Spectroelectrochemical and Photovoltaic Characterization of a Solution‐Processable n‐and‐p Type Dopable Pyrrole‐Bearing Conjugated Polymer

D‐A‐D‐type polymers are of high interest in the field of photovoltaics and electrochromism. In this study we report the synthesis and electrochemical properties of PPyBT along with its photophysical properties and photovoltaic performance. PPyBT is soluble in common organic solvents and both n‐ and p‐type dopable, which is a desired property for conjugated polymers. During electrochemistry studies, the onset potentials of the polymer were determined as +0.2 V for oxidation and ?1.4 V for reduction. Using these values, HOMO and LUMO energy levels were calculated. The photovoltaic properties of PPyBT were also studied. PL studies showed that there is a charge transfer between PPyBT (donor) and PCBM (acceptor).

     

Side‐chain Cholesteric Liquid Crystalline Elastomers Derived from Nematic Bis‐olefinic Crosslinking Units

The synthesis of the nematic crosslinking agent (4′‐allyloxy‐benzoyl)‐(4″‐undec‐10‐en‐1‐oyl‐benzoyl)‐p‐benzenediolate ( M ‐ 1 ), the cholesteric monomer cholesteryl undec‐10‐en‐1‐oate ( M ‐ 2 ) and side‐chain cholesteric liquid crystalline elastomers is described. The chemical structures of the obtained monomers and elastomers were confirmed by FTIR and ¹H NMR spectroscopy. Their mesomorphic properties and phase behavior were investigated by differential scanning calorimetry, polarizing optical microscopy, and X‐ray diffraction measurements. The influence of the crosslinking M ‐ 1 units on phase behavior of different elastomers prepared by a one‐step hydrosilation reaction was discussed. The elastomers containing less than 20 mol‐% of the crosslinking M ‐ 1 units showed elasticity, reversible phase transition and cholesteric texture. The experimental results demonstrated that the glass transition temperatures and isotropization temperatures of P ‐ 2 ～ P ‐ 6 increased with increasing the concentration of crosslinking M ‐ 1 units.

Synthesis and schematic representation of elastomers.     

Effect of Molecular Structure and Thermal Treatment on Photo‐optical Properties of Photochromic Azobenzene‐containing Polymer Films

Three novel photochromic azobenzene‐containing comb‐shaped polyacrylates are synthesized and their phase behavior and photo‐optical properties are studied. The influence of the side photochromic group structure, thermal treatment, and light irradiation on aggregation of azobenzene chromophores in thin spin‐coated films of the polymers is investigated in detail. Special attention is paid to studying the photo‐orientation processes in polymers films induced by polarized blue light (473 nm). The relationship between the photochromic group architecture, phase behavior, thermal treatment of films, and kinetics of chromophore photo‐orientation is established and discussed. It is found that the position of the N?N bond in chromophores plays an important role in the kinetics of the process, but does not affect the maximum value of dichroism.

     

Preparation and Characterization of Acetoacetoxyethyl Methacrylate‐Based Gels

Novel polymeric gels have been prepared by radical copolymerization of acetoacetoxyethyl methacrylate (AAEM) and hydroxyethyl methacrylate (HEMA) in water‐ethanol medium. The influence of the HEMA:AAEM ratio and crosslinker concentration on properties of gels was studied. Independently on gel composition the maximum swelling was detected in chloroform. It was found that PAAEM gels possess phase transition temperature or upper critical solution temperature (UCST) in alcohol‐water solutions. UCST decreases in linear order from 75 to 10 °C when HEMA content in gel structure increases. The minimal UCST of AAEM/HEMA gels in binary alcohol‐water mixtures is shifted toward lower temperatures and lower alcohol concentrations when the alkyl chain of alcohol increases.

AAEM/HEMA gels prepared at different BIS concentrations (1:1 mol‐%, 2:2.5 mol‐%, 3:5 mol‐%).     

Photodeformable Polymers: A New Kind of Promising Smart Material for Micro‐ and Nano‐Applications

Summary: Starting in the 1960s, several kinds of photodeformable polymers have been developed, such as monolayers, polymer gels, solid films and liquid‐crystalline elastomers with different photodeformation mechanisms. This field evolved slowly until recently when significant achievements have been made. Most recently, Lendlein and co‐workers have put forward another new concept – using photo‐crosslinking to prepare deformable polymers with various pre‐determined shapes (Nature 2005 , 434, 879). This highlight gives a general introduction into photodeformable polymers and brings forth future challenges.

A polymer film doped with SCAA molecules where (a) is the permanent shape, (b) is the temporary shape and (c) is the recovered shape.     

Oxidative Coupling Copolymerization of 4‐Methyltriphenylamine with Arenes

A novel synthetic method for the preparation of high‐molecular‐weight conjugated polymers is presented. It consists of the oxidation copolymerization of different arenes with triphenylamine. The structure of the copolymers was characterized by ¹H and ¹³C NMR spectra. The copolymers have good solubility in common organic solvents and are thermally stable. Photoluminescence (PL) spectra (see Figure) showed that the color of emission depends on the type of arene units in the copolymer chain. Cyclic voltammetry (CV) measurements revealed electrochemical activity of the copolymers.

PL spectra of the copolymers.     

Functionalisation of Polyolefins: Grafting of Phenol Groups on Olefin/5,7‐Dimethylocta‐1,6‐diene Copolymers

The grafting of phenol groups on ethylene/5,7‐dimethylocta‐1,6‐diene copolymers and on ethylene/propylene/5,7‐dimethylocta‐1,6‐diene terpolymers was performed, using two different modification procedures. An indirect route involving hydrochlorination followed by phenol insertion was found to be very effective for the terpolymers, and lead to a grafting phenol rate higher than 75%. However, if the phenol grafting is performed directly on a non‐modified terpolymer, lower rates are obtained. When applied to the copolymers the procedures used were revealed to be less efficient. This fact might be related to the lower solubility of the ethylene/5,7‐dimethylocta‐1,6‐diene copolymers (related to a higher crystallinity and a smaller diene content) when compared with the corresponding terpolymers. Although incomplete, the addition of a hindered phenol to the copolymer gave rise to a polymer that, when compared to polyethylene, presents a higher thermal‐oxidative stability.

Grafting of phenol on a hydrochlorinated ethylene/propylene/5,7‐DMO terpolymer.     

Phase Behaviour of New Side‐Chain Liquid Crystalline Polyoxetanes

Summary: The synthesis and thermal behaviour of two new polyoxetanes with side chains having a dimer structure mesogen‐spacer‐mesogen and a long terminal alkyl group are reported. The two polymers differ in the chemical structure of the central spacer. The polyoxetanes have been obtained by cationic ring‐opening polymerisation of an appropriately substituted oxetane ring. Both polyoxetanes studied exhibit liquid crystalline properties showing a similar sequence of phases. DSC and synchrotron experiments indicate that a highly ordered phase with a probable orthorhombic packing is observed at low temperature. On heating, this phase melts into a mesophase with hexagonal order within the smectic layers, which, on further heating, is transformed into a disordered smectic mesophase.

Synchrotron X‐ray diffraction patterns of one of the poyoxetanes in a heating experiment.     

Synthesis of Norbornene Derivatives by Diels‐Alder Cycloaddition and Subsequent Copolymerization with Maleic Anhydride

Summary: Several norbornene (Nb) derivatives were synthesized by facile Diels‐Alder cycloaddition reactions of cyclopentadiene with α‐olefins containing electron‐withdrawing groups such as nitrile (CN), phosphonate, and ester. The Diels‐Alder adducts were subsequently copolymerized with maleic anhydride (MAH) using free radical polymerization conditions previously determined for MAH/Nb copolymerizations. Further functionality was introduced into the copolymers through acid‐catalyzed hydrolysis of poly(Nb‐alt‐MAH) and poly(NbCN‐alt‐MAH) copolymers. FTIR confirmed hydrolysis of the anhydrides to carboxylic acid‐functionalities and indicated no appreciable hydrolysis of the nitrile functionality. Observed copolymerization rates (k_obs) were measured using in situ FTIR. A dramatic decrease in the rate of copolymerization was observed for the Nb derivatives that contained a strong electron‐withdrawing functionality. This observation suggested a significant electronic influence on the free radical copolymerization rate with maleic anhydride due to the electron‐withdrawing nature of the Nb substituents.

Vinylene region of in situ FTIR “waterfall” plot for 50/50 Nb/MAH alternating copolymerization.     

Synthesis of Laser‐Alignable Liquid Crystalline Conducting Polymers

Summary: The synthetic routes to three series of liquid crystal conducting polymers (based on pyrrole, thiophene, and aniline monomers) are reported and the optimum conditions for polymer preparation are described. These polymers show increased conductivity when laser‐aligned, the greatest effect being shown by the N‐substituted pyrrole‐based system. Information on their liquid crystal and spectroscopic properties and other characteristics are also included.

Structure of the monomers M1, M2, and M3.     

Preparation and Properties of Cholesteric Network Polymers Based on Liquid Crystalline Epoxides

Summary: Polyether network polymers with cholesteric superstructure are formed by the photochemically induced cationic copolymerisation of a nematic diepoxide with chiral epoxides. If a cholesteric superstructure is formed or not, depends on the temperature at which the photopolymerisation is carried out. The storage modulus is higher above T_G in samples with cholesteric superstructure. Optical rotations and vibrational circular dichroism spectra (VCD) depend strongly on the surface state of the substrates. From the VCD spectra it is concluded that the copolymerisation leads to different superstructures depending on the rub directions of the substrates.

IR absorption spectrum and VCD spectrum of the cholesterol derivative 4 .     

Facile Synthesis of Nanoporous Hydroquinone/Catechol Formaldehyde Resins and their Highly Selective,Efficient and Regenerate Reactive Adsorption for Gold Ions

We present a new type of nanoporous hydroquinone/catechol formaldehyde resin synthesized by a one‐pot route, with a surface area of up to 1 112 m² · g^?1. The resins show highly efficient reactive adsorption for silver/gold (silver adsorbance up to 2.43 g · g^?1) and excellent selectivity for gold (K_d is as high as 1 914 090 mL · g^?1). The first‐used resins can be regenerated with NaHSO₃, and the gold capacities of the recycled PCFR and PHFR reach 44 and 78% of their first loading capacities, respectively.

     

Reconstruction of Achiral Polymer for Structural Chirality Using Cholesteric Liquid Crystal Medium and Light‐Driven Chiroptic Modulation

A series of optically inactive polythiophene derivatives bearing the azobenzene moiety are synthesized in an isotropic toluene solution. The polymers are then dissolved in a cholesteric liquid crystal (Ch*LC) medium within the liquid crystal (LC) temperature range. The dissolution process in Ch*LC produces intermolecular π‐stacking with structural chirality. Although the polymers thus prepared have no chiral center or axial chirality in the primary structure, they do exhibit consistent chiroptical activity derived from three‐dimensional chiral aggregations. Furthermore, photochemical cis–trans isomerization of the substituents allows light‐driven chiroptic modulation of the polymer.

     

Chemical Binding of Unsaturated Fluorenes to Poly(2‐chloroxylylene) Thin Films

A series of substituted fluorenes with vinyl groups as reactive sites were synthesized and characterized. Fluorene‐based polymers with vinyl groups as end chains and side chains functionalities were also prepared. In both cases, successful preparation of functionalized Parylene C films (modylayers) was achieved. The set of spectral methods used has allowed us to conclude that such functionalization is based on the chemical reaction of double bonds with xylylene radicals during deposition process. Parylene C films chemically modified with specially synthesized polyfluorenes showed PL quantum efficiency comparable with neat polyfluorenes.

     

Nanoscale Blends between Immiscible Polymers via Simultaneous Non‐Interfering Polymerisation

Summary: An important topic in polymer science seeks to improve the performances of polymer blends using nanoscale phase segregation. Here, blends between polystyrene and polycaprolactone are realised by a chemical route. The non‐interfering character of the radical polymerisation of styrene and the lanthanide halide initiated ring‐opening polymerisation of caprolactone is assessed. The molecular weights range from 2 000 to 3 500 for polycaprolactone and up to 140 000 for polystyrene, with reasonable polydispersity indexes. From calorimetry measurements, it is shown that polystyrene and low molecular weight polycaprolactone are immiscible. The morphology of the blends between the two immiscible polymers studied by atomic force microscopy is consistent with nanometer‐scale phase segregation.

AFM surface image of a nanoscale blend.     

Structure and Properties of Poly(butyl acrylate‐block‐sulfone‐block‐butyl acrylate) Triblock Copolymers Prepared by ATRP

Summary: A series of telechelic OH polysulfones (PSU) were converted to atom transfer radical polymerization (ATRP) macroinitiators by reaction with 2‐bromoisobutyryl bromide. Three macroinitiators with different chain lengths were extended with poly(butyl acrylate) (PBA) to form ABA triblock copolymers. The structure and dynamics of the ABA triblock copolymers with PSU central segments and various molecular weight PBA side chains were investigated by small‐angle X‐ray scattering and rheology. The block copolymers form micelles with a PSU core and PBA corona. The length of each block has an important effect on the structure and resulting dynamics of the copolymers. Dynamic mechanical measurements indicate three relaxation modes: (i) PBA segmental relaxation at high frequency; (ii) PBA relaxation of the corona block at intermediate frequency; (iii) an additional relaxation process related to structural rearrangement of the micelles at low frequency. The shear modulus plateau corresponding to a soft rubbery state extends over a very broad time or temperature range because of this slow additional relaxation.

Schematic illustration of the structural elements and the bulk supramolecular structure for a symmetric triblock copolymer with a stiff central segment strongly incompatible with the other constituent.     

Pseudo‐Living Anionic Telomerization of Buta‐1,3‐diene

Low‐molecular‐weight liquid polybutadienes (1 000–2 000 g · mol^?1) consisting of 60 mol‐% poly(buta‐1,2‐diene) repeating units were synthesized via anionic telomerization. Maintaining the initiation and reaction temperature at less than 70 °C minimized chain transfer and enabled the polymerization to occur in a living fashion, which resulted in well‐controlled molecular weights and narrow polydispersity indices. MALDI‐TOF mass spectrometry confirmed that the end groups of liquid polybutadienes synthesized via anionic telomerization contained one benzyl end and one protonated end. In comparison, the end groups of liquid polybutadienes synthesized via living anionic polymerization contained one sec‐butyl or butyl end and one protonated end.

     

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.     

Novel Side‐Chain Polyrotaxane with Cyclodextrin: Syntheses and Study of Water‐Soluble Copolymers Bearing Hydrophobically Associative Components

Summary: Novel water‐soluble hydrophobically associative polymers, comprising sodium 2‐acrylamido‐2‐methylpropansulfonate , N,N‐dimethylacrylamide and different amounts of a hydrophobically associative macromonomer, were synthesized in an aqueous medium. Formation of a rotaxane‐like complex of this macromonomer, with randomly methylated β‐cyclodextrin, was studied. In addition, a side chain of polyrotaxane, comprising this complex and methyl methacrylate, was synthesized via ATRP. These polymers were characterized by dynamic light scattering and fluorescent‐probe technique. Effects of methylated β‐cyclodextrin on micelle formation of the polymers were also studied.

The side‐chain polyrotaxane.     

Metathetic Selective Degradation of Polyisoprene: Low‐Molecular‐Weight Telechelic Oligomer Obtained from Both Synthetic and Natural Rubber

Summary: Degradation studies of cis‐1,4‐polyisoprene were carried out using first and second generation Grubbs catalysts to achieve end‐functionalized acetoxy oligomers in both an organic solvent and a latex phase at room temperature. Well‐defined acetoxy telechelic polyisoprene structures were obtained in a selective manner with a range of from 10 000 to 30 000, with a polydispersity index of around 2.5.

Structure produced by the metathetic depolymerization of hydroxy telechelic cis‐1,4‐polyisoprene.