Polyamides

The solubility of p-toluic acid (PTA) in acetic acid (HOAc) + water solvent mixtures was measured by a static method. The experimental temperature ranged from 303.2 to 363.2 K, and the mole fraction of acetic acid in the solvent mixtures ranged from 0.546 to 1.000. Together with the available solid−liquid equilibrium (SLE) data for ternary systems of terephthalic acid (TPA) + HOAc + H2O and benzoic acid (BA) + HOAc + H2O, the interaction parameters of the new UNIFAC group ArCOOH, defined as an aromatic group (Ar) plus an (aromatic) carboxyl group (COOH), with an aliphatic carboxyl group (COOH), methyl group (CH3 and CH2), aromatic group (Ar), aromatic methyl group (ArCH3), and water are determined. By using the new defined group ArCOOH, the UNIFAC model predicted SLE data for the above three ternary systems agree with the experimentally determined results satisfactorily.

Dynamic Light Scattering Study of Adsorption of a Nonionic Surfactant (C12E7) on Polystyrene Latex Particles: Effects of Aromatic Amino Groups and the Surface Polymer Layer

The grafting of copolymers has received significant attention due to the successful integration of their properties, both the backbone and graft chain polymers. The matter becomes even more interesting when the reactive/stimuli responsive polymeric chains are grafted onto backbone polymer, which offers unique physical properties such as crystallization or optoelectronic properties, etc. Such graft copolymer materials are very promising for the opening of new horizons of applications both in industry and academia. The grafting of reactive/responsive polymer chains onto commercially available polymers for greater manipulation of their properties is an attractive field of research. Grafting onto commercially available membrane-forming polymers such as poly(vinyledene fluoride) (PVDF) has aroused significant interest due to the possibilities of stimuli dependent membrane pore size modulation, supramolecular interactions have boosted its applications for affinity-based chromatography. Similarly, graft copolymers based on conjugated polymer backbones are also very much interesting, since interactions of the grafted chains with the external chemical or physical stimuli (such as pH, photoirradiation, salts, surfactants, temperature changes, etc.) significantly affect the conformation of the backbone chain, both in the solution state, gel state and solid state. This leads to changes in the optical response of the backbone polymers which are very useful in sensor applications, since the photo-responsivity of polymer systems is much stronger than small molecules due to signal amplification even under tiny perturbation. In most cases, grafting is done following an uncontrolled free radical-driven polymerization protocol, which associates threats to backbone degradation, the formation of high molecular weight graft chains, which affect the native properties of the backbone irreversibly. However, in order to keep the native properties of the backbone polymer intact, the grafting of polymeric chains must be performed in a controlled manner. In the present chapter, different strategies for the controlled grafting of neutral or ionic polymeric chains onto electroactive polymers and impact of the reactivity of the grafted chains onto the polymer property will be discussed.

Monobromo-, tetrabromo-, and pentachloro-corannulene are subjected to nucleophilic substitution reactions with tolyl selenide and phenyl telluride-based nucleophiles generated in situ from the corresponding dichalcogenides. In the case of selenium nucleophile, the reaction provides moderate yields (52-77 %) of the targeted corannulene selenoethers. A subsequent oxidation of the selenium atoms proceeds smoothly to furnish corannulene selenones in 81-93 % yield. In the case of tellurides, only monosubstitution of the corannulene scaffold could be achieved albeit with concomitant oxidation of the tellerium atom. Unexpectedly, this monotelluroxide derivative of corannulene (RR'Te=O, R=Ph, R'=corannulene) is observed to form a linear coordination polymer chain in the crystalline state. In this chain, Te-O constitutes the polymer backbone around which the aromatic groups (R and R') arrange as polymer side-chains. The polymer crystal is stabilized through intramolecular π-π stacking interactions of the side-chains and intermolecular hydrogen and halogen bonding interactions with the solvent (chloroform) molecules. Interestingly, each diad of the polymer chain is racemic. Therefore, in terms of stereoregularity, the polymer chain can be described as syndiotactic.

Self-assembly of rod–coil block copolymers

In order to investigate the steric effect of aromatic pendant groups and the electrical bistability in nonconjugated polymers potentially for memory device applications, two π-stacked polymers with different steric structures are synthesized and characterized. They exhibit two conductivity states and can be switched from an initial low-conductivity (OFF) state to a high-conductivity (ON) state. Additionally, they demonstrate nonvolatile write-once-read-many-times (WORM) memory behavior with an ON/OFF current ratio up to 10(4), and flash memory behavior with an ON/OFF current ratio of approximately 10(5). Both steady-state and time-resolved fluorescence spectroscopies are used to examine the conformational change of the polymers responding to an applied external electrical voltage. The results provide useful information on different steric effects of pendant groups in polymer chains, resulting in various electrical behaviors. The possibility in realizing an "erasable" behavior through breaking π-stacked structures of pendant groups by a reversal of the electric field was also discussed on the basis of temperature-dependent fluorescence spectroscopy investigation. These results may thus offer a guideline for the design of practical polymer memory devices via tuning steric structure of π-stacked polymers.

Intramolecular electron-transfer reactions in polymers with aromatic side groups were confirmed by the pulse radiolysis of solutions containing poly(4-vinylbiphenyl-co-1-vinylpyrene). First, the optical absorption spectra and decay reactions of the anions produced by electron pulses in 2-methyltetrahydrofuran containing homopolymers poly(4-vinylbiphenyl) or poly(1-vinylpyrene) were studied. Steady-state optical absorption spectra of these polymer anions produced by {gamma}-radiolysis at 77 K were also studied for comparison. Second, solutions containing the copolymers in which a small number of biphenylyl side groups of poly(4-vinylbiphenyl) were substituted by pyrenyl groups were examined. The transient absorption spectra observed by pulse radiolysis of these solutions clearly showed the existence of the intramolecular electron-transfer process along the polymer chain with the biphenylyl side groups as a stepping stone. The results were analyzed on the basis of a simple one-dimensional random-walk mechanism.

Thermoresponsive polymers in water, for example, poly(N‐isopropylacrylamide) (PNIPAM) are investigated extensively, due to a wide range of biomedical applications. However, the attempts to control thermoresponsiveness are still rare in less or nonpolar media. Herein, the three thermoresponsive homopolymers tethering an N‐butylurea group in the side chain with a different polymer backbone are reported. They exhibit lower critical solution temperature (LCST)‐type and upper critical solution temperature (UCST)‐type thermoresponsiveness depending on association of the urea group in the polymer chain and hydrogen bonding small molecules (effectors) in ternary systems (polymer/effector/organic solvent). The difference of polymer backbone appears as their change of solvophobicity in organic solvents. Poly(methacrylate) backbone needs more amount of the effector in nonpolar organic solvents, and poly(vinyl ether) backbone needs more amount in polar organic solvents. However, the influence of polymer backbone is too little to change the phase transition behavior, and the thermoresponsiveness is dominated by association and dissociation of hydrogen bondings between polymers and effectors. The supramolecular design of the thermoresponsive polymers is strong and extensible for the design of their phase transitions.

Summary form only given. Urethane substituted diacetylenes C/sub 4/[(CH/sub 2/)/sub n/OCONHCH/sub 2/COOC/sub 4/H/sub 9/]/sub 2/ (nBCMU) can be solid-state polymerised to high molecular weight polymer by high energy irradiation [1]. We have followed the change in conductive properties as polymerisation proceeds using the contactless pulse-radiolysis time resolved microwave conductivity (TRMC) technique [2]. With this technique we can study the conductivity of the polymer backbones unperturbed by the effects of domain boundaries or chain to chain transfer [3]. We find that the conductivity in the 3-, 4- and 9BCMU samples increases linearly with monomer to polymer conversion. The charge carrier mobilities within the polymer backbones were determined to be at least 10 cm/sup 2//Vs. Conductivity studies using the TRMC technique have also been carried out on 100% thermally polymerised single crystals of bis-p-toluenesulphonate diacetylene (PTS). A similar charge carrier mobility of at least 7 cm/sup 2//Vs was found. Additional evidence for charge transport along the polymer backbone was provided by an anisotropy ratio of 160 in favour of the conductivity in the direction of the backbones.

This Account details the use of building blocks known as iptycene units, which are particularly useful in the design of advanced materials because of their three-dimensional, noncompliant structures. Iptycenes are built upon [2,2,2]-ring systems in which the bridges are aromatic rings, and the simplest member of this class of compounds is triptycene. Iptycenes can provide steric blocking, which can prevent strong interactions between polymeric chromophores that have a strong tendency to form nonemissive exciplex complexes. Iptycene-containing conjugated polymers are exceptionally stable and display solution-like emissive spectra and quantum yields in the solid state. This application of iptycenes has enabled new vapor detection methods for ultratrace detection of high explosives that are now used by the U.S. military. The three-dimensional shape of iptycenes creates interstitial space (free volume) around the molecules. This space can confer size selectivity in sensory responses and also promotes alignment in oriented polymers and liquid crystals. Specifically, the iptycene-containing polymers and molecules align in the anisotropic host material in a way that minimizes the free volume. This effect can be used to align molecules contrary to what would be predicted by conventional models on the basis of aspect ratios. In one demonstration, we show that an iptycene polymer aligns orthogonally to the host polymer when stretched, and these structures approximate molecular versions of woven cloth. In liquid crystal solutions, the conjugated iptycene-containing polymers exhibit greater electronic delocalization, and the transport of excited states along the polymer backbone is observed. Structures that preserve high degrees of internal free volume can also be designed to create low dielectric constant insulators. These materials have high temperature stability (>500 degrees C) and hardness that make them potential interlayer dielectric materials for integrated circuits. In cases where the iptycene structures are less densely spaced along the polymer backbones, interlocking structures can be created. These structures allow for small interpolymer motions, but at large deformations, the steric clashes between iptycenes result in the transfer of load from one polymer to another. This mechanism has the ability to impart greater modulus, strength, and ductility. It is difficult to increase modulus without adversely affecting ductility, and classical high-modulus materials have low ductility. As a result, the use of interlocking iptycene structures is a promising approach to new generations of structural materials.

Results of recent time-of-flight transport measurements on the silicon backbone polymer poly(methylphenylsilylene) (PMPS) carried out over broad ranges of fields and temperatures described in much greater detail than heretofore. The relative effect of a series of chemical dopants in reducing the hole drift mobility of PMPS is correlated with their respective ionization potentials. Doping effects can be completely understood on the basis of a simple model which is described. Transport in PMPS manifests the key features observed in a broad class of polysilylenes containing aromatic and/or aliphatic side group substituents including those completely devoid of π electrons. Side-group substituents in saturated carbon backbone polymers such as poly(N-vinylcarbazole) completely dominate the transport process which is hopping between the carbazole chromophores. In contrast with this behaviour, comparative measurements indicate that side-group substituents in polysilylenes play a secondary role. The compl...

Natural fibers are gaining the interest of scientists and engineers in packaging, low cost housing and other general applications. In the present study, biodegradable property and swelling properties of different volume fraction of randomly distributed areca fibre and maize powder reinforced urea formaldehyde composites has been investigated. Areca fibres were chemically treated with dilute NaOH solution; composites were prepared by hydraulic hot press at 1400C and 2 MPa of pressure. Composites are cured under ambient conditions for 5 hours. The tests were conducted according to ASTM standards. The degradation involves bond scission reactions in the backbone of polymers, when the original form disappears. The composite absorbs some amount of moisture present in the compost in the early stages and there is an increase in the rate of the reaction between the enzymes secreted by the organism and the polymer chains or additives, which make up the compound. It is a very slow process since the areca fibers and maize powder do not decompose at a faster rate. It has been observed that at the initial stages the specimens shows increase in the weights for nearly one month and then starts loosing its weight showing the biodegradability. In swelling, it absorbs about 30-40 % of its thickness. Compared to conventional woodbased particle board it is very small where water absorption for wood-based particle board is more than 40%. Therefore this experiment shows that the composite made of areca fibers and maize powder have significantly less water absorption. KeywordsNatural fibers, urea formaldehyde resin, hybrid composite, volume fraction

Aromatic polyimides are one of the successful classes of synthetic polymers featuring high thermal stability, thermooxidative stability, low dielectric constants, excellent mechanical properties and chemical and solvent resistance, which are some of the reasons for the immense scientific and commercial interest in aromatic polyimides [1, 2]. Due to these superior properties, polyimides enjoy a wide range of application in different fields such as biomaterials, adhesives, gas separation membranes, composite matrices, coating and foams [3–6]. The prospects of synthesis and studies of extended rod-like or rigid aromatic polyimides have been extended due to their superior qualities. These include thermal stability, high modulus and high strength fibers, with low thermal expansion coefficient for packing in microelectronic applications [7]. However, the rigid, rod-like polyimides cannot be used as engineering materials as their poor solubility and processability hinders them to react below their decomposition temperature [8]. Various research efforts have been carried out to synthesize soluble polyimides in fully imidized form in such a way that their excellent properties are not compromised [9–11]. One of these investigations was the introduction of flexible segments [e.g. -O-, -SO2-, -CH2-, -C(CF3)2and –NHCO-] into the polymer chain. These groups provide kinks between the rigid phenyl rings in the backbone, and these lead to enhanced solubility of the polymer [12–17]. The replacement of symmetrical aromatic rings by unsymmetrical ones led to the reduction in crystallinity [18], while introduction of bulky lateral substituents (such as t-butyl, phenyl and adamantly groups) decreases the close-packing in the polymer backbone thus enhancing solubility of the polymer [19–22]. Besides the above applications, another striking reason for particular attention towards aromatic polyimides is that their thermal properties bear a close resemblance to a class of copolyimides called poly(amide-imide)s. Furthermore, the inclusion of an amide group into the polyimide backbone increases its processability, solubility and moldability [23]. In addition to this, poly(amide-imide)s have shown outstanding hydrolytic stability, excellent resistance to high temperature and promising balance of other physical and chemical properties [24]. Aromatic polymers with arylsulfone linkages are generally amorphous, have higher chain flexibility, lower glass transition temperatures and better tractability as compared to their corresponding polymers without these groups in the repeat units. The enhanced solubility and lower glass transition temperatures are credited to the flexible linkages that provide a polymer chain with a lower energy for internal rotation. Different disciplines such as sciences, medicine, material sciences and engineering functioned together to form the field of biomaterials [25]. The use of polymers as biomaterial is also known to the world. Biomedical polymers need to be biocompatible to avoid adverse biological effects to the nearby tissues and degradation of the ionic biological environment if exposed for a longer period [26]. G. Waris :H. M. Siddiqi (*) : Z. Akhtar Department of Chemistry, Quaid-i-Azam University, Islamabad, Pakistan e-mail: humaira_siddiqi@yahoo.com

The development of polymeric materials by high energy radiation processing has become very popular for their use in high-performance and advanced applications. Both the electron beam and gamma irradiation of different polymeric materials, e.g., single as well as multi-component systems (polymer blends, composites, and nanocomposites) have been studied for wire and cable, automotive, heat-shrinkable tube, aerospace, aircraft, transportation, agriculture, sports, biomedical, and nuclear applications. The grafting of monomer on the different polymeric backbones, intra- or interphase chain crosslinking, and scission in various polymer blends, composites and nanocomposites have been explored by electron beam and gamma radiation processing. Electron beam, or gamma radiation crosslinking improves the mechanical properties, chemical resistance, insulation, environmental resistance, thermal stability, and morphology of polymer blends and composites. This chapter focuses on the effect of gamma and electron beam irradiation on the grafting of functional monomer on the polymeric backbone, chain crosslinking, and end-use properties of polymer blends, composites, and nanocomposites. In this chapter, various polymeric multi-component systems have been studied using low-density polyethylene, high-density polyethylene, nylon-6, ethylene-propylene diene elastomer, ethylene vinyl acetate copolymer, polypropylene, and the effect of reinforcements such as fibers and fillers (clay, mica, and magnesium hydroxide) on property and application developments.

Facile preparation of degradable thermoresponsive polymers as biomaterials: Thermoresponsive polymers prepared by radical polymerization degrade to water-soluble oligomers