Preparation of New Hole Transport Polymers via Copolymerization of N,N ′‐Diphenyl‐N,N′‐bis(4‐alkylphenyl)benzidine (TPD) Derivatives with 1,4‐Divinylbenzene

Monomers containing N,N ′,N,N ′‐tetraphenylbenzidine (TPD) were prepared by introducing two alkyl or alkoxy substituents into the p‐position of two of the four phenyl groups in the triphenylamine unit. The monomers were copolymerized with 1,4‐divinylbenzene (DVB) in the presence of p‐toluenesulfonic acid and Lewis acids, such as SnCl₄ and BF₃. The polymerization conditions and the catalyst types showed a marked influence on yield, molecular weight and even polymer structure. ¹H NMR measurements revealed that, by using p‐toluenesulfonic acid as a catalyst, the linkage between the TPD unit and DVB occurs at the p‐position of the phenyl group and at the m‐position of the tolyl group in the TPD unit, whereas, with SnCl₄ or BF₃ catalyst, substitution occurs exclusively at the p‐position of TPD. All polymers are soluble in common organic solvents, which allows the preparation of thin films of good quality. The rigid structure of the polymeric backbone results in a high thermal stability up to 400°C. The results of ionization potential measurements and the redox behavior showed that the introduction of the TPD unit into this kind of polymer backbone does not change its electronic structure. On the basis of high electroactivity, the polymers were successfully used as hole transport layers in two‐layer electroluminescence devices.     

Thermo‐Induced Double Phase Transition Behavior of Physically Cross‐Linked Hydrogels Based on Oligo(ethylene glycol) methacrylates

Double thermosensitive clay/P(MEO₂MA‐co‐POEGMA) nanocomposite (NC) hydrogels are prepared by in situ free radical polymerization of 2‐(2‐methoxyethoxy) ethyl methacrylate (MEO₂MA) and oligo(ethylene glycol) methacrylate (OEGMA) in the presence of physical cross‐linker clay. The temperature‐induced phase transition behavior of NC hydrogels is investigated by turbidity, temperature dependent nuclear magnetic resonance, and variable temperature Fourier transform infrared spectroscopy. 2D infrared analysis is employed to study the sequential order of changes of all groups in NC hydrogels during the heating and cooling process. The obtained novel clay/P(MEO₂MA‐co‐POEGMA) NC hydrogels exhibit an unusual thermally induced multistep aggregation process and successively undergo three consecutive microstructural changes: “loose clay/polymer microaggregation ? homogeneous network structure ? dense clay/polymer macroaggregation.” Dynamic light scattering and transmission electron microscopy measurements show similar results of the NC nanogel at the same temperature regions, confirming the three consecutive microstructural changes. This new generation of thermosensitive hydrogel offers promising potential for applications as smart devices, biomedical materials, and drug carriers.

     

Size‐Dependent Isotropic/Nematic Phase Transition Behavior of Liquid Crystalline Peptide Nanowires

We present size‐tunable assemblies of peptide nanowires and study their liquid crystalline phase behavior. An aromatic peptide molecule of diphenylalanine was rapidly assembled into one‐dimensional nanowires, whose sizes were tunable according to the initial concentration of diphenylalanine in the preparing solution. The stable dispersion of peptide nanowires in an organic solvent exhibited colloidal nematic liquid crystalline phases. The liquid crystalline phase transition was governed by the repulsive electrostatic interaction among peptide nanowires as well as their shape anisotropy and polydispersity. Our work provides an interesting model system to investigate the liquid crystalline phase behaviors of a biomolecular assembly in terms of its assembled morphology and intermolecular interactions.

     

Phase Behavior of Nematic Liquid Crystal/Star‐Polymer Systems

We investigated mixed nematic liquid crystal/star‐polymer systems and derived a new model based on Freed's lattice cluster theory to describe their phase behavior. To account for the highly oriented interactions between segments, the proposed model requires an additional parameter (δε/k) related to the energy of the oriented interaction. The nematic–isotropic transition temperature of p‐ethoxy‐benzylidene‐p‐n‐butylaniline (EBBA)/star‐polystyrene systems were determined by thermo‐optical analysis technique. The proposed model gives very good agreement with experimental data.     

Phase Separation in Poly(9,9‐dioctylfluorene)/Poly(methyl methacrylate) Blends

Binary blends of the conjugated polymer poly(9,9‐dioctylfluorene) (PFO) and the insulating polymer poly(methyl methacrylate) (PMMA) phase‐separated and exhibited optical and electrical activity in light‐emitting‐diodes. The phase‐separated PFO columns were uniformly packed and situated directly on a transparent hole‐injecting contact. The length scales of lateral topographical features can be adjusted discretionarily by controlling the blend concentration and compositional ratio. The mechanism leading to the formation of lateral structures was investigated by comparing with the vertical segregation in polar conjugated polymer poly(9,9‐bis(6‐diethoxylphosphorylhexyl)fluorene) (PF‐EP) blends with PMMA, which suggested that kinetics rather than interfacial free energy acted. In such lateral phase‐separated structures, the phase‐separated PFO domains were the optically and electrically active phase. This highlighted the potential opportunity as nanoscale light source for organic optoelectronic device applications with well‐controllable properties.

     

Synthesis,Phase Behaviour and Mechanical Properties of Poly(2‐methyl‐1,3‐propanediol‐4,4′‐bibenzoate)

The synthesis and phase behaviour of PB32 is reported. The results indicate that PB32 develops a low‐ordered smectic mesophase of the type SmC_alt. The slow formation of such a mesophase allows the quenching of the isotropic melt into an amorphous state so that both amorphous glass and smectic glass can be obtained, which exhibit different glass‐transition temperatures. Mechanical tests indicate that the macromolecular chains in the mesophase of PB32 can be oriented either parallel or perpendicularly in relation to the streching direction, depending on the deformation conditions. Solid‐state ¹³C NMR spectroscopy results show that the mobility of the chains is rather similar in both phases.

     

Electrochemical and Optical Properties of Novel Poly(3‐substituted‐2,2′‐bithiophene)s

The electrochemical and optical properties of poly(3‐substituted‐2,2′‐bithiophene)s with bromo, alkyl, alkoxy and alkylthio pendants obtained by electrochemical polymerisation were investigated. As 3‐alkylthiothiophenes, 3‐alkylthio‐2,2′‐bithiophenes cannot be electropolymerised although the polymer can be successfully generated via a chemical oxidative approach. Other monomers were successfully electropolymerised to afford uniform polymer films on the anodic electrodes by adopting either Bu₄NBF₄—CH₃CN or boron trifluoride diethyl etherate (BF₃—OEt₂) as the electrolytic media. These two media exhibit contrasting effects on the film formation behaviour and optoelectronic properties in some of these polybithiophenes with different pendants. The oxidation potentials of monomers in Bu₄NBF₄—CH₃CN follow the trend: 3‐methoxy‐2,2′‐bithiophenes < 3‐octylthio‐2,2′‐bithiophenes < 2,2′‐bithiophenes < 3‐octyl‐2,2′‐bithiophenes < 3‐bromo‐2,2′‐bithiophenes while those of the polymers are poly(3‐methoxy‐2,2′‐bithiophene)s < poly(3‐octyl‐2,2′‐bithiophene)s < poly(2,2′‐bithiophene)s < poly(3‐bromo‐2,2′‐bithiophene)s. However, in BF₃—OEt₂ the trend of oxidation potentials for monomers is 3‐octylthio‐2,2′‐bithiophenes < 2,2′‐bithiophenes < 3‐bromo‐2,2′‐bithiophenes < 3‐octyl‐2,2′‐bithiophenes < 3‐methoxy‐2,2′‐bithiophenes while that for polymers is poly(3‐octyl‐2,2′‐bithiophenes) < poly(3‐methoxy‐2,2′‐bithiophenes) < poly(2,2′‐bithiophenes) < poly (3‐bromo‐2,2′‐bithiophenes). The facile and stable p‐ and n‐dopability of poly(3‐alkyl‐2,2′‐bithiophene) was also investigated.     

Effect of Rotaxane Formation on the Photophysical,Morphological, and Adhesion Properties of Poly[2,7‐(9,9‐dioctylfluorene)‐alt‐(5,5'‐bithiophene)] Main‐Chain Polyrotaxanes

In order to investigate the effect of rotaxane formation on the photophysical and morphological properties of π‐conjugated materials, a new main chain polyrotaxane was synthesized through Suzuki coupling between the inclusion complex of 5,5'‐dibromo‐2,2'‐bithiophene with randomly methylated β‐cyclodextrin and 9,9‐dioctylfluorene‐2,7‐trimethylene diborate. Due to rotaxane formation, a blue shift in the absorption spectra as well as in the fluorescence spectra was observed, while the fluorescence quantum yields and fluorescence lifetimes remained unchanged. This study demonstrates that rotaxane formation can alter the electronic and morphological properties of the threaded copolymer, which is of great interest for electronic applications.

     

Determination of Poly(4,4′‐diphenylsulfonyl terephthalamide) Crystalline Structure Via WAXD and Molecular Simulations

The crystal structure of poly(4,4′‐diphenylsulfonyl terephthalamide) (pt‐PSA) is studied by X‐ray diffraction and molecular simulation. Although the number of observed reflections is limited to warrant a precise determination of the unit cell structure and symmetry, a reasonable monoclinic unit cell is suggested with dimensions of a = 0.645 nm, b = 0.488 nm, c = 3.010 nm, and γ = 122.5°. A twofold molecule with two monomeric units forming a large zigzag conformation satisfies the X‐ray diffraction data. A layer structure is formed in the crystal phase, which is stabilized by the hydrogen bond between ? NH and ? C?O and the parallel‐displaced π–π stacking from the distortional coplanarity of the benzene rings and amide group.

     

Molecular Packing and Orientation Transition of Crystalline Poly(2,5‐dihexyloxy‐p‐phenylene)

The effect of thermal treatment on the transition of molecular packing and orientation of the semiconducting poly(2,5‐dihexyloxy‐p‐phenylene) (PPP) film is probed by the combination of in situ 2D grazing incidence X‐ray diffraction (2D GIXD) and selected area electron diffraction (SAED). The structure analysis indicates that PPP crystallizes in an orthorhombic unit cell with a = 21.20 Å, b = 3.78 Å, and c = 4.24 Å. A variation of the annealing temperature from 80 °C to 100 °C demonstrates that the worm‐like morphology in the pristine film melts and develops into nanowires. Furthermore, the molecular orientation transforms from face‐on to edge‐on via thermal annealing. Remarkably, a previously unknown metastable state of “slope” edge‐on with a tilt angle of 51.1° is observed. This orientation change arises from the heterogeneous nucleation and growth of edge‐on PPP crystal during crystallization from the melt.

     

Potentiometric Behavior of Polyampholytes Based on N,N′‐diallyl‐N,N′‐dimethylammonium Chloride and Maleamic Acid Derivatives

Strongly alternating copolymers (PalH, PalPh, PalPhBisCarb) composed of N,N′‐diallyl‐N,N′‐dimethyl‐ammonium chloride (DADMAC) and maleamic acid derivatives (MAD) are synthesized by a water‐based free radical copolymerization using 4,4‐azobis(4‐cyanovaleric acid) (V501) as the initiator. The structure of the copolymers is verified by ¹H‐NMR, elemental analysis, and thermogravimetric measurements, and the physicochemical properties are investigated by viscometric and potentiometric techniques. Potentiometric titration curves show that the acidity of the carboxylic groups strongly depends on the degree of dissociation and the ionic strength. Since all copolymers behave as polycations at low degree of dissociation, a transition from an extended chain to a coil conformation can be identified by reaching the isoelectric point (IEP).     

Synthesis and Characterisation of Side‐Chain Liquid Crystalline Poly[1‐({[(4‐cyano‐4′‐biphenyl)oxy]alkyl}oxy)‐2,3‐epoxypropane]

Summary: A new series of side‐chain liquid‐crystal polymers, the poly[1‐({[(4‐cyano‐4′‐biphenyl)oxy]alkyl}oxy)‐2,3‐epoxypropane], has been synthesized in which the spacer length is varied from 2 to 8 methylene units. The synthesis used for the chemical modification of polyepichlorohydrin (PECH) involved the phase transfer catalyzed etherification of the chloromethyl groups with sodium 4‐cyano‐4′‐biphenoxide and lithium n‐(4‐cyano‐4′‐oxybiphenyl)‐alkanoates. All the resulting polymers (except polymers 7 and 8), including that without spacer, characterized by ¹H NMR, and IR, exhibit thermotropic liquid crystalline mesomophism. The thermal behavior of the polymers has been characterized using differential scanning calorimetry (DSC) and polarized light microscopy (POM) equipped with hot‐stage. A more pronounced odd‐even effect in the clearing temperatures is observed on increasing the spacer length in which the odd members display slightly higher values, which were also dependent on the substitution degree of PECH. The flexible PECH chain assists nematic LC formation compared with other more rigid backbone polymers where a smectic phase is often encountered with the same mesogen. A comparison of the thermal properties of the cyanobiphenyl based series reported here. Polyacrylate (PA) and poly(methacrylate)‐based (PMA) SCLCPs containing 4‐cyanobiphenyl as the mesogenic unit are consistent with the general rule that increasing backbone flexibility for a given mesogenic unit and spacer length enhance the clearing temperature. This was not found from the PECH‐based series, which show the lower clearing temperature than the PMA and PA series, even though they have more flexible backbone than PA and PMA series. So the clearing temperature is not solely determined by the flexibility of the backbone.

Schlieren textures of PECHOC2‐B taken at 110 °C (cooling from isotropic phase after annealing 1 h).     

Rod‐Length Dependent Aggregation in a Series of Oligo(p‐benzamide)‐Block‐Poly(ethylene glycol) Rod‐Coil Copolymers

Summary: The synthesis of a series of rod‐coil diblock copolymers with flexible poly(ethylene oxide) chains ( = 5 000 g · mol⁻¹) and rod blocks consisting of monodisperse oligo(p‐benzamide)s is described. The formation of defined supramolecular aggregates in solution as well as the solid state has been analyzed. The length of the oligo(p‐benzamide)s has been systematically varied from n = 1 to 7 units. The influence of n on aggregation in chloroform and aqueous solution was investigated by GPC as well as UV‐vis spectroscopy. A critical aggregation length was found for chloroform (n = 5) and water (n = 4), below which no aggregation is observed under otherwise identical experimental conditions. Aggregation of the polymers in chloroform solution can be chemically reversed by the addition of PCl₅, resulting in conversion of the aromatic amides into imidoyl chlorides. Such amide‐protected block copolymers show no aggregation in NMR and GPC experiments. Imidoyl chloride formation was shown to be reversible, i.e., addition of water regenerated the oligo(p‐benzamide) blocks.

Conversion of aramide block copolymer into molecularly dissolved form using PCl₅.     

Structure and Phase Transitions of Poly(heptamethylene p,p′‐bibenzoate): Time‐Resolved Synchrotron WAXS and DSC Studies

Time‐resolved wide‐angle X‐ray scattering (WAXS), as well as differential scanning calorimetry (DSC) and polarisation microscopy studies, were applied to investigate the structure and phase transitions of poly(heptamethylene p,p′‐bibenzoate). Temperature dependencies of several structural parameters were determined. Complete transformation from an isotropic melt to a smectic phase was suggested whereas the transition from a smectic to crystalline phase is only partial (around 30%), although it takes place from the ordered SCA phase. Crystals are formed within the SCA domains with nearly the same coherent length. On the basis of the analysis of the position and the profile of the diffuse wide‐angle X‐ray scattering and mesogenic layer spacing, it was assumed that either crystallisation modifies the smectic structure, or mesophase losses its positional order because of the lack of mobility of the spacers at low temperatures.

WAXS scattering profiles corresponding to P7MB: a) cooling from the isotropic melt at 2 °C · min^?1; b) subsequent melting at 12 °C · min^?1.     

Intra‐Molecular Energy Transfer Characteristics of Novel Oligo(thienylphenyl)amine Derivatives Having a Gradient Structure

Oligo(thienylphenyl)amine (TTPA) derivatives which have different thiophene units and potential gradient molecules were synthesized. From the investigation of steady‐state absorption and emission properties and the estimation of the free energy and the energy level of the oligomers, the energy transfer efficiency of the oligomers increased with increasing thiophene units, implying that the energy transfer mainly occurs through space due to a large area overlap existing between the absorption and the emission spectra of the oligomers. Furthermore, based on the calculated Rehm‐Weller equation (ΔGen and ΔGel) and energy diagrams of the oligomers, we found that 4TTPA ( 4 ), having a 4‐unit thiophene in the backbone, showed higher energy transfer efficiency compared to that of the others.

Molecular structures of TTPA oligomers.     

Synchrotron X‐ray and DSC Studies of the Phase Behaviour of Poly(diethylene glycol p,p′‐bibenzoate)

Time‐resolved synchrotron X‐ray and DSC experiments were applied to investigate the phase behaviour of poly(diethylene glycol p,p′‐bibenzoate), PDEB. The DSC results are indicative of the formation of a smectic mesophase, previously identified as a SmCA type, which can be easily quenched down to room temperature. However, the synchrotron results show that the SmCA phase undergoes some kind of ordering or transformation at temperatures below 110 °C. Moreover, the annealing of PDEB at temperatures above T_g for sufficiently long times leads to the formation of a highly ordered structure, although very thin crystals and low crystallinities are obtained.

Scattering profiles corresponding to sample PDEB85 in a melting experiment.     

Two‐Step Smectic CA Phase Formation from Isotropic Liquid upon Supercooling in Main‐Chain Liquid‐Crystalline BB‐5(1‐Me) Polyester

The mesophase formation process of a main‐chain BB‐5(1‐Me) polyester in the supercooled isotropic‐liquid state has been studied using DSC, WAXD, and optical microscopy. The supercooled isotropic liquid follows two different SmCA formation processes. Above 85 °C, it forms the expected SmCA phase. Below, it yields a metastable SmA phase that displays a layer spacing almost twice the one of the SmCA phase. The SmA phase develops from a homogeneous nucleation followed by 3D growth and thereafter transforms to the SmCA phase. This two‐step SmCA formation involves a change in polymer chain configuration: first, the chains are folded in each two units to form the SmA phase and then they stretch to achieve the characteristic zigzag arrangement of the mesogens in the SmCA phase.

     

Photocontrol of Birefringence and In‐Plane Molecular Orientation in Copolymer Liquid Crystal Films with 4‐Methoxyazobenzene and Photo‐Cross‐Linkable Side Groups

Control of the in‐plane orientation direction in a polymethacrylate copolymer liquid crystal film substituted with 4‐methoxyazobenzene (4MAz) and 4‐methoxycinnamoyloxybiphenyl (4MCB) side groups, and control of the reversible birefringence of the resultant oriented film are described. High‐order in‐plane molecular orientation was generated by irradiating with linearly polarized (LP) 365 nm light and subsequent annealing. By adjusting the exposure dose, the reorientation direction was controlled parallel and perpendicular to the electric vector ( E ) of the LP light. Cooperative reversion of the orientation direction for both the 4MAz and 4MCB groups was observed, and the orientational order, S, varied from ?0.79 to +0.75, without the side groups aggregating. The degree of the photoreaction and the distribution of the photoproducts from the 4MAz and 4MCB side groups through the axis‐selective photoreaction explain the reversion of the orientation direction. Optical recording, erasing, and birefringent control of the resultant oriented films were demonstrated by employing the photoisomerization of the 4MAz side groups using nonpolarised (NP) 405 nm light.

Order parameters of a P1 film after irradiating with LP 365 nm light (circles) and that following subsequent annealing (squares), as a function of exposure energy.     

Polymer‐Dispersed Liquid Crystals Based on Polystyrene and EBBA: Analysis of Phase Diagrams and Morphologies Generated

As an example of thermoplastic/liquid crystal blends that do not exhibit a liquid‐liquid immiscibility region in their phase diagrams, a polystyrene (PS)/N‐4‐ethoxybenzylidene‐4′‐butylaniline (EBBA) blend was analyzed. The complete phase diagram was built up using thermal transitions determined by differential scanning calorimetry (DSC) and polarized optical microscopy (POM). The boundary of the nematic + isotropic region was fitted with the Flory‐Huggins‐Maier‐Saupe model, extended to consider the polydispersity of PS. Main factors controlling the morphologies generated by thermal‐induced phase separation (TIPS) were the initial EBBA concentration in the blend and the cooling rate. Cooling at a fast rate led to small nematic domains with a narrow size distribution. Slow cooling rates led to the coexistence of very large and small dispersed domains. This was because of the large extent of coalescence of the droplets first generated associated with the continuation of the nucleation/growth process in a medium of increasing viscosity. The use of fast cooling rates might be important for the generation of a narrow size‐distribution of nematic droplets by TIPS in polymer‐dispersed liquid crystals (PDLC) used in electrooptical devices.

Micrograph obtained by transmission optical microscopy without crossed polarizers, showing nematic domains dispersed in a glassy matrix arising by a fast cooling of the blend from 130 °C; composition of blend: 70 wt.‐% EBBA.     

Optical,Electrochemical, Magnetic,and Conductive Properties of New Poly(indolocarbazole‐alt‐bithiophene)s

Summary: New alternating copolymers based on indolocarbazole (IC), both two‐ and three‐coupled, and bithiophene (BT) or bis(3,4‐ethylenedioxythiophene) (BiEDOT), were obtained using Stille or Suzuki coupling reactions. Those copolymers have been investigated by cyclic voltammetry, electrochemical quartz crystal microbalance, in situ electron spin resonance, in situ conductivity, and UV‐Vis‐NIR spectroelectrochemistry techniques. All polymer films undergo reversible oxidation processes. One to three isoelectronic oxidation processes, involving one electron per repeat unit, produce radical cations, dications, and radical trications. The oxidative charge is localized in the IC moiety for BT copolymers or over the whole polyconjugated backbone for BiEDOT copolymers. Redox neutral‐polaron conductivities are in the range of 0.02–0.1 S · cm^?1 and polaron‐bipolaron conductivities in the range of 0.1–0.7 S · cm^?1.

Chemical structure of the PIC derivatives.