Electroluminescent Conjugated Polymers—Seeing Polymers in a New Light

A new exciting interdisciplinary research field has evolved following the discovery that conjugated polymers can emit light when put into light-emitting diodes. A myriad of light-emitting polymers (examples of which are shown below) shining in various colors have been developed through chemical intuition and structural design.     

Oligophenyls,Oligophenylenes, and Polyphenyls,a Class of Thermally Very Stable Compounds

The classical and modern syntheses of oligophenyls and polyphenyls are compared to illustrate the value and the range of applications of the preparation methods described. The investigations showed a relationship between the number, arrangement, and substitution of the aromatic rings and the physical properties of the products. The melting point of the p-polyphenyls rises with increasing degree of condensation. Methylation, and linkage in the m-positions lowers the melting point and at the same time improves the solubility. o-Oligophenyls melt at lower temperatures than the p-isomers. The highest-melting substance in this class in p-septiphenyl, which melts at 545 °C.     

Perspectives in the Development of High-Temperature Polymers

Research on high-temperature organic polymers was initiated in the late 1950s primarily to meet the needs of the aerospace and electronics industry. Since then, many different heat-resistant polymer systems have been reported, of which several are now commercially available. These polymers are used in many diverse applications such as circuitry in microelectronic components, coatings on cookware, binders in brake systems, sealants for fuel tanks in high-speed aircraft, gears in copying machines, structural components in high-speed aircraft, and space vehicles, films and wire coatings for electrical insulation. Worldwide use for high-temperature polymers in 1988 was estimated at 90 million kilograms with a value of $ 2.3 billion. This market is expected to double by the end of this decade. The major polymer classes discussed in the present paper are polyimides and poly(aryl ethers).     

New Forms of Carbon

A number of novel carbon materials whose unique properties fit them for many uses have recently been developed. Pyrolytic graphites are excellent conductors of heat and electricity parallel to the surface, whereas they are semiconductors perpendicular to the surface. A similar anisotropy is found in graphite foils, which are impermeable, but also very flexible. Glasslike carbon, which is also impermeable, is, however, completely isotropic. Carbon foams and felts are extremely light and exhibit very good thermal insulation up to high temperatures. In addition to very high strength, carbon fibers have values of Young's modulus greater than that of any other fibers or wires. Carbon fiber/resin composites are therefore more rigid than any other known materials; their specific Young's modulus is five times that of steel.     

Advanced Materials: Trends and Possibilities in Liquid Crystalline Polymers

During the past ten years there has been a sharp increase in interest in the opportunities afforded by R & D in the field of specialty polymers. Interest is mainly being shown in two distinct categories of polymers, namely, (a) polymers which are used in very small quantities to fulfill critical needs as a part of device system, and (b) high-performance engineering polymers which significantly extend their mechanical and thermal properties for structural applications. The first category ranges from advanced resists and insulating layers for microelectronic devices to membranes for filtration systems. The second category encompasses improved matrices for advanced composites as well as liquid crystalline polymers. In the present paper an overview is first given of the emerging opportunities for advanced materials and particularly specialty polymers. The status of work on liquid crystalline copolyesters is then discussed with special emphasis on one of the major problems confronting this field, namely interpreting the microstructure of the copolyesters.     

Ultrasonic Studies of Solid Polymers

For over a quarter of a century the ultrasonic technique has provided scientists with a probe for investigating the energy transfer and storage characteristics of atomic and molecular systems. Most notable among these early studies were those concerned with establishing the form of the Fermi contact surface in metals [l], vibrational relaxation in molecular gases [2], and ion-solvation equilibria in aqueous solutions [3]. In more recent years the technique has been used to study the dynamics of conformational change in simple ethanes [4], alicyclic and heterocyclic molecules [5], and flexible polymers [6]. This review is concerned with a comparison of the factors influencing the propagation of an acoustic wave through synthetic polymers, glasses, and dielectric solids.     

NMR Microscopy and Image Processing for the Characterization of Flexible Polyurethane Foam

NMR tomography in material science? Three-dimensional images with a spacial resolution of 10 μm are now possible for porous, liquid-containing materials with NMR microscopy. They can be processed further with image evaluation methods and used, for example, for the characterization of open-cell foams (see illustration).     

Potentialities of a New Class of Anticlotting and Antihemorrhagic Polymers

Major blood anticlotting agents may be grouped into two classes: 1) heparin and heparin analogs, 2) coumarin and coumarin analogs.

The first class of compounds interferes with the formation of thrombin and thromboplastin whereas the second inhibits the formation of prothrombin. Both classes have their own antagonists; namely, protamine sulfate types and vitamin K types exhibiting antihemorrhagic properties.

On a molecular level the heparinlike structures and their antagonists may be regarded as polyanions and polycations, respectively, whereas the coumarinlike structures and their antagonists as electron donors and acceptors, respectively, which may form charge transfer complexes.     

Synthesis and Properties of a New Class of Potential Biomedical Polymers

Both low molecular weight compounds and some polyelectrolytes containing quaternary nitrogen atoms in their structure have been known for some time to possess important biological activity. Aliphatic ammonium compounds are used as bacteriocides and muscle relaxants, and quinolinium compounds have recently been found to be excellent antileukemic agents. In addition, a considerable amount of evidence has been accumulated to show that organic ammonium salts combine with heparin, and the resulting complex may be used as a coating to render polymers blood-compatible. However, the introduction of ammonium groups into the backbone of a polymer exhibiting good mechanical properties offers certain advantages.     

Routes to New Aromatic Polycarbonates with Special Material Properties

Polycarbonate together with the acrylonitrile/butadiene/styrene copolymers, and the poly amides constitute the leading groups of engineering thermoplastics; for polycarbonate in particular, continued dynamic growth is prophesized. The underlying reason for this lies not only in its outstanding combination of technical properties and excellent price/performance balance, but also in the chemical and physical potential inherent in the basic structure of polycarbonate. The following review demonstrates with examples how this potential can be used in the development of new polycarbonates through the incorporation of alternative monomers, changes in the linear structure, end group variation, addition of special additives, and blending. The main emphasis of this articles lies in the development of polycarbonates resistant to high temperature, with a good balance of technologically valuable properties. For scientific and practical interests a new criterion is offered for polycarbonates having both high-temperature stability and impact strength. “One must not only make a discovery, but also realize that a discovery has been made.” Hermann Schnell [1]     

New Routes to Multicomponent Oxide Glasses

Multicomponent oxide glasses can be produced not only by melting methods but also by hydrolysis and condensation of alkoxide complexes with several metals. This requires temperatures only up to the transformation range of the glass in question, usually 500–600 °C. The process does not pass through the molten phase. It is possible to obtain glasses or polycrystalline substances, depending on the composition. The method is particularly suitable for the production of thin, transparent multicomponent oxide layers of almost any composition on substrates. Some of these layers provide protection against climatic attack or against oxidation.     

Synthesis and Self‐assembly of a Helical Polymer Grafted from a Foldable Polyurethane Scaffold

Herein a polyurethane graft poly‐l ‐glutamate amphiphilic copolymer was synthesized from a polyurethane (PU)‐based macro‐initiator (containing pendant primary amine groups) through the ring opening polymerization of N‐carboxy anhydride of γ‐benzyl‐l ‐glutamate ( BLG‐NCA ). On average, twenty two l ‐glutamic acids were grafted from each amino group which was pendant on the polyurethane chain with 10 repeating units. The grafted polymer ( PU‐PP‐1 ) exhibits self‐assembly to produce a hydrogel in a wide pH window ranging from pH 5.0 to 8.0 with a critical gelation concentration (CGC) of 5.0 wt % (w/v) at pH 7.4. Furthermore, circular dichroism study revealed the transition of the α‐helix to a random coil upon increasing the pH. Due to the protonation of side chains at pH 4.0, PU‐PP‐1 adopted an α‐helical conformation whereas at pH >8.0 the side‐chain carboxylic acid groups of the PLGAs were ionized, leading to the formation of an extended random coil conformation as a result of charge repulsion. Conformational switching was also supported by FTIR spectroscopy.     

磺酸型聚氨酯离聚物的离子导电性能

本文以多种聚醚为软段，二异氰酸酯（ＭＤＩ和ＴＤＩ）为硬段，合成了多嵌段聚醚聚氨酯，以此聚氨酯为基材，与ＮａＨ及１，３－丙碳酸内酯反应，进一步合成了一系列不同离子化程度的阴离子型碳化聚氨酯离聚物，用交流阻抗谱仪测定了样品的阻抗谱，由此计算出样品的离子电导率。研究结果表明其他条件相同时，以聚乙二醇（ＰＥＧ）为软段的样品具有较高的离子电导率；以聚环氧丙烷（ＰＰＯ）为软段的样品次之，以聚四氢呋喃（ＰＴＭＯ）为软段的样品最低，对于离子化程度不同的聚氨酯离聚物以金属离子和烷氧单元之比为０．０５时导电性能最好。阳离子为Ｌｉ＋和Ｎａ＋的样品具有相近的离子电导率。     

Mixture of Azolium Tetraphenylborate with Isopropylthioxanthone: A New Class of N-Heterocyclic Carbene (NHC) Photogenerator for Polyurethane,Polyester, and ROMP Polymers Synthesis

In the search of smarter routes to control the conditions of N-heterocyclic carbene (NHCs) formation, a two-component air-stable NHC photogenerating system is reported. It relies on the irradiation at 365 nm of a mixture of 2-isopropylthioxanthone (ITX) with 1,3-bis(mesityl)imidazoli(ni)um tetraphenylborate. The photoinduced liberation of NHC is evidenced by reaction with a mesitoyl radical to form an NHC-radical adduct detectable by electron spin resonance spectroscopy. The NHC yield can be determined by ¹H NMR spectroscopy through the formation of a soluble and stable NHC–carbodiimide adduct. To deprotonate the azolium salt and liberate the NHC, a mechanism is proposed in which the role of base is played by ITX radical anion formed in situ by a primary photoinduced electron-transfer reaction between electronically excited ITX (oxidant) and BPh₄⁻ (reductant). An NHC yield as high as 70 % is achieved upon starting with a stoichiometric ratio of ITX and azolium salt. Three different photoNHC-mediated polymerizations are described: synthesis of polyurethane and polyester by organocatalyzed step-growth polymerization and ring-opening copolymerization, respectively, and generation of polynorbornene by ring-opening metathesis polymerization using an NHC-coordinated Ru catalyst formed in situ.     

Synthesis of Flexible Elastomeric Polyurethane Films with High Elasticity and Evaluation of Their Structural Permanency

Flexible elastomeric polyurethane (EPU) films were synthesized by ultraviolet (UV) curing of thermoplastic polyurethanes (TPUs) through the reaction among poly (oxytetramethylene) diol (PTMO), isophorone diisocyanate (IPDI), cis-2-butene-1,4-diol (cis-BDO), and 1,6-hexanediol diacrylate (HDDA). In order to improve elasticity and structural permanency in the synthesized TPUs, cross-linking reaction involving unsaturated groups of chain extender (cis-BDO) and reactive diluent (HDDA) using 27 and 41 seconds of UV radiation is introduced. Investigation of structure and mechanical properties was performed using FTIR, GPC, and tensile tests. Stress-strain behavior showed that Young's moduli of EPUs were in the range of 0.2 to 0.4 MPa, which is evidence for high flexibility. Three times of repeated loading on one sample up to 100% strain with 10 min intervals for its recovery showed that considerable structural change didn't occur under these conditions and all observed permanent sets vanished within a time not exceeding 10 min.     

Benzocyclobutenes: A New Class of High Performance Polymers

Benzocyclobutenes are a family of thermally polymerizable monomers which can be classified into two groups: 1) monomers which contain only benzocyclobutene moieties and 2) monomers which contain sites of unsaturation in addition to benzocyclobutene moieties. The monomers can be partially polymerized (B-staged) by heating to form oligomers having processing advantages for various composite fabrication techniques. The polymerization proceeds through the thermally initiated cyclobutene ring opening to yield an o-quinodimethane intermediate (calculated to be a ground state singlet). Preliminary characterization of the network structures indicates that monomers which contained multiple benzocyclobutene moieties, optionally with sites of unsaturation, were transformed into multifunctional network junctions when the thermosets were fully cured. The 3-maleimidobenzocyclobutenes thermally polymerize to yield substantially linear, high glass transition temperature (T_g) polymers. Thus benzocyclobutene polymers encompass materials which have properties ranging from high T_g, thermosets to those of substantially linear thermoplastics. Some polymers exhibit an excellent retention of their room temperature mechanical properties to at least 200-250°C, making them useful as high performance polymers for applications in the aerospace industry. Other polymers have outstanding electrical properties including very low dielectric constant and water pickup, making them useful in electronic applications.     

Oxidative and Photochemical Stability of Ionomers for Fuel‐Cell Membranes

To predict hydroxyl‐radical‐initiated degradation of new proton‐conducting polymer membranes based on sulfonated polyetherketones (PEK) and polysulfones (PSU), three nonfluorinated aromatics are chosen as model compounds for EPR experiments, aiming at the identification of products of HO^.‐radical reactions with these monomers. Photolysis of H₂O₂ was chosen as the source of HO^. radicals. To distinguish HO^.‐radical attack from direct photolysis of the monomers, experiments were carried out in the presence and absence of H₂O₂. A detailed investigation of the pH dependence was performed for 4,4′‐sulfonylbis[phenol] ( SBP ), bisphenol A (= 4,4′‐isopropylidenebis[phenol]; BPA ), and [1,1′‐biphenyl]‐4,4′‐diol ( BPD ). At pH ≥ pK_A of HO^. and H₂O₂, reactions between the model compounds and O₂^.? or ¹O₂ are the most probable ways to the phenoxy and ‘semiquinone’ radicals observed in this pH range in our EPR spectra. A large number of new radicals give evidence of multiple hydroxylation of the aromatic rings. Investigations at low pH are particularly relevant for understanding degradation in polymer‐electrolyte fuel cells (PEFCs). However, the chemistry depends strongly on pH, a fact that is highly significant in view of possible pH inhomogeneities in fuel cells at high currents. It is shown that also direct photolysis of the monomers leads to ‘semiquinone’‐type radicals. For SBP and BPA , this involves cleavage of a C? C bond.     

Polycrystalline Inorganic Fibers—Production,Properties, Applications

This progress report ends with the sentence: In the opinion of many experts, we are entering an “age of inorganic fibers”. An attempt is made in the article to outline the present stage of development and the outlook for one of the most interesting fields of modern materials science.     

Synthesis by Emulsion Polymerization of Poly(butyl acrylate-co-silver acrylate) Ionomers and Evaluation of their Possible Applications

The synthesis by emulsion polymerization and the characterization by a battery of techniques of poly(butyl acrylate-co-silver acrylate) [poly(BuAc-co-AgAc)] ionomers are reported here. Reaction rates were fast and conversions around 90% were obtained in less than one hour, regardless of the initial ratio of butyl acrylate and silver acrylate employed (BuAc/AgAc = 90/10, 80/20, 70/30). Particle size was in the range of 176 to 200 nm, depending on the BuAc/AgAc ratio. Ionomers’ formation was corroborated by infrared spectroscopy and inferred by differential scanning calorimetry (DSC). DSC disclosed that the poly(BuAc-co-AgAc) has two glass transition temperatures: one at ca. ?49°C due to relaxation of the ionomer backbone domains rich in BuAc and another ca. 35°C due to the relaxation of the backbone domains where the AgAc-units content was higher. Young moduli increased as the copolymers became richer in AgAc. Antibacterial tests against Escherichia coli with the 90/10 (BuAc/AgAc) ionomer revealed that the bacteria population diminishes from 5 log CFU/mL to less than 0.3 MPN/mL after one hour of contact with the ionomers. Also, we demonstrated that the ionomers are excellent compatibilizers for making semiconductive films of n-dodecylbenzene sulfonic acid-doped polyaniline (PANIDBSA)-poly(BuAc-co-AgAc) and poly(n-butyl methacrylate) (PBMA) blends. The electrical conductivity of the blend films, which were homogeneous, rose as the AgAc content in the films increased.     

PBMA-b-PSt磺化嵌段离聚体在DMF溶液中的聚集行为

采用激基缔合物荧光光谱法研究了轻度磺化聚甲基丙烯酸丁酯－b－聚苯乙烯（PBMA-b－PSt）嵌段离聚体在极性溶剂N，N－二甲基甲酰胺（DMF）溶液中的聚集行为；发现嵌段离聚体的磺化度和浓度强烈影响溶液中聚合物链的聚集态结构，不同的磺化度样品具有不同的临界聚集浓度；随磺化度增加，聚合物链缠绕密集，形成具有多苯环的聚集体，而且当磺化度为摩尔分数x＝3．59％时，荧光发射光谱最大发射峰波长出现最大红移，临界聚集浓度最低，说明最容易形成多苯环聚集体，该磺化点可以认为是磺化聚甲基丙烯酸丁酯－b－聚苯乙烯体现离聚体行为和聚电解质行为的临界磺化度。