Mesogen-jacketed Liquid Crystalline Polymers Research Articles

Design, synthesis and properties of mesogen jacketed liquid crystalline polymers with fluorinated triphenylene pendants

Discotic liquid crystalline polymers (DLCPs) combining the advantages of discotic liquid crystals and polymers yet have been less developed compared to the calamitic counterparts mainly due to lack of DLCP materials. Here, mesogen-jacketed liquid crystalline polymers with pendant fluorinated triphenylene were successfully synthesized via proper polymerizations of the corresponding monomers respectively. Nuclear magnetic resonance spectroscopy (both 1H NMR and 13C NMR), time-of-flight mass spectrometry (MALDI-TOF MS), Fourier transform Infrared (FT-IR) spectroscopy and other characterization methods were used to confirm the structure of the products. The mesomorphic properties of the obtained triphenylene monomers with unsaturated flexible tails and resulting polymers were investigated by polarizing optical microscopy (POM), differential scanning calorimetry (DSC), and X-ray diffractometer (XRD). The propargylene-containing monomer shows a smectic liquid crystals phase and the pentynylene monomer exhibit a highly ordered columnar helical liquid crystal phase. The three side chain polymers containing fluorinated triphenylene have good thermal stability (decomposition temperature of 350 °C or above). At the same time, the polymers prepared by the polymerization of propargylene-containing monomers have both hexagonal columnar phase (Colh) and rectangular columnar phases (Colr). The polymers with long spacer chains derived from Methyl acrylate have a hexagonal columnar structure (Colh). The fluorinated triphenylene monomers and polymers with ordered liquid crystal phases synthesized in this work provide useful inspiring for structural modifications of DLCPs and are promising for applications in organic optoelectronics.

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.

Hierarchically Ordered Structures of Rod–Rod Block Copolymers Containing Two Mesogen-Jacketed Liquid Crystalline Polymers

In order to investigate the factors affecting the hierarchically ordered structures of the rod–rod block copolymers, SmPn based on two polynorbornene-based mesogen-jacketed liquid crystalline (LC) polymers PNb12POSS [having side-chain polyhedral oligomeric silsesquioxane (POSS) units] and PNb10PP (with a side-chain calamitic mesogen) was designed and synthesized by ring-opening metathesis polymerization, in which S and P refer to the two segments PNb12POSS and PNb10PP, respectively, whereas m and n refer to the ratios of monomer to catalyst during polymerization of PNb12POSS and PNb10PP, respectively. Investigation on the phase structures and behaviors of SmPn samples indicates that the LC and crystalline structures of the two segments are similar to their homopolymers. The PNb10PP segment forms a smectic A (SmA) phase with the ordered packing of the rod-like mesogens, and the PNb12POSS segment forms a hexagonal columnar (Colh) phase with the crystal of POSS units. The volume fraction of PNb12POSS (fPNb12POSS) plays an important role on the microphase separation of SmPn. The asymmetry between the two blocks becomes more pronounced with increasing fPNb12POSS, resulting in a larger bending curvature, and the microphase-separated structure changes from lamellar (LAM) to hexagonally packed cylinders (HEX) for S10P30, S20P30, and S30P30. Moreover, the PNb12POSS segments in S20P30 and S30P30 form Colh phases that can be clearly observed by transmission electron microscopy. However, because of the slow kinetics of the polymer chains owing to the high molecular weight and rigidity, sample S30P120 having the lowest fPNb12POSS value cannot form ordered structures, while S80P120 only forms a HEX structure lacking regularity with a size of ∼40 nm.

Phase Behavior of Phasmidic Mesogen-Jacketed Liquid Crystalline Polymers Displaying Chain Bundling

Phasmidic mesogens generally consist of a long rod core and two dendronized end-groups possessing three alkyl tails. Mesogen-jacketed liquid crystalline polymers (MJLCPs) represent an important cla...

Core–Shell and Zigzag Nanostructures from a Thin Film Silicon-Containing Conformationally Asymmetric Triblock Terpolymer

The self-assembly of multiblock copolymers generates diverse hierarchical nanostructures and greatly extends the range of microdomain geometries beyond those produced by diblock copolymers. We report the synthesis of a conformationally asymmetric ABC triblock terpolymer in which the end blocks are a mesogen-jacketed liquid crystalline polymer and poly(dimethylsiloxane), respectively, and its self-assembly under mixed solvent vapor annealing forms a range of sphere, cylinder, and perforated lamellar core-shell morphologies, as well as stacked multilevel structures. Sub-7 nm diameter SiOx nanopatterns were generated by selective plasma etching of the small volume fraction Si-containing core block giving a line/space ratio of ∼1:4. Moreover, the conformational asymmetry of this terpolymer leads to zigzag cylinders on a flat substrate and stable cylinder alignment transverse to template sidewalls within lithographically patterned trenches.

Self-assembly and Properties of Block Copolymers Containing Mesogen-Jacketed Liquid Crystalline Polymers as Rod Blocks

Mesogen-jacketed liquid crystalline polymer (MJLCP) has attracted great attention because of its rigid conformation, facile synthesis, and structural controllability. In this feature article, the self-assembly of MJLCP-based block copolymers (BCPs) is briefly reviewed, especially the nanostructures of rod-coil diblock copolymers (diBCPs), rod-rod diBCPs, and triblock copolymers. In addition, the properties of the self-assembled BCPs are also summarized, including their applications as liquid crystalline thermoplastic elastomers and solid polymer electrolytes. The article also discusses the major challenges and future directions in the study of MJLCP-based BCPs.

Synthesis and properties of a new high-temperature liquid crystalline thermoplastic elastomer based on mesogen-jacketed liquid crystalline polymer

In order to obtain high-temperature resistant thermoplastic elastomers (TPEs), we designed and synthesized a new kind of ABA triblock copolymer containing a mesogen-jacketed liquid crystalline polymer, poly(4′-(methoxy)-2-vinylbiphenyl-4-methyl ether) (PMVBP), as the hard blocks and polybutadiene (PB) as the soft block. PB was synthesized by ring-opening metathesis polymerization in the presence of a chain transfer agent, and PMVBP was synthesized by nitroxide-mediated radical polymerization. The glass transition temperature of the PMVBP block is 186–211 °C, which is much higher than that of polystyrene. More importantly, PMVBP can maintain its liquid crystallinity even when the temperature is as high as 270 °C, which can enhance the mechanical properties of TPEs based on PMVBP, especially at high temperatures. All the resulting PMVBP-PB-PMVBP triblock copolymer samples form lamellar microphase-separated structures after combined treatment of solvent annealing and thermal annealing. They are good candidates for TPEs with a high operating temperature of more than 200 °C.

Precise size control of sub-10 nm structures of cholesteryl-containing mesogen-jacketed liquid crystalline polymers

A series of mesogen-jacketed liquid crystalline polymers (MJLCPs) with polynorbornene as the main chain and cholesteryl mesogenic units at the ends of the side chain, PNbnChol (n = 1, 3, 5, which is the number of benzene rings in the rigid side-chain core), were prepared by ring-opening metathesis polymerization. The phase behaviors of the polymers were investigated by differential scanning calorimetry, polarized light microscopy, and one-dimensional/two-dimensional X-ray scattering. The polymer with one benzene as the rigid core in the side chain shows only a smectic phase with interdigitated packing of cholesteryl units at low temperatures and is amorphous at high temperatures. While polymers containing three or five benzenes in the rigid side-chain core provide two different SmA phases at different temperatures, a smectic phase with double-layer-like packing of cholesteryl units at low temperatures and the smectic phase with interdigitated packing of cholesteryl units at high temperatures. The introduction of cholesteryl to MJLCPs can fabricate precisely controlled sub-10 nm scale ordered structures that can be maintained at high temperatures.

Synthesis and Characterization of New Liquid Crystalline Thermoplastic Elastomers Containing Mesogen-Jacketed Liquid Crystalline Polymers

In order to improve the high-temperature performance of thermoplastic elastomers (TPEs), we designed and synthesized a new kind of ABA triblock copolymer containing a mesogen-jacketed liquid crystalline polymer (MJLCP), poly{2,5-bis[(4-methoxyphenyl)oxycarbonyl]styrene} (PMPCS), as the hard blocks and polybutadiene (PB) as the soft block. The triblock copolymer, PMPCS-b-PB-b-PMPCS (M-B-M), was synthesized by ring-opening metathesis polymerization in the presence of a chain transfer agent and atom transfer radical polymerization. The glass transition temperature (Tg) of the PMPCS hard block is 110–118 °C in the triblock copolymers. In addition, the liquid crystalline (LC) phase of PMPCS is stable before thermal decomposition. All the triblock copolymers form lamellar microphase-separated structures, as demonstrated by small-angle X-ray scattering and transmission electron microscopy results. The triblock copolymer (M-B-M-55) with a mass fraction of 55% of PMPCS exhibits typical properties of an LC thermopl...

Effects of main chain and acceptor content on phase behaviors of hydrogen-bonded main-chain/side-chain combined liquid crystalline polymers

Main-chain/side-chain combined liquid crystalline polymers (MCSCLCPs) are usually difficult to synthesize and their degrees of polymerization are relatively low, which bring difficulties in studying their structure–property relationships. In order to solve this problem, we prepared a new series of MCSCLCPs containing mesogen-jacketed liquid crystalline polymer (MJLCP) main chains via hydrogen-bonding (H–B). A pyridine derivative with a triphenylene (Tp) unit is the H–B acceptor. In addition to the temperature dependence, the phase behavior of the resulting complex is strongly influenced by the content of the H–B acceptor and the rigidity of the side-chain core of the MJLCP. The resulting complexes exhibit different phase structures: (1) a columnar nematic phase or a smectic A (SmA) phase formed by the supramolecular MJLCP chain as a whole; (2) hierarchical nanostructures including a hexagonal columnar phase or a SmA phase of the whole polymer chain plus a discotic nematic phase associated with the Tp moieties.

Influence of the side-chain structure and molecular weight on the re-entrant behaviors of mesogen-jacketed liquid crystalline polymers

The influence of the alkyl spacer length and the terminal group volume influence on the phase behavior and structure of mesogen-jacketed liquid-crystalline polymers.

The molecular mechanism of the thermo-responsive shape memory effect of self-assembled poly-{2,5-bis[(4-butoxyphenyl)oxycarbonyl]styrene} fiber

A new molecular mechanism is proposed to explain the shape memory effect of mesogen-jacketed liquid crystalline polymer fiber—poly-{2,5-bis[(4-butoxyphenyl)oxycarbonyl]styrene} (PBPCS) fiber-designed in the molecular level. Due to the strong “coupling effect” between flexible backbone and rigid side mesogens, the molecular structure of PBPCS can be regarded as “dual chains” model that is constituted by a flexible backbone chain and a rigid side chain in parallel. The flexible backbone chains are reversible above the transition temperature and act as a switch structure, the physically cross-linked points caused by the π–π weak interactions between rigid side mesogens are responsible for memorizing a shape function and act as a fixing structure; therefore, the switch structure (flexible backbone) and the fixing structure (rigid mesogens) are found in each macromolecular chain. Furthermore, the shape memory behavior of PBPCS fibers is discussed by a viscoelastic molecular model consisting of two Maxwell models in parallel, the obtained theoretical values by “dual chains” model was in agreement with experimental results, very well. The viscoelastic molecular model described for shape memory process was correlated to the molecular mechanism explained for shape memory effect. This work provides a new idea and significant approach for design of new shape memory polymers.

The enhancing effect of mesogen-jacketed liquid crystalline polymer PBPCS on epoxy resin

The mixtures of mesogen-jacketed liquid crystalline polymers (MJLCP) and epoxy resin (E-51) have been prepared in a certain proportion. The category of the MJLCP is poly{2, 5-bis[(4-butoxyphenyl) oxycarbonyl] styrenes} (PBPCS). Methyl tetrahydro phthalic anhydride (MeTHPA) is served as a curing agent, and N, N-dimethylbenzylamine plays the role of catalyst. Then, based on the curing process, the modified materials have been acquired by casting molding. The effect of PBPCS's improvement has been researched through the mechanical properties test, dynamic thermal mechanical test and scanning electron microscope (SEM). The results indicated that PBPCS could apparently improve the mechanical properties of resin E-51. Compared with unmodified materials, the elongation at break and the tensile strength of PBPCS have been improved remarkably through modification. Both mechanical properties of the 4wt% PBPCS/E-51/MeTHPA were enhanced by 48% and 153% separately, and the characteristics of the 3wt% one were raised by 47% and 19% respectively. Also, the ductile fracture morphology of the resins was exhibited in SEM photograph clearly.

POSS-Containing Jacketed Polymer: Hybrid Inclusion Complex with Hierarchically Ordered Structures at Sub-10 nm and Angstrom Length Scales

A series of organic–inorganic hybrid polymers, PnPOSS (n = 6, 10, which is the number of carbon atoms in the flexible alkyl spacers), containing a mesogen-jacketed liquid crystalline polymer (MJLCP) as the main chain and a crystalline nanobuilding block, polyhedral oligomeric silsesquioxane (POSS), in the side chains were designed and synthesized for constructing a hybrid inclusion complex. The phase structures and phase transitions of PnPOSS were investigated by differential scanning calorimetry, polarized light microscopy, wide-angle X-ray diffraction, small-angle X-ray scattering, and high-resolution transmission electron microscopy. With the competitive self-assemblies of the two covalently connected building blocks, namely MJLCP and POSS moieties, PnPOSS shows various phase structures including a sub-10 nm hexagonal columnar (Colh) or columnar nematic liquid crystalline phase, an angstrom rhombohedral crystalline (KR) phase, and a hierarchically ordered phase with Colh and KR coexisting. This work provides a new approach for the design and synthesis of hybrid inclusion materials.

Mechanical and thermal properties of mesogen-jacketed liquid crystalline polymer/epoxy resin composites

The effects of mesogen-jacketed liquid crystalline polymer poly(dipropyl vinylterephthalate) (PDPVT) on the mechanical and thermal properties of diglycidyl ether of bisphenol-A (DGEBA) epoxy resin were investigated by impact test, tensile test and thermogravimetric analysis (TGA). The mechanism underlying the enhancement of mechanical properties of epoxy resin was studied using 1D wide-angle X-ray diffraction (WAXD) and scanning electron microscope (SEM). It was found that the mechanical properties of 1 wt%–5 wt% PDPVT/DGEBA composites were significantly improved compared to neat epoxy resin. Especially, the epoxy resin with 3 wt% PDPVT had the greatest increase in mechanical properties, with the impact strength, tensile strength and elongation while breaking increased by 87%, 59% and 174%, respectively. The increased mechanical strength was due to the fact that PDPVT maintained liquid crystalline phase in cured PDPVT/DGEBA composites, which would blunt the crack tip and prevent crack propagation. Moreover, PDPVT had slight effect on the thermal stability properties of epoxy resin.

Effects of rigid cores and flexible tails on the phase behaviors of polynorbornene-based mesogen-jacketed liquid crystalline polymers

MJLCPs with a polynorbornene main chain and different side groups have been precisely synthesized for investigating the effect of side-chain structures on the liquid crystalline phase behaviors.

Synthesis and sub-10 nm supramolecular self-assembly of a nanohybrid with a polynorbornene main chain and side-chain POSS moieties

A polynorbornene-based mesogen-jacketed liquid crystalline polymer containing side-chain crystalline POSS moieties was synthesized through ROMP. It self-assembles into an organic–inorganic hybrid inclusion complex on the sub-10 nm scale.

Influence of the spacer length on the phase behaviors of mesogen-jacketed liquid crystalline polymers with a bulk side-chain

The alkyl spacer length influences the phase behavior and structure of mesogen-jacketed liquid-crystalline polymers with bulk side-chains.

Mesogen-Jacketed Liquid Crystalline Polymers with a Polynorbornene Main Chain: Green Synthesis and Phase Behaviors

We synthesized a new series of MJLCPs with a polynorbornene main chain, PNbnPT (n = 8, 10, 12, 14, 16, 18, which is the number of carbons in the side-chain alkyl tails), through ring-opening metathesis polymerization and investigated their phase behaviors. The monomers were facilely synthesized in satisfactory yields through a key intermediate, N-(2,5-dicarboxylphenyl)-cis-5-norbornene-exo-2,3-dicarboximide. Differential scanning calorimetry, polarized light microscopy, and wide-angle X-ray diffraction results demonstrate that the phase behavior of PNbnPT is strongly dependent on the alkyl-tail length. Polymers with relatively short alkyl tails, PNb8PT and PNb10PT, are amorphous in the whole temperature range before degradation. When the alkyl-tail length increases, PNbnPTs (n = 12, 14, 16, 18) develop into the smectic A phase, and the degree of order increases with increasing alkyl-tail length. The synthetic pathway for MJLCPs with a polynorbornene main chain in this work is more robust and greener than those reported to the best of our knowledge. And MJLCPs with a polynorbornene main chain show quite different phase behaviors compared with those with a polyethylene backbone, and they may be used to create fascinating functional materials.

Synthesis and Phase Structures of Dendronized Polymers with Dendritic Azobenzene Side Groups Based on Mesogen-Jacketed Liquid Crystalline Polymers

The first- and second-generation dendronized polymers, poly (2, 5-bis {[3, 5-di (4′-methoxy-4-oxyhexyloxy azobenzene) benzyl] oxycarbonyl} styrene) (PG1) and poly (2, 5-bis {3, 5-di [3, 5-di (4′-methoxy-4-oxyhexyloxy azobenzene) benzyl] oxycarbonyl} styrene) (PG2), were successfully synthesized, and their phase structures were investigated by differential scanning calorimetry (DSC), polarized light microscopy (PLM), and one-dimensional wide-angle X-ray diffraction (1D WAXD). The results show that the liquid crystalline (LC) phase structures of the dendronized polymers containing dendritic azobenzene side groups depend strongly on the molecular weights (MWs) and the generation of dendritic azobenzene side groups. Compared the low MWs PG2 with the low MWs PG1, the degree of order in LC phase increased with increasing the generation of dendritic azobenzene side groups.