Search

A series of symmetrically tapered 1,4-bis[3,4,5-tris(alkan-1-yloxy)benzamido] benzene bisamides (CPhBA, where is the number of carbon atoms in the alkyl chains, = 10, 12 and 16), was synthesized in order to investigate the effect of alkyl chain length on supra-molecular ordered structures induced by hydrogen (H)-bonding and micro-phase separation. These bisamides consist of a rigid aromatic bisamide core with three flexible alkyl chains at each end of the core. Major phase transitions and their origins in CPhBA bisamides were studied with differential scanning calorimetry, one-dimensional (1D) wide angle X-ray diffraction (WAXD), infrared spectroscopy, and solid-state carbon-13 nuclear magnetic resonance experiments. The structures of these compounds in different phases were identified using 2D WAXD from oriented samples and were also confirmed by selected area electron diffractions in transmission electron microscopy from stacked single crystals and by computer simulations. All of the CPhBA bisamides in this series formed a highly ordered oblique columnar () phase and a low-ordered oblique columnar () phase, similar to a recent report on C14PhBA. The two main driving forces in the formation of these two supra-molecular columnar structures were identified: One was the H-bond formation between N-H and C[double bond, length as m-dash]O groups, and the other was the micro-phase separation between the bisamide cores and the alkyl chains. With increasing the length of alkyl tails, the isotropization temperature decreased, while the disordering temperature of the alkyl tails increased. The 2D lattice structures perpendicular to the columnar axis also increasingly deviated from the pseudo-hexagonal packing with increasing the alkyl tail length. However, the alkyl tail length did not have a significant influence on the packing along the columnar axis direction. Utilizing polarized optical microscopy, the phase identifications were also supported by the observation of texture changes and molecular arrangements inside of the micro-sized domains.

We demonstrate here a novel synthetic approach towards micron-sized poly(methyl methacrylate) particles encapsulated with smectic liquid crystals (LC) via emulsion polymerization using a diffusion-controlled swelling method. The effects of different emulsifiers, seed particles, crosslinker content, LC content and polymerization temperatures on LC capsules’ size and shape were studied to obtain the optimal conditions. The results revealed that polystyrene particles were better seed particles than poly(butyl acrylate) seed particles, yet they need more time to achieve Ostwald ripening. By introducing a high amount of crosslinking agent, the LCs can be fully encapsulated without any leakage, while the capsules’ shape changed from spheres to half-spheres when the LC loading in the starting material before polymerization was higher than 30%. The capsule size is about 2 to 10 microns with a broad distribution, as characterized by scanning electron microscopy and polarized optical microscopy. The LC capsules can be fractionated by centrifugation, and narrowly distributed capsules were obtained. The properties of the LC capsules were studied by differential scanning calorimetry, and it revealed that the LC content in the capsules was higher than the initial content in the emulsion.

Vinylidenefluoride (VDF) has been homopolymerized and copolymerized with perfluoro-n-propylvinylether (PPVE) using bis(perfluoro-2-n-propoxyethyl)diacyl peroxide (BPPP) as the initiator in CF 2 ClCFCl 2 . The polymers obtained were characterized with 19 F NMR and 1 H NMR spectroscopy, DSC and TGA. The 19 F NMR spectra were used to determine the polymer microstructures and end groups. Both PVDF and poly(VDF–PPVE) were terminated on both chain ends by CF 3 CF 2 CF 2 OCF(CF 3 )∼ arising from the decomposition of the initiator. The concentration of end groups was used to assess the molecular weight of the polymers. Using the Fine–Ross method, the reactivity ratios of both monomers were determined ( r VDF ∼ 1.06, r PPVE ∼ 0). The T g of poly(PPVE) (−10.3 °C) was determined using the T g s of VDF/PPVE copolymers with different compositions and the Flory–Fox equation. A new method to produce a modified PVDF or VDF copolymer for powder coatings with higher thermal stability was also developed.

The polymer surface relaxation in thin films has been a long debating issue. We report a new method on studying surface relaxation behaviors of polymer thin films on a solid substrate. This method involved utilizing a rubbed polyimide surface with a pretilting angle in a liquid crystalline cell. Due to the surface alignment, the liquid crystals were aligned along the rubbing direction. During heating the liquid crystalline cell, we continuously monitored the change of orientation of the liquid crystals. It is understood that at a temperature where the orientation of liquid crystal is lost, the surface relaxation on the glass substrate takes place to lose the polyimide surface orientation. It was found that the relaxation temperature at which the liquid crystals lose their orientation depends on the film thickness of the polyimide. A quantitative linear relationship between the relaxation temperature and reciprocal of the film thickness can be observed. Furthermore, different topologies of the rubbed and relaxed thin films were amplified using the polyethylene decoration method and observed using atomic force microscopy.

Chirality transfer (or amplification) in soft materials is an important topic for understanding how chiral assemblies develop from the atomic level to macroscopic objects. This is an interdisciplinary area which is critically associated with the evolution from asymmetric chemistry to asymmetric physics, and, more specifically, in biomaterials, liquid crystals, and polymers. In this review, we discuss our recent studies on the conditions for chirality transfer across different length scales. We observed that the formation of helical structures in different length scales is a typical process in chirality transfer. This is illustrated by a series of nonracemic chiral main-chain liquid crystalline (LC) polyesters, PETs(R*-n). The polymers contained a different number of methylene units in the chain backbone (from 7 to 11). All of the PETs(R*-n) macroscopically exhibited an LC chiral smectic C (SC*) phase, a chiral smectic A (SA*) phase, and a twist grain boundary smectic A (TGBA*) phase with increasing temper...

It is known that in photovoltaic applications, columnar discotic liquid crystal (LC) phases of conjugated compounds are useful to align the molecules for improving their charge mobilities. However, conjugated compounds are usually either crystalline or amorphous. For compounds to form columnar discotic LC phases, specific molecular design is required for their ordered structural packing. In our recent report, a series of conjugated compounds, 6,7,15,16-tetrakis(alkylthio)quinoxalino-[2′,3′:9,10]-phenanthro[4,5-abc]phenazine (TQPP-[SCn]4) (n = 6, 8, 10 and 12), which display p-channel characteristics, were synthesized and characterized. This series of compounds was crystalline and did not exhibit LC behavior (S. Leng, B. Wex, L. H. Chan, M. J. Graham, S. Jin, A. J. Jing, K.-U. Jeong, R. M. Van Horn, B. Sun, M. Zhu, B. R. Kaafarani and S. Z. D. Cheng, J. Phys. Chem. B, 2009, 113, 5403–5411). In order to create a columnar LC phase with the lowest free energy within a broad applicable temperature region, we specifically designed and synthesized several series of electron-deficient phenazine derivatives to disrupt the molecular crystal packing and force the compounds to enter the columnar LC phase. These phenazine derivatives were designed to control the fused rigid ring size and shape as well as the location, lengths, and chemical structures of their flexible tails. These series include a series of 2,11-bis(1-methylethyl)-6,7,15,16-tetrakis(alkoxy)quinoxalino[2′,3′:9,10]phenanthro-[4,5-abc]-phenazines (TQPP-[t-Bu]2-[OR(B)]4), a series of 2,13-bis(1-methylethyl)-7,8,18,19-tetrakis(alkoxy)pyrazino[2,3-i]pyrazino[2″,3″:6′,7′]quinoxalino[2′,3′:9,10]phenanthro[4,5-abc]-phenazines (TPPQPP-[t-Bu]2-[OR(B)]4), and a series of 3,4,11,12,19,20-hexaalkoxy-2,5,7,8,10,13,15,16,18,21,23,24-dodecaazatri-anthracenes (HDATAN-[OR]6), where R is the alkyl chain in the substituents and B represents that they are branched structures. The different phase structures and transition behaviors of these series of compounds were studied, and based on the experimental results, we can conclude that tailoring the alkyl tail size, the core size, and the core shape leads to a promising way to design molecules that exhibit the columnar LC phase. In particular, changes in alkyl tail architecture affect the phase behaviors more significantly than changes in its length.

Spherical micelles of a series of poly(styrene-block-(2,5-bis[4-methoxyphenyl]oxycarbonyl)styrene) (PS-b-PMPCS) rod-coil diblock copolymers in a selective solvent can organize into large mono-layered films with a well-ordered hexagonal packing of the spheres after solvent evaporation. Organized domains in the spherical micelle film were observed by transmission electron microscopy (TEM) and atomic force microscopy (AFM). The core-shell structure of the spherical micelle remained after solvent evaporation. The micelle diameter in the ordered film as observed by TEM and AFM agree. The size of the spherical micelles can be controlled by the length of PMPCS when the length of the PS is fixed. The sphere diameters were varied from several tens of nanometers to more than one hundred nanometers. Solutions of smaller micelle spheres formed less ordered films than those from larger micelle particles. Additionally, monolayer films of cylindrical worm-like micelles were also prepared. Those cylindrical micelles were observed to be end-capped by spherical micelles. The monolayer micelle film from the largest spherical micelles appeared red when observed in optical microscopy in the reflection mode. A broad adsorption peak with a maximum adsorption wavelength of 545 nm was observed via UV–Vis spectroscopy.

A series of 2,2′-disubstituted-4,4′-dihydroxybiphenyl monomers was prepared from 3,4,5-tris(n-alkoxy)benzyl chlorides (n = 5, 6, 8, 10, 12) and tetramethylammonium salt of 4,4′-dihydroxydiphenic acid, which was synthesized from two different 5-step routes. 2,2′-Bis(trifluoromethyl)-4,4′-biphenyldicarboxylic acid was synthesized via 5-step route. A series of aromatic polyesters containing multiple alkyl side chains was prepared from the 2,2′-disubstituted-4,4′-dihydroxybiphenyl monomers and 2,2′-bis(trifluoromethyl)-4,4′-biphenyldicarboxylic acid using diisopropylcarbodiimide as a dehydrating agent and 4-(dimethylamino)pyridinium 4-toluenesulfonate as a catalyst at room temperature. Their thermal and solution properties were measured and compared with the polyester without multiple alkyl side chains. The polyesters displayed better solubility in common solvents such as chlorinated solvents and THF but lower thermal stability than the polyester without multiple alkyl side chains. The intrinsic viscosities of the polyesters ranged from 0.68 to 2.53 dL/g and their number-average molecular weights ranged from 19,300 to 61,400. Polyesters containing C5–10 side chains were amorphous while the two polyesters containing C12 side chains crystallized at −27 and −31 °C, respectively. The thermal stability of the polyesters decreased as a result of alkyl side chains. The films of polyesters were opaque, indicating that the aromatic backbones and aliphatic side chains underwent phase separation.

A main-chain nonracemic chiral liquid crystalline (LC) polyester was synthesized using an A−B type condensation reaction of a chiral monomer, R-(−)4‘-{ω-[2-(p-hydroxy-o-nitrophenyloxy)-1-propyloxy]-1-heptyloxy}-4-biphenylcarboxylic acid, and was abbreviated as PET(R*-7). Wide-angle X-ray diffraction (WAXD) experiments combined with differential scanning calorimetry measurements revealed multiple phase transitions including a chiral twist grain boundary A (TGBA*) phase, a chiral smectic A (SmA*) phase, a chiral smectic C (SmC*) phase, and a highly ordered monoclinic crystalline (KM) phase with decreasing temperature. Flat-elongated and right-handed double-twisted helical single crystals were grown thermotropically in the smectic LC states. Both crystal types possessed the identical monoclinic unit cell: a = 1.04 nm, b = 0.46 nm, c = 5.59 nm, α = β = 90°, and γ = 84.2° based on the WAXD and selected area electron diffraction results. Uniaxial elongation of centimeter-sized films (along the xz-plane in a th...

Two series of diamine monomers, i.e., 4-[3,4,5-tris( n -alkan-1-yloxy)benzyl]-3,5-diaminobenzoate and 2,2′-bis{4-[3,4,5-tris( n -alkan-1-yloxy)benzoate]}-4,4′-biphenyldiamines containing multiple alkyl side chains, were synthesized in which the length of the alkyl side chains was varied from 5 to 18 ethylene units. Polyetherimides (PEIs) were prepared from these two diamines and bis[4-(3,4-dicarboxyphenoxy)phenyl]propane dianhydrides (BisADA) using a one-step method in 1-chloronaphthalene. All the polymers possessed good solubility in chlorinated solvents. The high-molecular weight PEIs could be solution cast into transparent, tough films. The polymers containing the side chains which were at least 16 methylene units could be crystallized. The melting points of the crystals increased as the length of the side chains increased. The glass transition temperatures ( T g s) of the PEIs decreased as the length of the side chains increased due to an internal plasticizing effect of the alkyl side chains. The PEIs containing multiple alkyl side chains showed excellent drawability with much higher elongations but lower tensile strengths and moduli compared with the commercial PEI, Ultem ® 1000. The film's in-plane refractive index parallel to the drawing direction ( n // ) increased and its in-plane refractive index perpendicular to the drawing direction ( n ⊥ ) decreased during drawing mainly due to the orientation of main chains in the drawing direction. The film's in-plane birefringence increased with the drawing ratios.

A series of diamine monomers, i.e., 2,2‘-bis{4-[3,4,5-tris(n-alkan-1-yloxy)benzoate]}-4,4‘-biphenyldiamines containing multiple alkyl side chains, were synthesized in which the length of the alkyl ...

We have investigated the self-assembly behavior of an amphiphilic diblock copolymer, polystyrene-block-poly(ethylene oxide) (PS-b-PEO), in N,N-dimethylformamide (DMF)/water and DMF/acetonitrile. In...

5,15-Bis(4-aminophenyl)-10,20-diphenylporphyrin ( trans -DATPP) was synthesized via the condensation of meso -(4-nitrophenyl)dipyrromethane and benzaldehyde. The further reaction with zinc acetylacetonate hydrate afforded zinc 5,15-bis(4-aminophenyl)-10,20-diphenylporphyrin ( trans -ZnDATPP). A series of soluble polyimides based on trans -DATPP or trans -ZnDATPP, 2,2′-bis(trifluoromethyl)-4,4′-diaminobiphenyl (PFMB) and 4,4′-hexafluoroisopropylidenediphthalic anhydride (6FDA) at various ratios was then prepared. Some physical properties of these polyimides were measured. It was found that every polyimide containing either trans -DATPP or trans -ZnDATPP had higher viscosity than the polyimide without porphyrin unit. Furthermore, the polyimides with trans -ZnDATPP showed lower viscosity than the ones without trans -ZnDATPP at approximately the same porphyrin content. Glass transition temperatures ( T g s) of polyimides containing trans -ZnDATPP were higher than polyimides containing trans -DATPP, and both were higher than polyimide without porphyrin. Steady state fluorescence spectroscopy of these polymers revealed that the quantum yield of polymers increased with higher content of free base porphyrin in the polymer chain. Time-correlated single photon counting experiments indicated these polyimides could be used in photonic applications.

Two new asymmetric odd-numbered main-chain liquid crystalline (LC) polyesters (BPE-Cn) were synthesized through the condensation polymerization of A–B type asymmetric α,ω-carboxylic acid–hydroxyl terminated monomers with odd-numbers of methylene units in the spacers (BPCA-Cn-PmOH, where n=7 and 9). The phase behaviors and structures of these odd-numbered BPE-Cn samples were characterized using the combined techniques of differential scanning calorimetry (DSC), wide angle X-ray diffraction (WAXD), selected area electron diffraction (SAED) and polarized light microscopy (PLM). One-dimensional (1D) powder WAXD results at different temperatures combined with DSC results revealed that during cooling these two polyesters enter a low-ordered LC phase before developing a crystalline phase at lower temperatures. Based on 2D WAXD of oriented fiber patterns, the low ordered LC phase of odd-numbered BPE-Cn was identified to be a smectic A (SmA) phase, which was constructed by each chemical repeating unit along the fiber drawn direction. The crystalline structures were determined to be monoclinic unit cells (KM). However, BPE-C7 possessed a γ=87°, while BPE-C9 had a β=100°. These crystalline structure identifications were also confirmed by SAED from single crystals. Two-chain packing models of the KM phases with four chemical repeating units were proposed on the basis of the experimental diffraction patterns. The different structures were attributed to the interplay between the mesogenic group ordering propensity and the chain constraints dictated by the methylene spacer and the meta-linkage at the end of mesogen. In the ordered phases of these two odd-numbered BPE-Cn polyesters, aromatic mesogenic groups are more or less parallel to each other along the chain with small angles of deviation from the c-axis of the crystal lattice, different from those large zigzag conformation structures in even-numbered BPE-Cn crystals. Crystallographic calculations of these two unit cell structures indicated that the neighboring chains in the crystals are translated along the c-axis (in the case of BPE-C9) or twisted away from the b-axis (in the case of BPE-C7) in order to incorporate both of the bend attributed to the odd-numbered methylene spacers and of the configurational meta-linkage at the end of mesogens. The simulated diffractions based on these calculations qualitatively agreed with the experimental observations. The phase identifications were also supported by the observed texture changes in PLM.

A series of newly designed polyimides, composed of aromatic polyimide backbones and methylene side chains with terminal 4-cyanobiphenyl groups, were synthesized based on the polycondensation of 3,3′,4,4′-biphenyl tetracarboxylic dianhydride (BPDA) with 2,2′-bis{ω-[4-(4-cyanophenyl)phenyoxy- n -alkoxycarbonyl]}-4,4′-biphenyl diamine ( n CBBP, where n is the number of methylene units in the side chains). We report our structural and morphological studies on this series of BPDA– n CBBP, which possesses n =7, 9, and 11 methylene units in the side chains. For these three polyimides, a nematic (N) phase was first formed at high-temperatures during cooling from the isotropic melt. The transition temperatures and enthalpies were cooling-rate independent as observed in differential scanning calorimetry. This N phase was further confirmed by the results of wide angle X-ray diffraction (WAXD) and polarized light microscopic experiments. At lower temperatures, ordered structures were formed. It was surprising that in the cases of BPDA– n CBBP ( n =7 and 9), triclinic lattices were observed; while in the case of BPDA-11CBBP, a hexagonal lattice was evident, as determined by 2D WAXD experiments. This indicated that by increasing the number of methylene units in the LC side chains, the individual chains (base unit) used in constructing these supra-molecular structures changed their packing symmetry. Namely, when the number of methylene units in the side chains was relatively low (i.e. the length is short), the individual chains were packed into a ribbon-like structure. However, when the side chain length is long enough, the individual chains exhibit cylindrical symmetry. Regardless of the lattice formed by the supra-molecular structures, they are all on the nanometer length scale.

Previously, we synthesized a series of symmetrically tapered 1,4‐bis[3,4,5‐tris(alkan‐1‐yloxy)benzamido] benzene bisamides (CnPhBA, where n is the number of carbon atoms in the alkyl chains, n=10, 12, 14, and 16). These bisamides consist of a rigid aromatic core with three flexible alkyl chains at each end of the core. It was found that all of these CnPhBA bisamides formed a highly ordered oblique columnar (ΦOK) phase and a low‐ordered oblique columnar (ΦOB) phase.[1,2] To study the dependence of structure on alkyl chain length in this series of symmetrically tapered bisamides, we focus on the structural and phase transitions of CnPhBA (n=6 and 8) via differential scanning calorimetry, one‐dimensional (1D) and 2D wide angle X‐ray diffraction (WAXD) and Fourier transform infrared spectroscopy. Structural evolutions and phase identifications were also supported by texture changes observed by polarized optical microscopy. It was interesting that there was only one ordered structure in C6PhBA which contains t...

To understand the formation mechanism of helical supramolecular structures in the smectic C (SmC) liquid crystalline (LC) phase of BPCA-Cn-PmOH (n is the number of methylene units, n = 6−10) (see: Jeong, K.-U.; Jin, S.; Ge, J. J.; Knapp, B. S.; Graham, M. J.; Ruan, J.; Guo, M.; Xiong, H.; Harris, F. W.; Cheng, S. Z. D. Chem. Mater. 2005, 17, 2852), a series of newly designed achiral C6 4-biphenyl carboxylic acid compounds was synthesized, of which all of them have six methylene units (n = 6). To recognize the importance of hydrogen (H)-bonding between hydroxyl groups and the small kink at the end of the phenyl groups, the hydroxyl group at the meta-position of phenyl groups in BPCA-C6-PmOH was first moved to the para-position to become BPCA-C6-PpOH, and then changed to a methoxy group to become BPCA-C6-PmOH3. BPCA-C6-P, having no functional groups on the phenyl groups, was also synthesized. Finally, one more compound was synthesized to disrupt the formation of the H-bonded head-to-head dimers by replacin...

A series of new asymmetric bent main-chain liquid crystalline (LC) polyesters (BPE-Cn) were synthesized through the condensation polymerization of A−B type asymmetric α,ω-carboxylic acid−hydroxyl-terminated monomers containing different even numbers of methylene spacers (BPCA-Cn-PmOH, where n = 6, 8, and 10). Differential scanning calorimetry results showed three phase transition processes in this series of BPE-Cn samples. The phase change with the lowest transition temperature is cooling rate dependent, while the two higher temperature transitions are cooling rate independent. One-dimensional (1D) powder wide-angle X-ray diffraction (WAXD) results at different temperatures revealed that during cooling this series of polymers exhibits a low-ordered LC phase and a highly ordered smectic crystal phase before developing a crystalline phase at lower temperatures. The phase structures and symmetry were identified by 2D WAXD and selected area electron diffraction (SAED). On the basis of 2D fiber WAXD patterns, ...

A series of achiral 4-biphenyl carboxylic acid compounds (BPCA-Cn-PmOH) connected with alkoxyl chains having various carbon numbers (n = 6−10) and terminated by phenyl groups with meta-positioned hydroxyl groups was synthesized. Different phase structures including nematic, smectic A (SmA), smectic C (SmC), and highly ordered smectic liquid-crystalline phases along with crystalline phases were identified based on wide-angle X-ray diffraction and electron diffraction experiments. It was found via infrared spectroscopy that the hydrogen (H)-bonds were formed between the carboxylic acids to construct head-to-head dimers as the building blocks for these ordered structural formations. H-bonds formed via the meta-positioned hydroxyl groups also played an important role in forming ordered layers in these structures. The morphology of this series of BPCA-Cn-PmOH as observed under polarized light microscopy showed an oily streak (cylinder) texture with Myelin-figure in the SmA phase. When temperature cools to ente...

A new method has been developed to prepare smart microgels that consist of well-defined temperature-sensitive cores with pH-sensitive shells. The microgels were obtained directly from aqueous graft copolymerization of N-isopropylacrylamide and N,N'-methylenebisacrylamide from water-soluble polymers containing amino groups such as poly(ethyleneimine) and chitosan. The gel diameters ranged from 300 to 400 nm with narrow size distribution. The unique core-shell nanostructures exhibited tuneable responses to pH and temperature.

The AB and AB2 quinoxaline monomers 2-(4-hydroxyphenyl)-3-phenyl-6-fluoroquinoxaline and 3-(4-hydroxyphenyl)-2-phenyl-6-fluoroquinoxaline (HPFQ) and 2,3-bis(4-hydroxyphenyl)-6-fluoroquinoxaline (BH...

A series of extended 6-substituted quinoxaline AB monomer mixtures, 2-(4-fluorophenyl)-3-[4-(4-hydroxyphenoxy)phenyl]-6-substituted quinoxaline and 3-(4-fluorophenyl)-2-[4-(4-hydroxyphenoxy)phenyl]-6-substituted quinoxaline, were prepared and polymerized to afford phenylquinoxaline oligomers. High-molecular-weight polymers could not be obtained because of the formation of cyclic oligomers. On the basis of matrix-assisted laser desorption/ionization time-of-flight analysis and molecular modeling results, the formation of a cyclic dimer could be a favorable process resulting in low-molecular-weight oligomers. They were completely soluble and amorphous, with glass-transition temperatures varying from 165 to 266°C, and they had thermooxidative stability, with samples displaying 5% weight loss temperatures of 419-511°C in nitrogen. The thermal properties of the monomers and resultant polymers dramatically depended on the polarity of the substituents. The monomers and resultant oligomers displayed high fluorescence in tetrahydrofuran solutions and N-methyl-2-pyrrolidinone solutions, respectively.

The primary objective of this research was the development of an efficient synthetic route for a previously prepared self-polymerizable PPQ monomer mixture, 2-(4-hydroxyphenyl)-3-phenyl-6-fluoroquinoxaline and 3-(4-hydroxyphenyl)-2-phenyl-6-fluoroquinoxaline. Thus, the intermediate, 4-hydroxybenzil, was synthesized in good yield, starting from phenol with phenylacetyl chloride, followed by oxidation. The other intermediate, 4-fluoro-1,2-phenylenediamine, was also less costly synthesized, starting from 2,4-difluoronitrobenzene with ammonium hydroxide, followed by reduction, giving excellent yield. The overall monomer yield was superior to previous reports. Another research objective involved preparation of various monomer mixtures that could be synthesized even less costly, and attempts on polymerization could generate the same structure of PPQ from an original monomer mixture. Thus, the monomer mixture that had switched functional groups from the original one, 2-(4-fluorophenyl)-3-phenyl-6-hydroxyquinoxaline and 3-(4-fluorophenyl)-2-phenyl-6-hydroxyquinoxaline, was prepared. Various monomers with different functional groups attached on the 6-position of the quinoxaline ring, such as chloro- and nitro-substituted monomers instead of fluoro-substituted ones, were also prepared. Several attempts to build up high molecular weights were not successful. In the case of the switched monomer mixture, weaker nucleophility and less activation on the fluorine atom were to be the reason in the switched monomer. In the cases of chloro- and nitro-substituted monomers, poorer leaving power and side reactions were to be the reasons.

A self-polymerizable AB2 monomer, 2,3-bis(4-hydroxyphenyl)-6-fluoroquinoxaline, and an A2B monomer, 2,3-bis(4-fluorophenyl)-6-(4-hydroxyphenoxy)quinoxaline, were prepared and polymerized to afford phenol-terminated and aryl fluoride terminated, hyperbranched polyphenylquinoxalines (HPPQs), respectively. MALDI−TOF analysis showed that intramolecular cyclization was a dominant process for the low molecular weight portion during the polymerizations. After isolation and complete dryness, the phenol-terminated HPPQ 1 was only soluble in strong organic acids, while the aryl fluoride terminated HPPQ 2 was soluble in most common organic solvents. HPPQ 1 was treated with allyl bromide to afford an allyl ether terminated HPPQ 3, which was also soluble in most organic solvents. Intrinsic viscosity measurements and SEC analysis indicated that HPPQ 2 had a much higher Mw and a much broader molecular weight distribution (PDI ∼ 60) than HPPQ 1 and HPPQ 3 (PDI ∼ 4). The results also suggested that HPPQ 1 formed aggregate...

Highly oriented, large area continuous composite nanofiber sheets made from surface-oxidized multiwalled carbon nanotubes (MWNTs) and polyacrylonitrile (PAN) were successfully developed using electrospinning. The preferred orientation of surface-oxidized MWNTs along the fiber axis was determined with transmission electron microscopy and electron diffraction. The surface morphology and height profile of the composite nanofibers were also investigated using an atomic force microscope in tapping mode. For the first time, it was observed that the orientation of the carbon nanotubes within the nanofibers was much higher than that of the PAN polymer crystal matrix as detected by two-dimensional wide-angle X-ray diffraction experiments. This suggests that not only surface tension and jet elongation but also the slow relaxation of the carbon nanotubes in the nanofibers are determining factors in the orientation of carbon nanotubes. The extensive fine absorption structure detected via UV/vis spectroscopy indicated that charge-transfer complexes formed between the surface-oxidized nanotubes and negatively charged (-CN[triple bond]N:) functional groups in PAN during electrospinning, leading to a strong interfacial bonding between the nanotubes and surrounding polymer chains. As a result of the highly anisotropic orientation and the formation of complexes, the composite nanofiber sheets possessed enhanced electrical conductivity, mechanical properties, thermal deformation temperature, thermal stability, and dimensional stability. The electrical conductivity of the PAN/MWNT composite nanofibers containing 20 wt % nanotubes was enhanced to approximately 1 S/cm. The tensile modulus values of the compressed composite nanofiber sheets were improved significantly to 10.9 and 14.5 GPa along the fiber winding direction at the MWNT loading of 10 and 20 wt %, respectively. The thermal deformation temperature increased with increased MWNT loading. The thermal expansion coefficient of the composite nanofiber sheets was also reduced by more than an order of magnitude to 13 x 10(-6)/ degrees C along the axis of aligned nanofibers containing 20 wt % MWNTs.

A new method has been developed to prepare smart polymeric microgels that consist of well-defined temperature-sensitive cores with pH-sensitive shells. The microgels were obtained directly from aqueous graft copolymerizations of N-isopropylacrylamide and N,N-methylenebisacrylamide from water-soluble polymers containing amino groups such as poly(ethyleneimine) and chitosan. The gel diameters ranged from 300 to 400 nm. The unique core-shell nanostructures, which had narrow size distributions, exhibited tuneable responses to pH and temperature.

A synthetic route to fused bisphenazine compounds has been developed. Thus, 2,7-di-tert-butyl-quinoxalino[2‘,3‘,9,10]phenanthro[4,5-abc]phenazine-6,7,15,16-tetraalkoxy compounds have been synthesized in good yields. The structures of these new compounds were ascertained by nuclear magnetic resonance (NMR) and mass spectroscopy. Differential scanning calorimetry (DSC), polarized light microscopy (PLM), and wide-angle X-ray diffraction (WAXD) studies showed that some of these planar molecules display liquid crystalline phases at elevated temperatures. WAXD analysis also indicated that the molecules undergo π−π stacking in the liquid crystalline phase. Differential pulse voltammetry (DPV) showed that the compounds undergo two reduction processes. Thus, it is speculated that the materials have potential as electron transporting materials in electronic devices such as organic photovoltaic or light-emitting diodes.

4-Chloro-2,5-bis(4-fluorophenyl)oxazole monomer has successfully been synthesized using cyclization reaction of 4-fluorobenzoyl cyanide with 4-fluorobenzaldehyde. This monomer was converted to poly(aryl ether)s by nucleophilic substitution of the fluorine atoms on the benzene rings of oxazole monomer with bisphenol A. The influence of the reaction time on the molecular weight had been investigated. The polymers were identified by FT-IR, 1 H-NMR and TGA. The products exhibited weight-average molar masses up to 2.81 x 10 4 g mol -1 in GPC. These poly(aryl ether)s showed very high thermal stability up to 363 °C for 5 % weight loss in TGA under N 2 .

Self-assembled “supra-molecular” liquid-crystalline phases were investigated in one of a series of symmetrically tapered bisamides based on an amide core of 1,2-bis[3,4,5-tris(alkan-1-yloxy)benzamido]benzene and three alkyl tails on each side of the core. One of this series of bisamides having 14 carbon atoms in each tail (abbreviated as C14PhBA) served as an example in this study. Differential scanning calorimetry thermal diagrams showed two main phase transition processes in C14PhBA. Wide-angle X-ray diffraction results revealed that the high-temperature phase transition is between the isotropic melt (I) and a 2D low-ordered oblique columnar phase (I ↔ ΦOB). The low-temperature phase transition was attributed to the transition between a highly ordered, oblique columnar (ΦOK) phase and the ΦOB phase. Supra-molecular columns were directly visualized using transmission electron microscopy and atomic force microscopy. The formation of these supra-molecular structures is critically dependent upon the constru...

A phenylquinoxaline (PQ) AB monomer mixture was treated with monofunctional and difunctional end-capping agents and with and without a coupling agent to afford phenylethynyl-terminated linear PQ oligomers. The resulting PQ oligomers were soluble in common organic solvents and had intrinsic viscosities (IVs) of 0.21-0.30 dL/g. The glass-transition temperature (T g ) of the diphenylethynyl-end-capped PQ oligomer on both sides increased the most, from 215 °C (before curing) to 251 °C (after curing). The PQ AB 2 monomer, which acted as both a coupling agent and a monomer for the hyperbranched polymer, was treated with an AB monomer and end-capping agents to afford phenylethynyl-terminated hyperbranched polyphenylquinoxalines (PPQs). They were also soluble in common organic solvents, had IVs of 1.00-1.65 dL/g and T g 's of 251-253 °C, and underwent exothermic cure with maxima around 412-442 °C. The T g 's of the cured hyperbranched PPQs ranged from 258 to 261 °C, depending on the number of phenylethynyl groups on the surface. After further curing, they displayed a T g of 316 °C in one sample and turned into a fully crosslinked network. The dynamic melt viscosities of a linear oligomer (IV = 0.21 dL/g), a hyperbranched sample (IV = 1.00 dL/g), and a linear reference PPQ (IV = 1.29 dL/g) were compared with respect to the processing temperature. The PQ oligomer and hyperbranched PPQ had low melt viscosities.

Extended self-polymerizable poly(phenylquinoxaline) monomer mixtures {i.e.,2-[4-(4-hydroxyphenoxy)phenyl]-3-phenyl-6-chloroquinoxaline and 3-[4-(4-hydroxy phenoxy)phenyl]-2-phenyl-6-chloroquinoxaline, 2-[4-(4-hydroxyphenoxy)phenyl]-3-phenyl-6-fluoroquinoxaline and 3-[4-(4-hydroxyphenoxy)phenyl]-2-phenyl-6-fluoroquinoxaline, and 2-(4-fluorophenyl)-3-phenyl-6-(4-hydroxyphenoxy)quinoxaline and 3-(4-fluorophenyl)-2-phenyl-6-(4-hydroxyphenoxy)quinoxaline} more flexible and nucleophilic than a previously reported monomer mixture [i.e., 3-(4-hydroxyphenyl)-2-phenyl-6-fluoroquinoxaline and 2-(4-hydroxyphenyl)-3-phenyl-6-fluoroquinoxaline] were synthesized. The monomer mixtures were then polymerized into high-molecular-weight polymers. A sample was obtained, through a chlorine displacement reaction, that was a semicrystalline polymer with an intrinsic viscosity of 1.11 dL/g in m-cresol at 30 ± 0.1 °C and two melting temperatures at 339 and 377 °C in the first differential scanning calorimetry scan. There was a melting temperature at 328 °C without a detectable glass-transition temperature (Tg) when the sample was subjected to a second differential scanning calorimetry scan. The samples from fluorine displacement reactions were completely amorphous polymers. They had intrinsic viscosities of 0.53–0.90 dL/g in m-cresol at 30 ± 0.1 °C and Tg's of 220–224 °C. The polymer samples from fluorine displacement reactions were evaluated with gel permeation chromatography and matrix-assisted laser desorption/ionization time-of-flight analyses, which monitored the existence of certain amounts of cyclic oligomers. The thin films of the polymers had room-temperature tensile strengths of 97–113 MPa, room-temperature Young's moduli of 2.30–2.35 GPa, and room-temperature elongations at break of 40–150%. The melt viscosity decreased from 107 to less than 104 Pa s at 310 °C as the frequency was increased from 10−2 to 102 rad/s. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 78–91, 2005

The series of new bis(naphthalic anhydrides) was prepared through Diels-Alder cycloaddition. The Diels-Alder cycloaddition was used as a synthetic route to new phenylated monomers as well as to polymers. All polymers synthesized revealed to be soluble in a wide range of organic solvents such as toluene,THF, chloroform, and displayed high thermostability. Therefore, they can be processed easily and are promising candidates for advanced coating systems as well as for electrooptical applications.

Ultraviolet (UV) polymerizable discotic liquid-crystalline (DLC) molecules (2,3,6,7,10,11-hexakis(4′-acryloy-m-alkyloxybenzoyoxy)triphenylene [HAHBT-m, where m was the number of methylene units, and here m = 6 (HAHBT-6)]) were assembled to form a negative retardation film with an oblique optical axis on a specifically designed rubbing-aligned polyimide layer surface [6FDA-11CBBP (where 11 is the number of methylene units in the side chains)]. The side chains of this polyimide were terminated by cyanobiphenyl groups. Surface-enhanced Raman scattering (SERS) and optical second harmonic generation results showed that rubbing caused a surface structural re-arrangement in the alignment layer resulting in a negative pre-tilt angle (θs) of –8.5° (which was in the direction opposite to the rubbing direction). The molecular topology at the rubbed surface was governed by a stable fold-like bent structure of the cyanobiphenyl side chains, in which the CN groups preferentially pointed down towards the surface. When the DLC molecules were deposited onto the alignment surface and polymerized via UV irradiation to generate a new optical film, an oblique optical axis with an average tilt angle of –18.6° with respect to the film normal was detected using ellipsometric measurements. This tilted optical axis was developed by the DLC molecules being wedged on top of the cyanobiphenyl groups when in the bent conformation. Furthermore, the tilt angle difference between the θs at the alignment surface and at the air interface of the DLC molecules was attributed to a splay deformation of the DLC molecules along the film surface normal. Optical modeling has also confirmed our experimental observations.

Two new extended self-polymerizable AB monomers, N-(4-fluorobenzoyl)-4-amino-4'-hydroxydiphenylether and N-(4-fluorobenzoyl)-4-amino-4'-hydroxybiphenyl, were prepared. The monomers were homopolymerized and copolymerized to high-molecular-weight, linear poly(arylether amides) in N-methylpyrrolidone (NMP)/toluene in the presence of potassium carbonate at elevated temperature. The polymers retained NMP up to 200 °C. Samples containing small amounts of the solvent (5-10 wt %) were soluble in polar aprotic solvents. However, after complete removal of the NMP, the polymers were only soluble in strong acids such as sulfuric acid and methanesulfonic acid (MSA). The polymers, which had intrinsic viscosities of 0.57-1.49 dL/g (30.1 ± 0.1 °C in MSA), were semicrystalline with melting temperatures above 400 °C. Two new self-polymerizable AB 2 amide monomers, N,N'-bis(4-fluorobenzoyl)-3,4-diamino-4'-hydroxydiphenylether and N,N'-bis(4-fluorobenzoyl)-3,5-diamino-4'-hydroxybenzophenone, were also prepared and polymerized to give a hyperbranched poly(arylether amide) and a hyperbranched poly(aryletherketone) amide. The arylfluoride-terminated, amorphous polymers had intrinsic viscosities of 0.34 and 0.24 dL/g (30.0 ± 0.1 °C in m-cresol), glass-transition temperatures of 210-269 °C, and were soluble in a wide variety of organic solvents. Matrix-assisted laser desorption/ionization time-of-flight analysis indicated that the components of the low-molecular-weight fractions contained cyclic structures.

Functional latexes with poly(methyl methacrylate) (PMMA) cores and amino‐containing, water‐soluble polymer shells were synthesized via direct graft copolymerization of methyl methacrylate from water‐soluble polymers induced by a small amount of tert‐butyl hydroperoxide (TBHP) at 80°C for 2 h. Amphiphilic graft copolymers and PMMA homopolymers were generated concurrently to form highly monodispersed latexes. The effects of water‐soluble polymer containing different amino group, reaction temperature, TBHP concentration, molecular weight of the polymer and pH of the solution on conversion and grafting efficiency of the monomer and particle size were investigated. Transmission electron microscopic images of the PMMA/poly(ethyleneimine) (PEI) and PMMA/poly(allylamine) (PAA) particles clearly show well‐defined core‐shell morphologies, where PMMA cores are coated with either PEI or PAA shell. The amino‐containing polymer shells were also confirmed with zeta‐potential measurements. Furthermore, the amino...

A nonracemic chiral main-chain liquid crystalline (LC) polyester was synthesized from (R)-(−)-4‘-{ω-[2-(p-hydroxy-o-nitrophenyloxy)-1-propyloxy]-1-undecyloxy}-4-biphenylcarboxylic acid via an A−B type condensation polymerization. The polymer was abbreviated as PET(R*-11), where 11 is the number of methylene units in the chain backbone. Other PETs(R*-n) (n = 7−11) in this series were also studied. PET(R*-11) exhibited a LC chiral smectic C (SC*), a chiral smectic A (SA*), and a twist grain boundary smectic A (TGBA*) phase with increasing temperatures as identified by differential scanning calorimetry, polarized light microscopy, and wide-angle X-ray diffraction (WAXD). Flat-elongated lamellae were observed in transmission electron microscopy (TEM) for thin-film melt crystallized samples. Its crystal structure was determined to be a monoclinic basic unit cell with a = 1.03 nm, b = 0.47 nm, c = 6.43 nm, and γ = 83° via selected area electron diffraction (SAED), and these measurements were confirmed by two-di...

A novel method has been developed to prepare amphiphilic core−shell polymer nanospheres via graft copolymerizations of methyl methacrylate (MMA) from water-soluble polymer chains containing amino g...

A main-chain nonracemic chiral liquid crystalline polymer was synthesized from (R)-(-)4'-{w-[2-(p-hydroxy-o-nitrophenyloxy)-1-propyloxy]-1-decyloxyl-4-biphenylcarboxylic acid. This polymer contained 10 methylene units in each chemical repeating unit and was abbreviated PET(R*-10). On the basis of differential scanning calorimetry, wide-angle X-ray diffraction, and polarized light microscopy experiments, chiral smectic C (S-C*) and chiral smectic A (S-A*) phases were identified. Both flat-elongated and helical lamellar crystal morphologies were observed in transmission electron microscopy. Of particular interest was the flat-elongated lamellar crystals were constructed via microtwinning of an orthorhombic cell with dimensions of a = 1.42 nm, b = 1.28 nm, and c = 3.04 nm. On the other hand, the helical lamellar crystals were exclusively left-handed, which was opposite to the right-handed helical crystals grown in PET(R*-9) and PET(R*-11) (having 9 and 11 methylene units, respectively). Note that these three polymers had identical right-handed chiral centers (R*-). Therefore, a single methylene unit difference on the polymer backbones on an atomic length scale substantially changed the chirality of the crystals in the micrometer length scale. Furthermore, aggregates of these helical crystals in PET(R*-10) did not generate banded spherulites in polarized light microscopy. Possible reasons for this change and loss of helical senses (handedness) on different length scales in chirality transferring processes were discussed.

A thermotropic liquid crystalline (LC) polyether was synthesized by condensation polymerization of 1-(4-hydroxyphenyl-2-(2-methyl-4-hydroxypheyl)ethane) and α,ω-dibromononane, and abbreviated as MBPE-9. Multiple phase transitions were found via differential scanning calorimetry (DSC) upon heating and cooling. Based on wide-angle X-ray diffraction (WAXD) and polarized light microscopy (PLM) experiments, two monotropic LC nematic (N) and smectic phases and three crystalline (orthorhombic K1, triclinic K2 and triclinic K3) phases were identified. A study on kinetics showed that only when the N phase formation rate was faster than the crystallization rate of K1 phase which directly grew from the melt, the presence of the N phase could accelerate both the overall crystallization and the linear crystal growth rates of K1 phase. In a narrow temperature region, two distinct crystal growth rates could be observed: one was directly from the isotropic melt, and another was from the N phase.

UV–Vis irradiation of bis(pyridinium salt) model compounds and poly(pyridinium salt)s in amide solvents result in dramatic changes in their UV–Vis spectra. The absorption maximum near 342 nm, characteristic of pyridinium rings, disappears, while an absorption maximum near 500 nm appears and then disappears. During this process, the solutions change from yellow to dark red to light yellow. The inherent viscosities of the poly(pyridinium salt)s also decrease dramatically under UV–Vis irradiation. Both the color changes and the viscosity decreases are unaffected by the nature of the pyridinium salt counter anion. However, they are dramatically affected by the presence of pendent substituents. Electron-withdrawing groups increase the rate at which these changes take place, while electron-donating groups retard them. It is speculated that the photodecomposition proceeds through the initial formation of radical cations. It is also speculated that the amide groups may serve as reducing agents providing electrons in the electron transfer process. Evidence for this comes from the fact that a poly(pyridinium salt) containing pendent amide groups underwent photoreduction in DMSO in marked contrast to other poly(pyridinium salt)s that are photostable in this solvent.

Alignment layers for liquid crystal cells were prepared by directional deposition of high molecular weight rigid-rod ionomers on glass and indium–tin–oxide substrates. Several deposition techniques were developed and tested. Material type, concentration, temperature, and application technique were systematically varied and the resultant alignment of the liquid crystals studied. Three different methods of applying the alignment layer were investigated: directional spray deposition, brushing, and directional deposition using a squeegee (doctor bar). The application temperature ranged from 30 to 80°C. The best results were obtained using a squeegee to perform directional deposition at temperature of less than 60°C. The alignment layers obtained in this way are robust, exhibit excellent alignment, and have pretilt angles of a few degrees.

A series of specially designed polyesters consisting of aromatic main-chain/side-chain liquid crystalline (LC) polymers for flat-panel display applications have been synthesized via polycondensation of 2,2‘-bis(trifluoromethyl)-4,4‘-biphenyldicarbonyl chloride with 2,2‘-bis{ω-[4-(4-cyanophenyl) phenyoxy]-n-alkoxycarbonyl}-4,4‘-biphenyldiol (PEFBP(n), where n is the number of methylene units in the side chains). For a PEFBP polyester of which a 4-cyanobiphenyl mesogen in each side chain is coupled with the aromatic backbone via seven methylene units, PEFBP(n=7), complicated polymorphism has been identified during its structural evolutions. On the basis of differential scanning calorimetry, wide-angle X-ray diffraction, electron diffraction (ED), polarized light, and transmission electron microscopy (TEM) experiments, it is found that this polymer possesses three triclinic crystalline (Kt1, Kt2, and Kt3) phases having the same symmetry but different unit cell dimensions, one highly ordered LC smectic phase ...

An improved, less expensive route to a high-performance poly(aryl ether phenylquinoxaline) has been developed. Thus, an isomeric mixture of self- polymerizable (A-B) quinoxaline monomers, 2-(4-hydroxyphenyl)-3-phenyl-6- chloroquinoxaline and 3-(4-hydroxyphenyl)-2-phenyl-6-chloroquinoxaline, was prepared by the condensation of 1,2-diamino-4-chlorobenzene with 4-hydroxybenzil The mixture was polymerized at 200°C in benzophenone containing potassium carbonate and a freshly prepared copper(I)chloride/quinoline catalyst mixture. The polymer obtained displayed an intrinsic viscosity of 1.53 dl/g (m-cresol at 30.0±0.1°C and a glass transition temperature of 252°C (DSC), similar to samples prepared previously from an analogous fluorine-substituted mixture.

The objective of this research was to prepare colorless photosensitive polyimides for optical applications. In the first approach to these materials two new photosensitive end-capping agents, i.e.,...