High Performance Polymers recent issues

On the 70th Anniversary of the Birth of Marc J.M. Abadie

Bruma, M. — Wed, 14 Oct 2009 02:22:15 PDT

New Sulfonated Polyethers and Polynaphthylimides based on TNT Derivatives

Wed, 14 Oct 2009 02:22:15 PDT

New sulfonated and non-sulfonated monomers — dinitro and diamino compounds — were prepared on the basis of 1,3,5-trinitrobenzene (TNB) which is the demethylation product of 2,4,6-trinitrotoluene (TNT). The sulfonated dinitrocompounds interacted with different binuclear bis-phenols under the conditions of aromatic nucleophilic nitrodisplacement reactions. Polyethers of moderate molecular weights were prepared on the basis of dinitrocompound containing electron-withdrawing 3,5-dinitrodiphenyl sulfone-4'-sulfonic acid "bridging" groups. Copolymers and blends with other sulfonated polymers were prepared to improve the film-forming properties of the polyethers developed on the basis of 3,5-dinitrodiphenyl sulfone-4'-sulfonic acid. High molecular weight sulfonated polynaphthylimides were prepared by the interaction of sulfonated diamine containing electron-donating ether group — 3,5-diaminodiphenyl ether-4'-sulfonic acid — with bis(naphthalic anhydride)s. The sulfonated polyethers and polynaphthylimides thus obtained contain sulfonic acid groups in the side chains.

Comparative Study of Polyimides Containing Oxadiazole and Ether Groups

Bruma, M., Damaceanu, M. D., Muller, P. — Wed, 14 Oct 2009 02:22:15 PDT

An aromatic diamine with a preformed oxadiazole ring and various dianhydrides with ether and other flexible or bulky groups, such as isopropylidene, hexafluoroisopropylidene, cyclohexylidene or fluorenylidene, were used in a polycondensation reaction at high temperature to produce poly(oxadiazole-ether-imide)s. The properties of these polymers such as solubility, film-forming ability, thermal stability and photoluminescence were studied and compared with those of related conventional aromatic polyimides. The mechanical properties of the free-standing films obtained from these polyimides were also investigated.

Aromatic Polyethers based on Meta-activated Dinitrocompounds

Rusanov, A. L., Komarova, L. G. — Wed, 14 Oct 2009 02:22:15 PDT

Aromatic polyethers containing phenyl sulfone side groups were prepared using aromatic nucleophilic nitrosubstitution reaction. As starting compounds TNT-derived 3,5-dinitrodiphenyl sulfone and 4,4'-bis-[(3-nitro-5-phenylsulfonyl)phenylsulfonyl]diphenyl sulfone containing functional nitro groups activated with electron-withdrawing phenylsulfone meta-substituents were used. Polymers obtained are soluble in wide range of organic solvents and demonstrate large ‘windows’ between their softening and degradation temperatures.

Glycidoxypropylsilane-functionalized Magnetite as Precursor for Polymer-covered Core-shell Magnetic Particles

Wed, 14 Oct 2009 02:22:15 PDT

Surface-functionalized core-shell magnetic particles were obtained by reacting the hydroxyl groups on the surface of pre-prepared magnetite particles with 3-glycidoxypropyltrimethoxysilane. Fourier transform infrared spectra indicated that epoxy silane molecules were chemically bound onto the surface of magnetite particles through Fe—O—Si linkages. As proved by atomic force microscopy and environmental scanning microscopy combined with energy dispersive X-ray spectroscopy, particles with average core diameter and shell width of about 700 and 70 nm, respectively, were obtained. The covered magnetite particles showed a lower saturation magnetization (46 emu g¹) as compared to the uncoated magnetite (64 emu g¹).

Study of the Behavior of Some Polyheteroarylenes Treated with Supercritical Carbon Dioxide

Ronova, I. A., Nikitin, L. N., Sokolova, E. A., Sava, I., Bruma, M. — Wed, 14 Oct 2009 02:22:15 PDT

Various polyheteroarylenes have been studied with regard to their physical properties before and after treatment with supercritical carbon dioxide (sc-CO₂). Thus, the study of dependence of glass transition temperature and free volume of polymer matrix on the conformational rigidity showed that the process of swelling in sc-CO₂ is influenced by the residual solvent and by the formation of possible hydrogen bonds between CO₂ and amide groups in the polymer chain.

Copolymers Obtained by {epsilon}-Caprolactam and Methyl Methacrylate Polymerization in the Presence of Polyimides

Wed, 14 Oct 2009 02:22:15 PDT

New copolymers have been synthesized by anionic or radical photopolymerization of -caprolactam or methyl methacrylate (MMA) in the presence of dissolved polyimides bearing hexafluoroisopropylidene, fluorene or other groups. Using diimides as models it was shown that the kinetics of anionic polymerization of -caprolactam depends on the nature of spacer between the imide cycles. The mechanical and tribological properties of copolymers, their water absorbance and the microstructure of copolymer films were studied. It was found that upon the selection of polyimide activator it was possible to gain the desirable control over the polymer properties, namely, the gel fraction content, phase composition, compression modulus, notched Izod impact strength, friction coefficient and temperature of frictional contact. The kinetics of radical polymerization of MMA in the presence of polyimide and model diimide has been studied by differential scanning photocalorimetry and infrared spectroscopy. From the results of the reaction kinetics and the study of polymer structures by Fourier transform infrared spectroscopy, nuclear magnetic resonance, size-exclusion chromatography and thermogravimetric analysis it has been established that radical photopolymerization of MMA in the presence of polyimide leads to the formation of copolymers owing to chain transfer reactions and/or chain termination by the relevant condensation polymer. It has been established that the imide cycles play a significant role in the formation of both copolymers with -caprolactam and MMA, respectively.

Poly[( N-Acylimino)ethylene] Derivatives for Advanced Materials

David, G., Simionescu, B. C. — Wed, 14 Oct 2009 02:22:15 PDT

New segmented polyurethanes containing soft and hard segments of different polarity and hydrophilicity, based on 4,4^'-methylenebis-(cyclohexyl isocyanate, 4,4^'-methylenebis-(phenyl isocyanate) and poly(tetramethylene oxide) or poly(ethylene oxide) were prepared including poly[(N-acylimino) ethylene] sequences as a chain extender. They were comparatively characterized by spectral, thermal and mechanical techniques. Some preliminary investigations on their nanocomposites with montmorillonite as an inorganic component are presented.

Dynamic Mechanical Analysis of Polyurethane-Epoxy Interpenetrating Polymer Networks

Cristea, M., Ibanescu, S., Cascaval, C. N., Rosu, D. — Wed, 14 Oct 2009 02:22:15 PDT

A series of semi-interpenetrated polymer networks based on bisphenol A epoxy resin and polyurethane was synthesized by sequential procedure. The molecular dynamics of polyurethane incorporated in the resin network with increasing amounts of resin was followed by dynamic mechanical analysis. All phenomena that concur in the material are evaluated by cross-examination of the storage modulus (E'), loss modulus (E'') and loss factor (tan ) variation with temperature. Complex aspects were elucidated in consecutive heating-cooling-heating cycles and by calculating the apparent activation energy of relaxations in multiplex experiments.

Mechanistic Aspects of Polynaphthalimide Synthesis from NMR Analysis

Piroux, F., Mercier, R., Picq, D. — Wed, 14 Oct 2009 02:22:15 PDT

The mechanism of the polycondensation reaction leading to naphthalimide polymers has been investigated using a model compound. In complement to ¹⁹F-NMR analysis, ¹H- and ¹³C-NMR spectroscopies were used to identify the intermediate compound. It was concluded that there was no evidence for the formation of an isoimide, but the formation of an amide—acid intermediate was clearly demonstrated.

Aspects of Morphology Control during the Oxidative Synthesis of Electrically Conducting Polymers

Schulz, B., Dietzel, B., Orgzall, I., Diez, I., Xu, C. — Wed, 14 Oct 2009 02:22:15 PDT

The formation of micro- and nanostructures during the oxidative polymerization of polypyrrole and polyaniline is investigated using different sulfonic acid dopants. Rod- or tube-like structures are found in polypyrrole as well as in polyaniline without addition of further compounds to the initial reaction mixture of monomer, dopant and oxidant. In these cases, always a crystalline precursor complex composed of a dopand molecule and the pure monomer (aniline) or a trimeric moiety (pyrrole) serves as in-situ template. In most cases the surface of the growing polymer is covered by secondary structures with much smaller sizes so that a hierarchical order of structures at different length scales results. Corresponding model considerations for the polymerization process are outlined. Additionally, unusual structures like platelets, frames, rings, or ribbons are observed in the polypyrrole synthesis in the presence of fluorosurfactants.

High Temperature VARTM of Phenylethynyl Terminated Imides

Wed, 14 Oct 2009 02:22:15 PDT

Depending on the part type and quantity, fabrication of composite structures using vacuum-assisted resin transfer molding (VARTM) can be more affordable than conventional autoclave techniques. Recent efforts have focused on adapting VARTM for the fabrication of high temperature composites. Due to their low melt viscosity and long melt stability, certain phenylethynyl terminated imides (PETI) can be processed into composites using high temperature VARTM (HT-VARTM). However, one of the disadvantages of the current HT-VARTM resin systems has been the high porosity of the resultant composites. For aerospace applications, the desired void fraction of less than 2% has not yet been achieved. In the current study, two PETI resins, LaRC PETI-330 and LaRC PETI-8 have been used to make test specimens using HT-VARTM. The resins were infused into ten layers of IM7-6K carbon fiber 5-harness satin fabric at 260 or 280 ^°C and cured at temperature up to 371 °C. Initial runs yielded composites with high void content, typically greater than 7% by weight. A thermogravimetric-mass spectroscopic study was conducted to determine the source of volatiles leading to high porosity. It was determined that under the thermal cycle used for laminate fabrication, the phenylethynyl endcap was undergoing degradation leading to volatile evolution. This finding was unexpected as high quality composite laminates have been fabricated under higher pressures using these resin systems. The amount of weight loss experienced during the thermal cycle was only about 1% by weight, but this led to a significant amount of volatiles in a closed system. By modifying the thermal cycle used in laminate fabrication, the void content was significantly reduced (typically ~ 3% or less). The results of this work are presented herein.

Polysulfone-based Ionomers for Fuel Cell Applications

Iojoiu, C., Sanchez, J.-Y. — Wed, 14 Oct 2009 02:22:15 PDT

This paper is a review that is focused on ionomers based on aromatic polysulfone backbone and intended to be used in proton exchange membrane fuel cells or in direct methanol fuel cells. Emphasis is placed on the different chemical routes to prepare the ionomers. Special attention is given to the impact of the ionomer structure on the conductivity performance and on the dimensional stability of the membranes at high temperatures.

Polydimethylsiloxane--silica Composites. Influence of the Silica on the Morphology and the Surface, Thermal, Mechanical Properties

Alexandru, M., Cazacu, M., Vlad, S., Iacomi, F. — Thu, 06 Aug 2009 08:04:28 PDT

A series of polydimethylsiloxane—silica composites each, with a different silica contents were prepared and investigated by multiple techniques: thermogravimetric analysis, X-ray diffraction, atomic force microscopy, contact angle measurements, and tensile strength tests, in order to evaluate some microscopic and macroscopic properties. As expected, the results show a dependence of the composites' properties on the silica content and their preparation procedure: in situ or ex situ. Whereas the dependence of the thermal and mechanical properties was expected and emphasized their improvement as the silica content increased, in the case of morphology and surface properties this dependence appeared to be more complex.

A Deep-Blue Electroluminescence from 2,5-Diphenyl-1,3,4-oxadiazole and Polyfluorene Copolymer End-capped with Triphenylamine

Ishii, J., Sunaga, T., Deguchi, S., Tsukioka, M. — Thu, 06 Aug 2009 08:04:28 PDT

An electron-transporting 2,5-bis(4-bromophenyl)-1,3,5-oxadiazole (OXD) was incorporated by copolymerization into polyfluorene (PF) end-capped with a 4-bromo-4',4"-dimethyltriphenylamine (TPA) main chains on the Yamamoto coupling method to improve the initial electroluminescence (EL) color stability against applied voltage and the device operation lifetime. The copolymer, PF/OXD-TPA, possessed a high molecular weight enough for film-forming ability and excellent solution-processability, that is, good solubility in common organic solvents such as toluene. An EL device fabricated using this copolymer as a polymeric emission layer allowed the generation of a strong deep-blue EL peaking at 424 nm with a comparatively high EL efficiency of 0.47 cd A^-1, and its color was extremely stable against applied voltage within 527 V. The incorporation of OXD units into the PF-TPA system also improved the operation lifetime, although it is not a practical level for displays. The results are probably attributed to the great roles of the incorporated OXD units for disturbing the formation of fluorene excimer sites and for tuning the hole/electron mobility balance..

Synthesis and Characterization of a New Methacrylate Polymer with Side Chain Benzofurane and Cyclobutane Ring: Thermal Properties and Antimicrobial Activity

Erol, I. — Thu, 06 Aug 2009 08:04:28 PDT

The synthesis of a new methacrylate monomer (Benzofuran-2-yl)(3-mesityl-3-methylcyclobutyl)- O-methacrylketoxime is described. The monomer was polymerized in 1,4 dioxane solution at 65 °C using azobisisobutyronitrile as an initiator. The monomer and its polymers were characterized by infrared, and ¹H-NMR spectroscopy. The glass transition temperature of the polymer was investigated by differential scanning calorimetry and the apparent thermal decomposition activation energies (E_d) were calculated by the Ozawa method using a Shimadzu thermogravimetric analysis thermobalance. The E_d were values were determined to be 231 kJ mol^-1. The antibacterial and antifungal effects of the momomer and its homopolymer were also investigated on various bacteria and fungi.

Thermal Degradation Kinetics of Aromatic Copolyamides Containing Phthalazinone Moieties

Liu, P.-T., Jian, X.-G. — Thu, 06 Aug 2009 08:04:28 PDT

The kinetics of thermal degradation of aromatic copolyamides containing phthalazinone moieties and ether linkages was studied at several heating rates by thermogravimetric analysis (TGA). The thermal-resistance properties of the new polymers did not decrease notably compared with Kevlar^®. The activation energy of the solid-state process was determined using the Kissinger, Friedman and Flynn— Wall—Ozawa methods, and the results indicate an activation energy of more than 160 kJ mol^-1. The results also show that the longer the flexible spacer in the monomer, the lower the thermal decomposition activation energy of the polymer, and that the presence of the phthalazinone structure increased the thermal decomposition activation energy of the polymers. The mechanism of thermal degradation was R deceleration type as determined by the Coats—Redfern method.

Synthesis and Characterization of bis (5-Cyanato Naphthalene-1 Oxy) Methyl Phenyl Silane Epoxy Composites

Thulasiraman, V., Sarojadevi, M. — Thu, 06 Aug 2009 08:04:28 PDT

A novel siloxane containing dicyanate was synthesized from the condensation reaction of dichloro methyl phenylsilane with 1, 5 dihydroxynaphthalene in a 1 : 2 ratio using triethylamine as catalyst. A new dicyanate was prepared by treating CNBr with synthesized silane containing diol in the presence of triethyl amine as catalyst at —10 to 5 °C. The dicyanate was characterized by Fourier transform infrared spectroscopy (FTIR) and NMR. The curing reaction of the prepared dicyanate and epoxy blends was studied using differential scanning calorimetry. The prepared dicyanate was blended with commercial epoxy resin in different ratios (3, 6 and 9%) and cured at 120 °C for 1 h, 150 °C for 1 h, 220 °C for 1 h using diamino diphenyl methane as the curing agent. The composite laminates with glass fiber were also fabricated using the same composition. Cured neat resin and epoxy blends were characterized by FTIR. The mechanical properties such as tensile strength, flexural strength, and fracture toughness of the composites were measured by adopting ASTM D 3039, D 790, and D 5528, respectively. The tensile strength increased with increasing cyanate content (3, 6, and 9%) from 55 to 62 MPa. Dynamic mechanical analysis shows that with increasing cyanate content in the composite the storage modulus moderately increased in comparison with the neat epoxy composite. There was not much difference in the values of storage modulus at 50 °C and that at 100 °C, showing that the synthesized cyanate has better thermo mechanical characteristics. The flame retardant property of epoxy—cyanate blend was observed to be 50, 36 and 25 s for 3, 6 and 9%, respectively, which showed that the silane-containing cyanate polymer had better flame retardant properties.

Functionalization of Poly(ether imide) Membranes via Surface-Initiated Atom-Transfer Radical Polymerization and their Use in Antifouling

Li, L., Yan, G., Wu, J., Yu, X., Guo, Q. — Thu, 06 Aug 2009 08:04:28 PDT

Poly(ether imide) (PEI) was chloromethylated by a simple one-step method under mild conditions to provide surface benzyl chloride groups as the active initiators for the surface-initiated atom-transfer radical polymerization (ATRP). Functional hydrophilic polymer brushes of poly(ethylene glycol) monomethacrylate and sodium 4-styrenesulfonate, as well as their block copolymer brushes, were synthesized via surface-initiated ATRP from the chloromethylated PEI membrane surfaces. The surface-modified membranes were studied by X-ray photoelectron spectroscopy. Using the bovine serum albumin solution adsorption test, the grafted PEI membranes showed great antifouling properties compared to the pristine PEI surface. Thus, the chloromethylated PEI membranes with the active ATRP initiators opens up opportunities for the functionalization of membranes via surface molecular design.

Electrical Transport Mechanism in Polyaniline/Formvar Blend Films

Ebrahim, S. — Thu, 06 Aug 2009 08:04:28 PDT

Polyaniline (PANI) was synthesized chemically and doped with camphor sulfonic acid. New PANI/formvar blend films were prepared using solution blending. These blend films were characterized by UV-visible, Fourier transform infrared spectra and scanning electron microscopy to investigate their optical, structural and morphological properties. It was found that the percolation threshold of these blend films is 4.4 wt.% of PANI. The dc and ac conductivities of these blend films were measured at a temperature range from 70 to 300 K in the frequency range of 10 kHz—1 MHz. The temperature dependence of the dc conductivity of the PANI/formvar blend films followed the three-dimensional variable range hopping. Temperature variation of frequency exponents in this blend suggests that ac conduction is attributed to be correlated to barrier hopping.

Synthesis of Proton-conducting Electrolytes Based on Poly(vinylidene fluoride-co-hexafluoropropylene) via Atom Transfer Radical Polymerization

Xiao, S., Chen, Y., Zhou, W., Qiu, J., Zhang, X. — Thu, 06 Aug 2009 08:04:28 PDT

The preparation of poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) grafted poly (styrene sulfonic acid) (PVDF-HFP-g-PSSA) copolymer as proton-conducting electrolytes by atom transfer radical polymerization of styrene sulfonic acid at the secondary halogenated sites of PVDF-HFP was demonstrated. The structure of the PVDF-HFP-g-PSSA copolymers was verified by Fourier transform infrared spectra, proton nuclear magnetic resonance spectra and X-ray photoelectron spectroscopy. The PVDF-HFP-g-PSSA copolymer membranes showed ion exchange capacity values ranging from 0.045 to 0.272 mEq g^-1, the water uptake varied from 13.7 to 26.8 wt.% and the proton conductivities varying from 1.85 2 10^-4 to 9.8 2 10^-4 S cm^-1, all of which could be modulated by control of the polymerization time. All the membranes exhibited decomposition temperature up to around 350 °C as revealed by thermogravimetric analysis. The incorporation of poly(styrene sulfonic acid) into PVDF-HFP chains resulted in melting at higher temperatures. The scanning electron microscopy observation indicated that the density of the ionic pathways increased with ionic content, which explained why the ionic conductivity rose to relatively high values as polymerization time increasing.

Erratum

Wed, 02 Sep 2009 02:55:18 PDT

Erratum

Wed, 02 Sep 2009 02:55:18 PDT

Erratum

Wed, 02 Sep 2009 02:55:19 PDT

Synthesis and Properties of a Liquid Crystalline Thermoset Epoxy Resin Containing 1,3,4-Oxadiazole Groups

Balamurugan, R., Kannan, P. — Fri, 22 May 2009 06:32:02 PDT

A new liquid crystalline thermoset (LCT) based on 1,3,4-oxadiazole was prepared from liquid crystalline epoxy resin containing oxadiazole and diaminodiphenyl methane. The LCT was characterized and compared with the conventional thermoset. The Time—Temperature Transformation diagram was constructed to determine an appropriate set of cure cycles. The goal of this paper was centered on the evaluation of the mechanical performances of this new class of thermoset. In the case of LC thermoset, a higher T_g and good fracture resistance were noticed than that of the conventional thermoset. The LC thermoset exhibited higher thermal stability when compared with the conventional non-LC thermosets. The results tempted to consider the LCT materials as potential candidates for advanced composites.

Novel Poly(amideimide)s: Synthesis, Thermal, and Optical Characterization

Grabiec, E., Schab-Balcerzak, E., Domagala, W., Kurcok, M. — Fri, 22 May 2009 06:32:02 PDT

A series of new aromatic poly(amideimide)s is synthesized via one-step high- temperature polycondensation from prepared diamidedianhydrides and various diamines: 4,4'-(hexafluoro-isopropylidene)dianiline, 4,4'-(9-fluorenylidene)dianiline, 2,7-diaminofluorene and 2,4-diamino-6-phenyl-1,3,5-triazine. Molecular and structural characterization of the resulting polymers is carried out using Fourier transform infrared and nuclear magnetic resonance spectroscopies. The resulting polymers exhibit a good level of thermal stability. The temperature of 10% weight loss is in the range of 420—525 °C (in N₂) associated with relatively high glass transition temperatures (249—299 °C). The polymers' residual weight loss at 800 °C is higher than 40%. The optical and photoluminescence characteristics of synthesized poly(amideimide)s were investigated in solution and in blend with poly(methylmethacrylate) (PMMA). The photoluminescence spectra of the polymers in N-methyl-2-pyrrolidinone solution exhibit maximum emission wavelength in the range of 405—495 nm depending upon the polymer structure.

Polyimides Containing Trans-1,4-cyclohexane unit (III). Ordered Structure and Intermolecular Interaction in s-BPDA/CHDA Polyimide

Fri, 22 May 2009 06:32:02 PDT

Polyimide (PI) derived from 3,3',4,4'-biphenyltetracarboxylic dianhydride (s-BPDA) with trans-1,4-cyclohexanediamine (CHDA), i.e., s-BPDA/CHDA was investigated from the viewpoint of ordered structure and intermolecular interaction. Thermodynamic parameters of the model compounds for melting behavior suggested significantly restricted conformational changes in the trans-1,4-cyclohexylene unit and the presence of strong BPDI—BPDI interaction in s-BPDA/CHDA. The effect of diamine structure on the fluorescence yield also supported the presence of the BPDI—BPDI interaction or the BPDI dimer in s-BPDA-based semi-cycloaliphatic PIs. The results of the fluorescence depolarization measurements can be rationalized by a proposed mechanism assuming the presence of the BPDI dimer sites, where the fluorescence of s-BPDA/CHDA occurs by excitation of the lower energy trap sites consisting of the BPDI dimer via excitation energy migration or direct excitation of the dimer. The structure-sensitive infrared band around 550 cm^-1 gradually shifted toward higher frequency with simultaneous narrowing with increasing cure temperature, suggesting gradual ordered structure formation in s-BPDA/CHDA. Thermal imidization at 400 °C caused splitting of the C—H stretching band around 2940 cm^-1, corresponding to the disappearance of distinct glass transition for the s-BPDA/CHDA system.

Synthesis of Hyperbranched Conjugated Copolymers Containing Triphenylamine and Fluorene or Thiophene Moieties

Grigoras, M., Stafie, L. — Fri, 22 May 2009 06:32:02 PDT

Novel hyperbranched conductive copolymers containing 4,4',4'' trisubstituted triphenylamine and 2,7-(9,9'-dioctyl)fluorenyl or 2,5-thienyl moieties were synthesized by palladium catalyzed cross-coupling reaction of bis boronic acids of fluorene or thiophene with tris(4-iodophenyl)amine, in an one-step process. The copolymers were obtained as fully or partially soluble materials in chlorinated or aprotic polar solvents, depending on the monomer structure and concentration and polycondensation time, and were characterized by Fourier transform infrared, ¹H-NMR, UV-vis and fluorescence spectroscopy.

Structural Rigidity of Aromatic Polyamides with Bulky Lateral Substitutions

Fri, 22 May 2009 06:32:02 PDT

In the present study the effect that controlled structural modifications have on the physical and conformational properties of a series of isomeric aromatic polyamides synthesized with different bulky pendant lateral groups was investigated. Physical properties of the aromatic polyamides such as thermal properties were determined by differential scanning calorimetry. Structural changes were determined by Fourier transform infrared spectroscopy, density and fractional free volume (FFV). Light scattering and dynamic-mechanical analysis were used to characterize the thermodynamic and kinetic rigidity. Vogel's model was applied to evaluate kinetic rigidity in polyamide chains and the results were compared with physical properties data. It was found that there was a relationship between T_g and the conformational entropy determined by the structure which indicates that the higher the level of rigidity in the polyamide the higher the value of T_g. For kinetic rigidity, it was found that the relaxation time at infinite temperature B , was very close to the value 5 x 10^-12 s, reported for other amorphous glassy materials. There was also a relationship between the activation energy of the glass transition U and FFV, which is determined by the presence or absence of the bulky functional groups, indicating that the smaller the FFV, the higher the energy required for the glass transition to take place.

Azopolysiloxanes Modified with Nucleobases: 1. Thermal Characterization of some Nanostructurable Materials with Potential Application in Biology

Lisa, G., Enea, R., Hurduc, N., Hurduc, N. — Fri, 22 May 2009 06:32:02 PDT

New azopolysiloxanes modified with nucleobases with potential application in biology were synthesized and their thermal stability was evaluated. These types of materials can present two possible applications: obtaining of films with nanostructured surface that may be used in cell directional development control and in biomolecular binding and nanohandling. Both applications involve, however, material interaction with laser beams, which require a series of precautions with regard to polymer thermal stability. We considered it essential to perform very thorough thermal stability studies that would provide accurate information concerning the lowest temperature at which thermal degradation occurred. Some correlations between structure—thermal stability were derived.

Effect of Composition and Hard-segment Content on Thermo-mechanical Properties of Cross-linked Polyurethane Copolymers

Oprea, S. — Fri, 22 May 2009 06:32:02 PDT

Polyurethanes (PUs) prepared by varying the hard-to-soft segments ratio, and the chain extender size and nature were studied. Polyurethane cross-linked copolymers composed of 4,4'-methylenebis(phenylisocyanate), poly(ethylene adipate)diol, and glycerine, 1,3 propanediol, 1,4-butanediol, 1,6-hexanediol as a chain extender were synthesized by a two-step process. In the present study, cross-linked poly(ester-urethanes) were prepared with hard segment contents from 22 to 44% by weight, by systematically varying the ratio of the hard-segment extender. Hard segment content has a significant influence on the mechanical and thermo-mechanical properties of PUs, such as maximum stress, tensile modulus, and elongation at break. In particular, maximum stress, tensile modulus, and elongation at break increased significantly at 24 wt.% of hard segment content. Interchain crosslinking improves thermal stability, which was measured by thermogravimetric analysis and differential scanning calorimetry. In contrast with glassy shape memory polymers, chemically cross-linked polyurethane behaves as an elastomer capable of shape memory.

Erratum

Fri, 22 May 2009 06:32:02 PDT

Organo-Soluble Low CTE Polyimides and their Applications to Photosensitive Cover Layer Materials in Flexible Printed Circuit Boards

Ishii, J., Akamatsu, T. — Tue, 10 Mar 2009 08:48:22 PDT

A novel cover layer material for flexible printed circuit (FPC) applications was developed in this work. A high molecular weight of polyimide composed of four monomers, pyromellitic dianhydride (PMDA), 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA), 2,2'-bis(trifluoromethyl)benzidine (TFMB) and 2,2-bis(3-amino-4-hydroxyphenyl)hexafluoropropane (BisApAf) was prepared by the one-pot polycondensation in N-methyl-2-pyrrolidone (NMP) without precipitation and gelation. The polyimide (PI) was highly soluble in various common organic solvents. Interestingly, the PI film formed by simple solution-casting of the PI solution had a low CTE value close to that of copper foil, therefore almost no curling of the PI/copper laminate was observed when the PI film was directly formed on a copper foil. The PI film also exhibited other combined properties, including a low CTE, a high T_g, high thermal stability, low water absorption, comparatively good transparency, the highest levels of non-flammability, good insulation properties and sufficient film flexibility. In addition, fine positive-tone patterns could be obtained from DNQ-containing PI with a sensitivity of 238 mJ cm^-2. The results revealed that the present PI system is a promising candidate as a novel cover layer material.

Synthesis and Characterization of Benzylidene and Azobenzene Based Photochromic Liquid-Crystalline Polymers

Jayalatha, D., Balamurugan, R., Kannan, P. — Tue, 10 Mar 2009 08:48:22 PDT

Two series of novel thermotropic main chain liquid crystalline polymers containing photocrosslinkable chalcone and photoisomerizable azobenzene moieties were synthesized from bis[4-(m-hydroxyalkoxy)benzylidene]cycloalkanones [m = 6,8,10] with 4,4'-azobenzene dicarbonylchloride. The chemical structure of the monomers and polymers were confirmed by spectral techniques. The mesophase properties were investigated using hot stage optical polarized microscopy and differential scanning calorimetry. All the polymers exhibited liquid crystalline properties. The thermogravimetric analysis data revealed that the polymers were stable up to 220 °C and underwent two-stage decomposition. Photocrosslinking property of the polymers was investigated using UV spectroscopy. The cyclopentanone containing polymers showed faster photocrosslinkability than that of their cyclohexanone counterpart. In addition to the photocrosslinkability of cycloalkanone units, the azo moiety displayed E-Z (trans-cis) isomerization in the polymer backbone.

Preparation, Properties, and Mechanism of Novel Polyurethane Adhesive/Organic Montmorillonite Nanocomposites

Jincheng Wang, , Yuehui Chen, , Yuan Tang, , Minming Xu, — Tue, 10 Mar 2009 08:48:22 PDT

Novel polyurethane adhesives (PUA) were prepared by the incorporation of organic montmorillonite (OMMT). The structure of the PUA/OMMT adhesives was analyzed by wide angle X-ray diffraction, Fourier transform infrared spectroscopy, and transmission electron microscopy. It was observed that the OMMT layers in the PUA were of nanometer dimensions and the molecular structure of PUA was perturbed by the presence of OMMT. This was due to the reaction between the monomers and the intercalation agent. Physico-mechanical properties such as adhesion and thermal stability were investigated. Results showed that the PUA system with 3 phr OMMT has the best physical and mechanical properties due to the exfoliation of OMMT. The nano-reinforcing effect caused by the exfoliated silicate layers may reduce the amount and size of voids during peeling, which can increase the length of the crack path in their vicinity, leading to improved adhesive properties. This is postulated as the mechanism for improved adhesion in the PUA/OMMT adhesive.

Synthesis and Characterization of New Fluorinated Polyimides derived from 9, 10-bis[3'-trifluoromethyl-4' (4''-aminobenzoxy) benzyl] Anthracene

Ghosh, A., Banerjee, S. — Tue, 10 Mar 2009 08:48:22 PDT

A new diamine monomer 9,10-bis [3'-trifluoromethyl-4'(4''-aminobenzoxy) benzyl] anthracene (TFAA) was synthesized that led to a number of novel fluorinated polyimides by thermal imidization route when reacted with different commercially available dianhydrides such as 4,4'-(4,4'-isopropylidenediphenoxy)bis(phthalic anhydride) (BPADA), 4,4'-oxydiphthalic anhydride (ODPA), 4,4'-(hexafluoroisopropylidene) diphthalic anhydride (6FDA) and 1,2,4,5-benzenetetracarboxylic dianhydride (PMDA). These polyimides showed very high thermal stability with decomposition temperature (5% weight loss) 500— 550 °C in nitrogen depending on the exact structure. Transparent thin films of these polyimides exhibited tensile strengths of 40—74 MPa, a modulus of elasticity 2.33—2.9 GPa and elongation 5—10% depending on the exact polymer structure. Except for the polymer derived from PMDA, these polymers exhibited good solubility in common organic solvents. The polyimides showed absorbance spectra in the visible region and broad peak in photoluminescence spectra.

Synthesis and Properties of Novel Meltable Fluorinated Aromatic Oligoimides Endcapped with 4-Phenylethynylphthalic Anhydride

Jiansheng Chen, , Hongjun Zuo, , Lin Fan, , Shiyong Yang, — Tue, 10 Mar 2009 08:48:22 PDT

A series of phenylethynyl-endcapped fluorinated aromatic oligoimides with calculated molecular weights of 1250—10000 were prepared by thermal polycondensation of an aromatic dianhydride, 4,4'oxydiphthalic anhydride (ODPA), with aromatic diamine mixtures of 1,4-bis(4-amino-2-trifluoromethylphenoxy)-benzene (1,4,4-6FAPB) and 3,4'-oxydianiline (3,4'-ODA) in the presence of 4-phenylethynylphthalic anhydride (PEPA) as reactive endcapping agent. Effects of chemical compositions and molecular weights of the aromatic oligoimides on their meltability as well as the thermal and mechanical properties of the thermal-cured polyimide resins were systematically investigated. The phenylethynyl-endcapped fluorinated aromatic oligoimides could be completely melted in the temperature range of 250—350 °C to give low viscosity fluids. The melt viscosity of the oligoimide increased with increasing molecular weight. After thermally curing at 371 °C, the thermoset polyimide resins produced showed good combination of thermal and mechanical properties. For example, the glass transition temperature (T_g) as high as 300 °C by differential scanning calorimetry, flexural strengths of > 135.5 MPa, flexural moduli of > 3.1 GPa, tensile strength of > 65.7 MPa and elongation at break of > 3.9% were obtained.

Aromatic Poly(ether imide)s Containing Nitrile Groups

Hamciuc, C., Hamciuc, E., Ignat, M., Zarnescu, G. — Tue, 10 Mar 2009 08:48:22 PDT

A novel series of organosoluble poly(ether imide)s containing nitrile groups was prepared by solution polycondensation reaction of an aromatic diamine, namely 4-[bis(4-aminophenyl)amino]benzonitrile with different aromatic bis(ether anhydride)s, such as 2,2-bis[(3,4-dicarboxyphenoxy)phenyl]propane dianhydride, 1,1,1,3,3,3-hexafluoro-2,2-bis[(3,4-dicarboxyphenoxy)phenyl]propane dianhydride, 2,2'-bis[(3,4-dicarboxyphenoxy)phenyl]-1,4-phenylene-diisopropylidened dianhydride, 1,1-bis[(3,4-dicarboxyphenoxy)phenyl]cyclohexane and 9,9-bis[(3,4-dicarboxyphenoxy)phenyl]fluorene dianhydride. The polymers were readily soluble in polar organic solvents, such as N-methyl-2-pyrrolidone and N,N-dimethylformamide as well as in less polar organic solvents such as chloroform, and could be cast from solution to form thin flexible films. The gel permeation chromatography measurements revealed that the polymers had number-average and weight-average molecular weights up to 58 000 and 100 000 g mol^-1, respectively. Their inherent viscosities were in the range of 0.37—0.67 dL g^-1 . Thermogravimetric analysis showed that all polymers were stable up to 500 °C with 10% weight losses recorded from 535 to 600 °C in air. The polymers exhibited a glass transition in the temperature range of 224—279 °C, with reasonable interval between glass transition and decomposition temperature. A composite film based on a poly(ether imide) and pyrite ash powder was prepared and its nanoactuation was investigated.

Highly Tough and Highly Transparent Soluble Polybenzoxazoles (II): Effect of Sulfone Group

Miyazaki, T., Hasegawa, M. — Tue, 10 Mar 2009 08:48:22 PDT

Novel semi-cycloaliphatic (semi-alicyclic) colorless polybenzoxazoles (PBOs) were polycondensed from 3,3'-diamino-4,4'-dihydroxydiphenylsulfone (ABPS) with several cyclohexanedicarboxylic acid (CHDCA) isomers in poly(phosphoric acid) (PPA) at an elevated temperature. The PBO system derived from ABPS with 1,4-CHDCA (trans/cis mixture) possessed excellent combined film properties, i.e., a very high T_g at 294 °C, high transparency (transmittance = ca. 80% at 400 nm for 20 µm thick film), high thermal stability (5% weight loss temperature, T⁵_d > 400 °C in an air atmosphere), sufficient film toughness (elongation at break, E_b > 20%), and good solubility in a variety of common organic solvents (good solution-processability) except for a drawback, a relatively high water absorption (W_A = ca. 2%). The influence of synthetic route on the film properties was also investigated in a comparison with the same chemical composition of PBO film prepared via the two-step method, namely, thermal cyclodehydration of its precursor (polyhydroxyamide). The results revealed that the PBO obtained from the one-pot PPA method is much more profitable from the viewpoints of higher film transparency than that from the two-step way. This result was discussed on the basis of the difference of the polymerization mechanisms. The properties of the colorless PBOs were also compared with those of the corresponding sulfone-containing semi-cycloaliphatic polyimide and poly(ether sulfone) as a typical high temperature engineering plastic. Copolymerization using minor fractions of 2,2-bis(3-amino-4-hydroxyphenyl) hexafluoropropane (BAHP6F) into the ABPS-based PBO system enabled us to reduce significantly the water absorption (W_A = 0.83%) without sacrificing other target properties. The colorless PBO developed in this work is a promising candidate as a new type of high-temperature plastic substrate materials for realizing flexible LCDs.