Synthesis and Study of CdS Nanoparticle‐Doped Poly(1,4‐dihexyloxybenzene)

A simple, economical and high yielding method to prepare poly(1,4‐dihexyloxybenzene), an alkylated derivative of poly(para‐phenylene) (PPP), is reported. We further prepared a composite of poly(1,4‐dihexyloxybenzene) and CdS nanoparticles and studied their structural, optical, stability and transport properties. It was observed that the conductivity of poly(1,4‐dihexyloxybenzene) increased by several orders of magnitude when doped with CdS nanoparticles. Similarly, CdS nanoparticle‐doped PPP showed higher thermal stability, when compared to the neat polymer. As these composites could be processed in the same way as organic polymers, they would find applications in many low‐cost optoelectronic devices.

     

Use of PP Grafted with Itaconic Acid as a New Compatibilizer for PP/Clay Nanocomposites

Summary: Functionalized PP samples with different percentages of grafted IA, i.e., 0.7, 1 or 1.8 wt.‐%, with similar molecular weights were used as compatibilizers in PP/clay nanocomposites. PP nanocomposites containing 1 wt.‐% of organically modified clays, i.e., montmorillonite, natural hectorite and synthetic hectorite and 3 wt.‐% of grafted PP with three different percentages of grafted IA as compatibilizers and two commercial PP samples of different molecular weights were prepared by melt blending. The nanocomposites were characterized by XRD, TEM and tensile mechanical measurements. It was found that the molecular weight of PP used as matrix as well as the percentage of grafted IA of the compatibilizer affected the degree of intercalation/exfoliation of the clay and consequently the mechanical properties of the nanocomposites. Values of 2 137 MPa for the modulus and 51 MPa for the tensile strength were obtained when natural hectorite was used and 2 117 and 40 MPa were obtained when montmorillonite was used. A comparative study was carried out, where PP grafted with maleic anhydride was used as the compatibilizer. Inferior mechanical properties were obtained for nanocomposites prepared by using this compatibilizer, where values of 1 607 MPa for the tensile modulus and 43 MPa for tensile strength were obtained. This result indicated that IA‐grafted PP was far more efficient as compatibilizer for the formation of nanocomposites than commercially available maleic anhydride‐grafted PP.

Model showing interaction of the organically modified clay with grafted PP used as compatibilizer.     

Aromatic Polyethers with a 4‐Chloro‐3‐trifluoromethylphenyl Group

Summary: A novel bisphenol, (4‐chloro‐3‐trifluoromethyl)phenylhydroquinone (3FC‐PH), was synthesized via a three‐step synthetic procedure. Four aromatic polyethers based on 3FC‐PH were prepared via a nucleophilic aromatic substitution polycondensation. These polymers had a high thermal stability, and the temperatures at a 5% weight loss were above 516 °C in air. The solubility of the polyethers was improved by the introduction of bulky pendant groups. The average refractive indices of the polymer films at 1 320 nm were in the range 1.5381–1.6145. The dielectric constants of the polyether films estimated from the refractive indices were 2.69–2.98. Highly fluorinated 3FC‐PAE exhibited lower light absorption in the near‐IR region.

Part of the ¹H NMR spectra of 3FC‐PAE.     

An Efficient In Situ Polymerization Method for the Production of Polyethylene/Clay Nanocomposites: Effect of Polymerization Conditions on Particle Morphology

The effect of polymerization temperature, TIBA concentration, and zirconium loading on clay on the in situ polymerization of ethylene with clay‐supported metallocenes is investigated. Polymerization activity, clay exfoliation, and powder morphology are the response parameters. Zirconium loading on clay plays a determining role on polymerization activity and polymer/clay particle morphology, and increasing the polymerization temperature is found to facilitate clay exfoliation. A simpler procedure for in situ polymerization is also described in which the organoclay treated with trimethylaluminum acts as a cocatalyst in the presence of TIBA to obtain polyethylene/clay nanocomposites with acceptable activities and morphologies.

     

Synthesis of a Polyphenol with a Mesoionic 6‐Oxo‐1,6‐dihydropyrimidin‐3‐ium‐4‐olate as Pendant Group and Its Photochemical Behavior

This study deals with the synthesis of a polyphenol bearing photosensitive groups, and its photochemical behavior upon UV irradiation. Mesoionic 5‐(4‐hydroxybenzyl)‐6‐oxo‐1,2,3‐triphenyl‐1,6‐dihydropyrimidin‐3‐ium‐4‐olate was prepared by condensation of 4‐benzyloxybenzylmalonic acid with N,N′‐diphenylbenzamidine using dicyclohexylcarbodiimide as condensing agent, followed by deprotection of the benzyl group. The monomer was polymerized by an iron‐salen complex to give a polymer with a mesoionic 6‐oxo‐1,6‐dihydropyrimidin‐3‐ium‐4‐olate moiety as the pendant group. Spin coated polymer films were prepared and characterized. It was shown by IR spectroscopy that irradiation with UV light converted the mesoionic structure to a bis(β‐lactam) structure. Waveguide spectroscopy showed a large decrease in the film thickness without refractive index changes during irradiation.

Time development of the refractive index and the film thickness measured with p‐polarized light.     

Poly(4‐hexyl‐1,2,4‐triazole‐4H): An Electron Semiconducting Analogue to Regioregular Poly(hexylthiophene)

Summary: For the development of n‐channel field‐effect transistors it is indispensable to look for semiconducting polymers with electrons as majority charge carriers (n‐type). In addition high electron mobility values are of significant advantage in these compounds. Polymers with electron transporting properties have been rarely investigated. Main chain polymers with strong acceptor units like 1,2,4‐triazoles‐4H are potential candidates for electron transporting materials in electronic devices. Therefore, a synthetic pathway leading to an organo‐soluble polymer consisting only of 4‐hexyl‐1,2,4‐triazole‐4H units in the main chain is presented in this work. We will report the synthesis using modified classical polycondensation. The chemical and electronic properties of the polytriazole have been investigated in detail. The material has been used to prepare “electron‐only” devices for the calculation of the electron mobility.

The suggested chemical structure of poly(4‐hexyl‐1,2,4‐triazole‐4H) (PHTA).     

Multilayer Films Fabricated from Oppositely Charged Polyphenylene Dendrimers by Electrostatic Layer‐by‐Layer Assembly

Summary: Assemblies of oppositely charged L ‐lysine/carboxylic acid functionalized polyphenylene dendrimers and hybrid multilayers of L ‐lysine dendrimers/colloidal gold nanocrystals were fabricated as alternate multilayers on 3‐mercaptopropionic acid coated gold surfaces via layer‐by‐layer deposition. The fabrication of the multilayer films was monitored by kinetic and scan mode surface plasmon resonance spectroscopy. The permeability properties of the dendritic polyelectrolyte layers were characterized by electrochemistry in the presence of [Fe(CN)₆]^3?/4? as the redox couple. A high interfacial charge‐transfer resistance, originating from the electrostatic repulsion of the negatively charged redox couple against the negatively charged interface was observed and the charge‐transfer resistance found to increase with increasing number of layers.

3D‐structure of the investigated polyphenylene dendrimers: a) G₂(L ‐lysine)₈ and b) G₂(COOH)₁₆.     

Silicon‐Containing Cycloaliphatic Epoxy Resins with Systematically Varied Functionalities: Synthesis and Structure/Property Relationships

The manipulation of the properties of cycloaliphatic epoxy resins by systematical variations of the molecular structure is demonstrated. Specifically, four cycloaliphatic epoxy resins with silicon‐center linked via methyl, phenyl, and epoxy groups of different number were synthesized. The cured epoxides had remarkably changed crosslinking density from 0.45 × 10^?3 to 9.64 × 10^?3 mol · cm^?3, glass transition temperature from 133 to 237 °C, and considerably decreased thermal expansion coefficient from 6.44 × 10^?5 to 4.83 × 10^?5 K^?1. It was proved that the higher crosslinking density was related to more opened segments by wide‐angle X‐ray diffraction. The physical properties of cured products and their correlations with the chemical structures were investigated in detail.

     

Non‐Isothermal Crystallization of Poly(trimethylene terephthalate) (PTT)/Clay Nanocomposites

Summary: The non‐isothermal crystallization of intercalated poly(trimethylene terephthalate) (PTT)/clay nanocomposites was investigated quantitatively by different methods. Non‐isothermal crystallization of pure PTT can be described by the Ozawa equation, but the Ozawa theory is not valid for PTT/clay nanocomposites. The addition of clay into PTT decreases the crystallization half‐time while increasing the crystallinity and crystallization rate. The PTT/modified clay nanocomposites, in turn, have a higher crystallization rate parameter, k^1/n, and a lower crystallization half‐time compared to unmodified clay/PTT composites. The crystallization activation energy, calculated from Kissinger equation, of PTT, PTT/unmodified clay, and PTT/modified clay composites are 100, 180, and 198–230 kJ · mol^?1, respectively. Similarly, the nucleating activities of the unmodified clay and modified clays are 0.73 and 0.51–0.58, respectively. Although the addition of clay increases the crystallization activation energy, the clay still acts as an effective nucleating agent and increases the crystallization rate and crystallinity of PTT. Further, the modified nanoscale clays are more effective nucleating agents than the unmodified counterparts, and the most effective nucleating concentration of nano‐clay is between 1.0–3.0 wt.‐%.

The crystallization half‐time, t_1/2, decreases as a function of cooling rate, Q, and decreases with an increase in clay concentration.     

Site Specific Proton and Deuteron NMR Relaxation Dispersion in Selectively Deuterated Polyisoprene Melts

Summary: The frequency dependence of proton and deuteron NMR relaxation times was determined in selectively deuterated and undeuterated polyisoprene melts and compared to polybutadiene melts. Master curves were generated by the Williams‐Landel‐Ferry (WLF) formalism which resulted in very similar dispersions for all samples with a high and a low frequency branch following characteristic power laws. The results show a consistently weaker frequency dependence than any reported so far for other polymer melts. The reason for this finding is identified in the distribution of intramolecular motion modes, while intermolecular contributions are ruled out.

Master curves for ¹H relaxation dispersions obtained from measurements between 223 K and 348 K shifted relative to a reference temperature of 296 K.     

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.     

Palladium‐Catalyzed Phosphonation of Polyphenylsulfone

An efficient synthetic procedure for the phosphonation of aromatic polymers was developed and is here exemplified for polyphenylsulfone. This procedure involved the bromination of the polymer and the subsequent bromine‐phosphorus exchange by means of a Pd(0)‐catalyzed P? C coupling reaction. In the resulting product, the phosphonate ester pendant groups were attached to aromatic rings of the polymer chain without alkylene spacer units. A substitution degree of almost one phosphonate moiety per repeating unit of the polymer was achieved in the presence of Pd₂(dba)₃ · CHCl₃ as catalyst at 120 °C. Polymers with free phosphonic acid groups were prepared by ester hydrolysis.

     

Synthesis and Photovoltaic Properties of Side‐Chain Liquid‐Crystal Click Polymers for Dye‐Sensitized Solar‐Cells Application

SCLCPs are synthesized using “click chemistry”. The resulting polymers, P1 and P2, have good solubilities and molecular‐weight distributions. Their and polydispersities are in the ranges of 26.7–8.4 × 10³ g · mol^?1 and 1.99–1.29, respectively. DSC and POM studies reveal that both polymers exhibit liquid‐crystalline behavior. P1 and P2 are found to display blue emission. DSSCs are fabricated using P1 and P2 as matrices for electrolytes. The maximum PCE of the P1‐ and P2‐based polymer electrolytes is 4.11% (at 1 sun). This synthesis route has again proven to be a useful synthetic methodology for fabricating SCLCPs that are promising materials for device applications.

     

Viscoelastic Properties of Clay‐Containing Nanocomposites of Thermotropic Liquid‐Crystal Polymer

The nanocomposites of liquid‐crystal polymer (LCP) with two different weight per cents of clay were prepared via the melt extrusion method. To investigate the properties of the materials in the linear and non‐linear viscoelastic regions, both oscillatory and rotational tests were carried out. The results showed that the nanocomposite with higher clay content exhibited an almost defectless partially cross‐linked structure compared to the nanocomposite with lower clay content or the pure LCP. The linear stress relaxation measurements revealed that the pure LCP relaxed faster than nanocomposites after imposition of a constant strain for a specific time. During the step rate relaxation test, high shear rate modified the defects in the pure LCP very quickly and probably attained almost an equilibrium position while the nanocomposite samples showed strong shear thinning behaviour.

     

Enthalpy Relaxation of Layered Silicate‐Epoxy Nanocomposites

Using standard and temperature‐modulated differential scanning calorimetry, we have studied the segmental relaxation behavior of montmorillonite‐epoxy nanocomposites. The experimental results showed that the incorporation of clay particles caused the epoxy network to exhibit slower relaxation dynamics compared with the neat epoxy resin. Analysis based on the Tool‐Narayanaswamy‐Moynihan (TNM) model indicated that the nanocomposite systems had greater nonlinearity, higher apparent activation energy, and broader relaxation time distribution than the neat epoxy resin. Further analysis based on the Adam‐Gibbs model indicated that the presence of clay nanoparticles decreased the macroscopic configurational entropy of the epoxy network, and increased the size of the cooperative rearrangement region as well as the fundamental energy barrier. The peculiar relaxation behavior observed in the present experiments was attributed to the confinement effect of nanoparticles on molecular entities during the segmental relaxation. This confinement effect led to a stronger temperature dependence of the relaxation behavior near the glass transition temperature, or greater fragility. An inverse correlation between nonexponentiality and fragility was also observed, which is consistent with the results reported in the literature.

The original MDSC curves: complex heat capacity (C_{\rm P}^* ) versus temperature; the inset shows the nonexponentiality parameters (β) for all the samples.     

Nanocomposites of Hairy‐Rod Macromolecules: Concepts,Constructs, and Materials

The rational construction of nanocomposites based on so‐called hairy‐rod macromolecules (HRM) is the objective of this review covering 15 years of extensive research at the Max Planck Institute for Polymer Research. HRM are described as shape‐persistent objects, which are processed into ultrathin films by the Langmuir–Blodgett protocol. Transfer of monolayers initially formed on the water surface to solid substrates is understood as a two‐dimensional analogue of an extrusion process giving rise to molecular orientation phenomena. The scope of HRM concerning chemical composition and molecular architecture is reviewed, and examples of how to obtain complex constructs having device functions are given. Recent work on hairy‐rod polyelectrolytes based on poly(p‐phenylene sulfonates)s is summarized as well, and their ability to form hierarchical superstructures in aqueous solution is presented.

Assembly process of multilayers of hairy‐rod macromolecules by the LB technique.     

EPR Imaging Determination of High Molecular Weight Nitroxide Radicals in the UV Degradation of Polycarbonate‐Poly(acrylonitrile‐butadiene‐styrene) Polymers

The determination of nitroxide concentrations and distributions across plaques of polycarbonate/acrylonitrile‐butadiene‐styrene copolymer blend (PC/ABS) containing a high molecular weight hindered amine stabilizer (HALS) exposed to thermal and photochemical degradation treatments by EPR and EPR imaging (EPRI) is reported. Three different polymer compositions were examined: PC/ABS blends not‐pigmented and white pre‐pigmented with titanium dioxide; neat polycarbonate (PC); neat acrylonitrile‐butadiene‐styrene copolymer (ABS). The distribution profiles of the nitroxide radical in the various samples show large differences in the radical concentration across the plaques, these differences depending on the nature of the polymer and on the degradation treatment (thermal or photochemical). The experimental information provides important details on the mechanism of degradation of a complex polymeric matrix such as PC/ABS.

     

Control of the radical polymerization by 2,2,15,15‐tetramethyl‐1‐aza‐4,7,10,13‐tetraoxacyclopentadecan‐1‐oxyl and its sodium salt

The control of the radical polymerization of styrene by 2,2,15,15‐tetramethyl‐1‐aza‐4,7,10,13‐tetraoxacyclopentadecan‐1‐oxyl is reported here in bulk at 90 °C, 120 °C and in miniemulsion. Similarly, the control by its sodium complex is reported in bulk at 90 °C.

M _n vs. conversion for 3 , 3Na , and TEMPO.     

Novel Aromatic Polymer Electrolyte with Comb‐like Structure: Synthesis and Properties

Summary: A novel aromatic polymer electrolyte with pendant sulfodecyloxy groups was synthesized. The monomer 4 , bis[2‐(10′‐sulfodecyloxy)‐5‐chlorophenyl]sulfone, was synthesized from bis(2‐hydroxy‐5‐chlorophenyl)sulfide via bromoalkylation, oxidation, and sulfonation, and then polymerized via Ni‐catalyzed C C coupling polymerization to afford the title polymer electrolyte 6 . The polymer 6 was isolated as a brown powder with molecular weight of = 12 000. The high decomposition temperature of 6 (200 °C) was confirmed by TG/DTA‐MS measurement. Proton conductivity of 6 was measured using porous polyimide membrane as a supporting substrate. The pore‐filled membrane showed 1 × 10⁻⁵ S · cm⁻¹ of the proton conductivity at 80 °C and 90% RH.

Synthesis of aromatic polymer electrolyte having sulfodecyloxy groups via nickel‐catalyzed C C coupling polymerization.     

Synthesis and Characterization of α,ω‐Telechelic Polymers by Atom Transfer Radical Polymerization and Coupling Processes

Initiators for atom transfer radical polymerization (ATRP) bearing different functional groups (aldehyde, aromatic hydroxyl, dimethyl amino) were synthesized and characterized. Monotelechelics with low molecular weight were obtained by ATRP of styrene using these initiators in the presence of the CuBr/bpy catalytic complex. α,ω‐Telechelic polymers with double molecular weights with respect to the starting materials were prepared by coupling of monotelechelics under atom transfer radical generation conditions, in the absence of monomer, using CuBr as catalyst, tris[2‐(dimethylamino)ethyl]amine (Me₆TREN) as a ligand, under Cu⁰ mediated reductive conditions and with toluene as solvent. Terminal Br atoms present in monotelechelic polystyrenes (PS) as a consequence of the ATRP mechanism also offer other routes for preparing telechelic polymers. Aldehyde functionalized polymer was etherified with hydroquinone furnishing telechelic PS with a molecular weight that was two times higher. All polymers were characterized by spectral methods (NMR, IR spectroscopy) as well as by GPC.

Synthesis of initiators for atom transfer radical polymerization bearing different functional groups, for example, aldehyde, aromatic hydroxyl, dimethyl amino.