent when the morphologies have a continuous conductive path. Also, a significant increase in conductivity was observed with increasing IL content at the glass transition of the conductive (MMA/IL) microdomain. Finally, significantly higher ionic conductivities can be achieved in a block copolymer/IL solid-state film compared to a homopolymer/IL film at the same IL content (wt%), because the non-conductive microdomain excludes IL, which produces a higher local IL concentration in the conductive phase.     

Phase behavior and structure formation for diblock copolymers composed of side-chain liquid crystalline and glassy amorphous components

Phase behavior and structure formation in liquid crystallization of a side-chain liquid crystalline (LC) block copolymers composed of poly[11-(4′-cyanophenyl-4″-phenoxy)undecyl acrylate] (PA₁₁OCB) and polystyrene (PSt) were investigated by using a time-resolved small-angle X-ray scattering technique (SAXS), differential scanning calorimetry and polarizing optical microscopy. PA₁₁OCB homopolymer formed smectic (Sm) liquid crystal. Liquid crystallization behavior of the block copolymers depended on the molecular weight and the block composition. When molecular weight was relatively low, order-disorder transition (ODT) was observed. In cooling of such block copolymers, liquid crystallization seemed to wait for the formation of LC-rich microphase by ODT. For the block copolymers with relatively high molecular weight, liquid crystallization slightly enlarged the domain spacing without changing the microphase separation structure in the melt. The order of the LC phase was lowered with decreasing dimensionality of the LC microdomains, that is, the LC blocks formed smectic liquid crystal in the matrix or lamellar microphase while liquid crystallization in the cylindrical microdomains did not show smectic but maybe nematic liquid crystal. Moreover, the LC blocks within the spherical microdomains did not liquid crystallize. From the 2-D SAXS with applying shear flow, the Sm layers were orientated perpendicularly to the interface of the microphase separation. The relation between the layer thickness of the LC phase and the molecular weight suggested that the main chain was extended normally to the interface of the microphase separation.     

Improved ionic conductivity of nitrile rubber/ionic liquid composites

Polymer electrolytes with high ionic conductivity and good elasticity were prepared by mixing nitrile rubber (poly(acrylonitrile-co-butadiene) rubber; NBR) with ionic liquid, N-ethylimidazolium bis(trifluoromethanesulfonyl)imide (EImTFSI). The NBR/EImTFSI composites were obtained as homogeneous and transparent films when the ionic liquid content was less than 60 wt%. Raman spectroscopy suggested the interaction between nitrile group of NBR and TFSI anion. Sample with ionic liquid content of 50 wt% showed the ionic conductivity of 1.2×10⁻⁵ S cm⁻¹ at 30 °C. Addition of lithium salt to this NBR/EImTFSI composite further enhanced the ionic conductivity to about 10⁻⁴ S cm⁻¹ without spoiling mechanical properties. DSC studies showed two glass transition temperatures for composites indicating microphase separation.     

Synthesis and characterization of side-chain liquid crystalline homopolymers and block copolymers containing biphenyl-4-ylthiophene and biphenyl-4-ylfluorene pendants

A series of new liquid crystalline homopolymers (P1 and P2) and block copolymers (P3 and P4) composed of methacrylates containing pendant biphenyl-4-ylthiophene (M1) and biphenyl-4-ylfluorene (M2) units were synthesized by atom transfer radical polymerization (ATRP). The number-average molecular weights (M_n) of the homopolymer (P2) and diblock copolymers (P3 and P4) were in the range of 5153-8713 g mol⁻¹ with polydispersity indices (PDIs) between 1.17 and 1.25. The thermal, mesogenic, and photoluminescence (PL) properties of all polymers were investigated. Except for the absence of mesogenic properties in block copolymer P4, polymers P1 and P3 possessed the smectic A phase and polymer P2 exhibited the nematic phase. Moreover, the mesomorphism and the layer d-spacing values of the smectic A phase in polymers P1 and P3 were confirmed and characterized by X-ray diffraction (XRD) patterns.     

Anion exchanged polymerized ionic liquids: High free volume single ion conductors

In this study, we investigate the isolated effect of anion type on the chemical, thermal, and conductive properties of imidazolium-based polymerized ionic liquids (PILs). PILs with various anions at constant average chain length were prepared by ion exchange with a water-soluble PIL precursor, (poly(1-[(2-methacryloyloxy)ethyl]-3-butylimidazolium bromide) (poly(MEBIm-Br)). NMR, IR, and elemental analysis confirm that anion exchange of ploy(MEBIm-Br) with bis(trifluoromethanesulfonyl) imide (TFSI), tetrafluoroborate (BF₄), trifluoromethanesulfonate (Tf), and hexafluorophosphate (PF₆) in water resulted in nearly fully exchanged PILs. As a function of anion type, the glass transition temperature plays a dominant role, but not the sole role in determining ion conductivity. Other factors affecting ionic conductivity include the size and symmetry of the anion and dissociation energy of the ion pair. Both the Vogel-Fulcher-Tammann (VFT) and Williams-Landel-Ferry (WLF) equations were employed to investigate the temperature dependent ionic conductivities. The (9.03) and (168 K) values obtained from the WLF regression of these PILs greatly deviate from the classical WLF values originally obtained from the mechanical relaxation of uncharged polymers ( = 17.44,  = 51.6 K) and the WLF values obtained from the conductive properties of other polymer electrolytes. This suggests that the fractional free volume (f (T_g) = B/(2.303)) and Vogel temperature (T₀ = T_g − ) are strong functions of ion concentration, where high free volume allows for ion mobility at temperatures farther below the glass transition temperature of the polymer.     

Ordered,microphase-separated,noncharged-charged diblock copolymers via the sequential ATRP of styrene and styrenic imidazolium monomers

A series of imidazolium-based noncharged-charged diblock copolymers (1) was synthesized by the direct, sequential ATRP of styrene and styrenic imidazolium bis(trifluoromethyl)sulfonamide monomers with methyl, n-butyl, and n-decyl side-chains. Small-angle X-ray scattering studies on initial examples of 1 with a total of 50 repeat units and styrene:imidazolium-styrene repeat unit ratios of 25:25, 20:30, and 15:35 showed that their ability to form ordered nanostructures (i.e., sphere and cylinder phases) in their neat states depends on both the block ratio and the length of the alkyl side-chain on the imidazolium monomer. To our knowledge, the synthesis of imidazolium-based BCPs that form ordered, phase-separated nanostructures via direct ATRP of immiscible co-monomers is unprecedented.     

Syntheses and characterizations of the multiple morphologies formed by the self-assembly of the semicrystalline P4VP-b-PCL diblock copolymers

A series of semicrystalline diblock copolymers of poly(4-vinylpyridine-b-?-caprolactone) (P4VP-b-PCL) have been synthesized by the living ROP of CL followed by the TEMPO polymerization of 4-VP. Depending on the relative block length and different solvent compositions, these copolymers self-assemble into different supramolecular structures in toluene/dichloromethane (DCM) solution, including spherical micelles, bowl-shaped vesicles, multilayer vesicles, porous spheres, and large compound micelles. In methanol/DCM solution system, the crystalline PCL core disturbs the balance of free energy, thus results in a series of morphological changes including spherical micelles, worm-like rods, vesicles, coexisted vesicles and lamella, and finally platelet lamella.     

Ionic conductivity, infrared and Raman spectroscopic studies of 1-methyl-3-propylimidazolium iodide ionic liquid with added iodine

Polyiodides (I_x⁻, x = 3 and 5) and 2I⁻…I₂ adducts were established from the Raman spectra study of 1-methyl-3-propylimidazolium iodide (MPIm⁺I_x⁻; 1 ≤ x ≤ 5) ionic liquids containing various amounts of iodine (0 mol ≤ I₂ ≤ 2 mol). The existence of I₃⁻ and 2I⁻…I₂ was established for 1 ≤ x ≤ 2.5, symmetric I₃⁻ ions for x = 3, while linear and discrete I₅⁻ was substantiated for 3 ≤ x ≤ 5. The presence of polyiodide species in MPIm⁺I_x⁻ (1 ≤ x ≤ 5) was correlated with an enhanced ionic conductivity, attributed to the established relay-type Grotthus mechanism. Two-step conductivity increase was also reflected in decrease of the hydrogen bond interactions between the CH ring groups and polyiodides. While in the concentration range 1 ≤ x ≤ 3 (triiodides and tetraiodides) IR bands changed only slightly in intensity, in the concentration range x > 3 the CH stretching bands (3040-3170 cm⁻¹) split and the new band at 1585 cm⁻¹ appeared in the IR spectra beside the already existing Im⁺ ring stretching mode at 1566 cm⁻¹.     

Self-assembly of an A-B diblock copolymer blended with a C homopolymer and a C-D diblock copolymer through hydrogen bonding interaction

In this study, we investigated the miscibility, phase behavior, and self-assembled nanostructures formed from the immiscible crystalline-amorphous diblock copolymer poly(?-caprolactone-b-4-vinyl pyridine) (PCL-b-P4VP, A-B) when blended with the homopolymer poly(vinyl phenol) (PVPh, C) and the diblock copolymer poly(vinyl phenol-b-styrene) (PVPh-b-PS, C-D). Long-range-ordered microphase separation was difficult to achieve in the PCL-b-P4VP/PVPh (A-B/C) blend system because PVPh interacted with both the P4VP and PCL blocks simultaneously through hydrogen bonding interactions. In contrast, we observed sharp, multiple orders of diffraction in the SAXS profiles of the PCL-b-P4VP/PVPh-b-PS (A-B/C-D) blend system, indicating that perfect microphase separation occurred because the incorporation of the PS block induced the PVPh block to hydrogen bond preferentially with the P4VP block. This simple A-B/C-D (PCL-b-P4VP/PVPh-b-PS) diblock copolymer mixture exhibited self-assembly behavior (a three-lamella phase) similar to that of a corresponding ABC triblock copolymer.     

A novel polymeric gel electrolyte systems containing magnesium salt with ionic liquid

A new polymeric gel electrolyte system consisting of poly(ethylene oxide)-modified polymethacrylate (PEO-PMA) with organic ionic liquid dissolving magnesium salt, Mg[(CF₃SO₂)₂N]₂, has been developed. The ionic conductance and electrochemical properties of the gel films were investigated. The obtained gel film was self-standing, transparent and flexible with sufficient mechanical strength. Thermal analysis of the gel film showed that it is homogeneous and amorphous over a wide temperature range. The highest conductivity, ca. 3.5 mS cm⁻¹ at 60 °C, was obtained for the polymeric gel containing 80 wt.% of the liquid component that consists of 80 mol% of EMITFSI (1-ethyl-3-methylimidazolium bis(trofluoromethylsulfonyl)imide) and 20 mol% of Mg[(CF₃SO₂)₂N]₂. The sort of the ionic liquid affected much on the ionic conductivity of the gel. The dc polarization of a Pt/polymeric gel electrolyte/Mg cell proved that the magnesium ion (Mg²⁺) can mobile in the present polymeric gel system.     

Syntheses and specific interactions of poly(hydroxyethyl methacrylate-b-vinyl pyrrolidone) diblock copolymers and comparisons with their corresponding miscible blend systems

Combination of atom transfer radical and conventional free radical polymerizations has been successfully used to prepare poly(hydroxyethyl methacrylate-b-vinyl pyrrolidone) (PHEMA-b-PVP) copolymers with controlled molecular weight and low polydispersity (<1.4). The thermal behavior and specific interaction of PHEMA-b-PVP diblock copolymers and their corresponding PHEMA/PVP blends were characterized. The result shows that glass transition temperatures of diblock copolymers analysed by differential scanning calorimetry (DSC) are higher than those of the blends. Infrared and solid-state NMR spectroscopic analyses show that hydrogen-bonding interaction of hydroxyl-carbonyl groups of diblock copolymers was also greater than that of the blends. Measurement of the proton spin-lattice relaxation time in the rotating frame, , reveals that all diblock copolymers and blends possess one composition-dependent , indicating that both diblock copolymers and blends are homogeneous, which is consistent with the DSC analysis.     

Synthesis and characterization of all-conjugated diblock copolymers consisting of thiophenes with a hydrophobic alkyl and a hydrophilic alkoxy side chain

Novel thiophene-based all-conjugated block copolymers consisting of 3-hexylthiophene and 3-{2-[2-(2-methoxyethoxy)ethoxy]ethoxy}thiophene were synthesized using the Grignard metathesis (GRIM) polymerization method in the presence of Ni(dppp)Cl₂. Favorable transfer of the catalytic site from an electron-poor precursor to an electron-rich monomer was found to produce the block copolymer. The molecular weights of the copolymers increased slightly with increasing polymerization temperature (10.1 × 10³M_n (35 °C) → 11.1 × 10³M_n (55 °C)), suggesting that transit of the catalytic site was accelerated at high temperatures. Size exclusion chromatography, UV-vis and photoluminescence spectroscopies, and cyclic voltammetry measurements confirmed that the polymers were block copolymers. The blocks were associated and organized relative to one another in adjacent chains.     

Phase behavior and microstructural length scales of a diblock copolymer in the presence of a selective solvent

We employ self-consistent mean-field (SCMF) theory in studying the phase behavior as well as the microstructural domain sizes for a diblock copolymer in the presence of a selective solvent. First we examine the effects of solvent addition on the formation of fcc and bcc packed spheres. As has been found in experiments, the so-called “normal” spheres, i.e., formed by the minority blocks, tend to pack into the bcc array, while the “inverted” spheres formed by the majority blocks favor the fcc packing. Upon increasing the solvent selectivity and/or solvent amount, the formed inverted spheres tend to pack from bcc to fcc. This thermotropic transition of bcc → fcc upon increasing the solvent selectivity is induced by the fact that the intermicellar interactions vary from long-range to short-range via a combination of the solvent exclusion from the cores and an increase in the aggregation number. In analyzing the effects of solvent addition on the microstructural sizes, the SCMF results have successfully captured the crossover behavior of characteristic domain spacing from decreasing with added solvent to increasing by increasing the solvent selectivity. Further, the variation of the characteristic domain spacing when the systems transform to a more curved structure changes from a discontinuous decreasing behavior to even a discontinuous increasing behavior upon increasing the solvent selectivity and/or the formation of inverted structures.     

Preparation and characterization of novel ionic liquid based on benzotriazolium cation

Six novel ionic liquids based on benzotriazolium ion were synthesized by an improved method. These ionic liquids were characterized by IR, ¹H NMR, and elemental analysis. Their melting point, thermal stability, conductivity, electrochemical window and solubility properties in common solvents were investigated. The results indicate that these ionic liquids show the higher thermal stability (up to 345 °C), the larger electrochemical window of 3 V, the peculiar solubility in traditional solvents and the excellent electrochemical medium in the electrochemical oxidation of naphthalene and ferrocene.