Polymer/layered silicate nanocomposites: a review from preparation to processing

This review aims at reporting on very recent developments in syntheses, properties and (future) applications of polymer-layered silicate nanocomposites. This new type of materials, based on smectite clays usually rendered hydrophobic through ionic exchange of the sodium interlayer cation with an onium cation, may be prepared via various synthetic routes comprising exfoliation adsorption, in situ intercalative polymerization and melt intercalation. The whole range of polymer matrices is covered, i.e. thermoplastics, thermosets and elastomers. Two types of structure may be obtained, namely intercalated nanocomposites where the polymer chains are sandwiched in between silicate layers and exfoliated nanocomposites where the separated, individual silicate layers are more or less uniformly dispersed in the polymer matrix. This new family of materials exhibits enhanced properties at very low filler level, usually inferior to 5 wt.%, such as increased Young’s modulus and storage modulus, increase in thermal stability and gas barrier properties and good flame retardancy.

Polymer-layered silicate nanocomposites: preparation, properties and uses of a new class of materials

A review was presented to demonstrate a historical description of the synthesis of light-emitting conjugated polymers for applications in electroluminescent devices. Electroluminescence (EL) was first reported in poly(para-phenylene vinylene) (PPV) in 1990 and researchers continued to make significant efforts to develop conjugated materials as the active units in light-emitting devices (LED) to be used in display applications. Conjugated oligomers were used as luminescent materials and as models for conjugated polymers in the review. Oligomers were used to demonstrate a structure and property relationship to determine a key polymer property or to demonstrate a technique that was to be applied to polymers. The review focused on demonstrating the way polymer structures were made and the way their properties were controlled by intelligent and rational and synthetic design.

Synthesis of Light-Emitting Conjugated Polymers for Applications in Electroluminescent Devices

A review on polymer–layered silicate nanocomposites

This article provides a review about electroluminescence from organic materials and deals in detail with organic light-emitting diodes (OLEDs), light-emitting electro-chemical cells (LECs) and electrogenerated chemilumi-nescence (ECL) reflecting different electrooptical appli-cations of conjugated materials. It is written from an organic chemist's point of view and pays particular attention to the development of organic materials involved in corresponding devices. In recent years a substantial amount of both academic and industrial research has been directed to organic electroluminescence in an effort to improve the processability and tunability of organic materials and the longevity of OLEDs and LECs. On the eve of the commercialization of organic electrolumi-nescence this review provides an overview of lifetimes and efficiencies attained and reflects materials and device concepts developed over the last decade. In this context electrogenerated chemiluminescence is discussed with respect to its importance as a versatile tool to simulate the fundamental electrochemical processes in OLEDs.

The electroluminescence of organic materials

Poly(methyl methacrylate)–polystyrene composite particle latexes were prepared by poly(methyl methacrylate)-seeded emulsion polymerization of styrene employing batch, swelling-batch, and semibatch methods. The changes in particle morphology taking place during the polymerization reaction were followed by electron microscopy. Anchoring effect exerted by ionic terminal groups introduced by ionic initiator was found to be the main factor in controlling the particle morphology. The polymer particles obtained by oil-soluble hydrophobic initiators such as azobisisobutyronitrile and 4,4′-azobis-(4-cyanovaleric acid) gave the inverted core-shell morphology. Water-soluble hydrophilic initiator, K2S2O8, also gave the inverted core-shell morphology. However, in this case the occurrence of the halfmoonlike, the sandwichlike, and the core-shell morphologies were also observed depending upon the polymerization conditions. The distribution of terminal SO groups on the surface area of polystyrene particles could be controlled by initiator concentration and polymerization temperature. Viscosity of polymerization loci dictated the movement of polymer molecules, thus causing the unevenness of particle shape and phase separation at high viscosity state. Viscosity was controlled by the styrene/poly(methyl methacrylate) ratio, the addition of a chain transfer agent or a solvent which is common to polystyrene and poly(methyl methacrylate).

Morphology of latex particles formed by poly(methyl methacrylate)-seeded emulsion polymerization of styrene

Styrene monomer was mixed with quaternary ammonium montmorillonites(org-MMTs) and polymerized in the presence of radical initiator. The resulting materials showed an expansion of interlayer distance. These hybrid materials exhibited higher thermal stability compared with the virgin polystyrene(PS) or PS/pristine-MMT microcomposite. PS/Bz-MMT, containing benzyl-unit similar to styrene in org-MMT, exhibited higher decomposition temperature even for MMT loading as low as 0.3wt.% compared with other PS/org-MMT hybrids. It was found that the structural affinity between styrene monomer and the organic group of org-MMT plays an important role in the structure and the properties of hybrid materials.

Synthesis and properties of polystyrene-organoammonium montmorillonite hybrid

Various derivatives (ethoxycarbonylmethyl, carboxymethyl, and ethoxyethyl, etc.) of calix[4]arene, calix[6]arene, and calix[8]arene have been synthesized and their ion-binding properties investigated by solvent extraction, ion-transport through liquid membranes, and u.v. spectroscopy. The extraction of various metal ions (as picrate salts) from the aqueous phase into dichloromethane by the calixarene derivatives showed that the ethoxycarbonylmethyl derivatives exhibited markedly increased extraction efficiency compared with their unsubstituted phenol analogues, and the efficiency was in general comparable to those of crown ethers. The most notable feature was the selectivities exhibited by their ethoxycarbonylmethyl derivatives; calix[4]arene for Na+, calix[6]arene for Cs+, and calix[8]arene for K+. A liquid membrane study with a water–chloroform–water system also indicated that the ion-transport efficiencies exhibited by calixarenes were found to be in accordance with their extraction abilities, confirming the strong participation of the ester carbonyl oxygen in this function. However, the ester derivative of calix[4]arene was an exception in that inefficient carrier activity was observed in spite of high extraction efficiency. The pronounced Cs+ selectivity exhibited by the calix[6]arene ester was further confirmed by the changes in the u.v. spectrum of the ester from 277 and 270 nm to 275 and 267 nm upon interaction with Cs+ ion in methanol.

New metal cation-selective ionophores derived from calixarenes: their syntheses and ion-binding properties

New discogens based on the octasubstituted phthalocyanines (Pc) were synthesized: 2,3,9,10,16,17,23,24-octakis[dodecylthio-1-methyl]-phthalocyanine (1a), 2,3,9,10,16,17,23,24-octakis[4-(dodecylthio)-2-oxa-butyl]-phthalocyanine (1b), 2,3,9,10,16,17,23,24-octakis[dodecyloxy]-phthalocyanine (1c), phthalocyanine 2,3,9,10,16,17,23,24-octa-n-dodecanoate (1d), S-(+)-2,3,9,10,16,17,23,24-octakis[4-(dodecyloxy)-2-oxa-pentyl]-phthalocyanine (1e), as well as their corresponding copper complexes (CuPc) 2a, 2b, 2c and 2e. They were characterized by microanalysis, IR, 1H and 13C NMR spectroscopies, and their mesomorphic behaviors were examined with DSC and optical microscopic methods. The products exhibited the following optical textures and transition temperature ranges: focal conic (1a, 95-267°; 2a, 108-304°), linear default (1b, 52-247°; 2b, 70-255°; 1c, 75-269°; 2c, 78-310°), fan-shaped (1d, 58-303°; 2e, 29-191°). Chiral discogenic PcH2 1e, however, showed a cholestericlike texture (23-151°C) in which the ...

Synthesis and Morphology of New Discogenic Phthalocyanine Derivatives

Glycolide (GL) and e-caprolactone (CL) were copolymerized in bulk at relatively high temperatures using stannous octoate as a catalyst. To investigate the relationship among microstructure, thermal properties, and crystallinity, three series of copolymers prepared at various reaction temperatures, times, and comonomer feed ratios were prepared and characterized by 1 H and 13 C NMR, DSC, and wide-angle X-ray diffraction (WAXD). The 600-MHz l H NMR spectra provided information about not only the copolymer compositions but also about the chain microstructure. The reactivity ratios (r G and r G ) were calculated from the monomer sequences and were 6.84 and 0.13, respectively. In terms of overall feed compositions, the sequence lengths of the glycolyl units calculated from the reactivity ratios exceeded those measured from the polymeric products. Mechanistic considerations based on reactivity ratios, monomer consumption data, and average sequence lengths are discussed. The unusual phase diagram of GL/CL copolymers implies that the copolymer melting temperature does not depend on its composition alone but rather on the nature of the sequence distribution. The DSC and WAXD measurements show a close relationship between polymer crystallinity and the nature of the polymer sequence.

Iwhan Cho

Papers

Morphology of latex particles formed by poly(methyl methacrylate)-seeded emulsion polymerization of styrene

Synthesis and properties of polystyrene-organoammonium montmorillonite hybrid

New metal cation-selective ionophores derived from calixarenes: their syntheses and ion-binding properties

Synthesis and Morphology of New Discogenic Phthalocyanine Derivatives

Microstructure analysis and thermal property of copolymers made of glycolide and ?-caprolactone by stannous octoate