bluuebunny/crossref_metadata_2025 huggingface dataset:
Synthesis of novel graft polyhydroxyalkanoates
Authors: Renard Estelle , Tanguy Pierre‐Yves , Samain Eric , Guerin Philippe
Published: August 2003

Graft copolymers were synthesized by direct condensation of methoxy‐poly(ethylene glycol) (MePEG) or methoxy‐poly(lactic acid) (MePLA) onto a reactive polyhydroxyalkanoate (PHA) backbone in organic solvent. Side carboxylic groups of the PHA were coupled with end hydroxyl groups of MePEG or MePLA in the presence of N,N′‐dicylohexylcarbodiimide (DCC). Graft copolymers were characterized by 1H NMR spectroscopy and size exclusion chromatography (SEC). NMR spectra of PHA‐g‐PEG and PHA‐g‐PLA showed the presence of significant amounts of PEG and PLA, respectively. No noticeable unreacted PEG or PLA were detected in SEC chromatograms. Grafting of hydrophilic polymers chains as PEG or biodegradable oligomers as PLA onto PHA backbone will generate polyesters with a more rapid water uptake and faster biodegradation rates. These PHA polymers conjugates could be interesting for bioactive agent delivery systems.
Mechanical and thermal properties of poly(3‐hydroxybutyrate) blends with starch and starch derivatives
Authors: Innocentini‐Mei Lucia H. , Bartoli Julio R. , Baltieri Rodrigo C.
Published: August 2003

Poly(3‐hydroxybutyrate) (PHB) is a highly crystalline, biodegradable and biocompatible thermoplastic. However, its limited utilization as a commodity plastic is associated to both high cost and very poor mechanical properties. Blending PHB with a natural polymer, such as starch, is one way to improve its properties and to get low price raw materials, though they are not miscible since there are no strong interactions between the hydrophilic starch and the hydrophobic PHB. In this study binary blends of PHB were prepared with natural starch, starch‐adipate and grafted starch‐urethane derivatives. The PHB blends were characterized in terms of their mechanical and thermal properties. For all blends a decrease of the Young modulus was observed as compared to the pure PHB. However, blends containing natural starches and starch adipate resulted in brittle materials. A significant decrease of both glass transition temperature (Tg) and melting point (Tm) was observed for all formulations. The best results, lower modulus and Tg were obtained with grafted starch‐urethane blends using poly(propylene glycol).
Aqueous phase size exclusion chromatography of polyvinylalcohols of different degrees of hydrolysis
Authors: Lacík Igor , Šnauková Radka , Šimková Barbora , Hanzelová Silvia , Alexy Pavol
Published: August 2003

The aqueous‐phase size exclusion chromatography (SEC) represents a suitable method for the analysis of molecular weight distribution (MWD) of polyvinylalcohols (PVOHs) of different degree of hydrolysis ranging from 72 to 98 mol‐% applying the Suprema columns. Eluents of different composition were used consisting of either a mixture of water and acetonitrile for the lower degrees of hydrolysis (72 ‐ 88 mol‐%) or 0.1 M LiNO3 solution for the higher degrees of hydrolysis (88 ‐ 98 mol‐%). By knowing the M̄w̄ values of commercially available PVOHs samples of a given degree of hydrolysis and using the commercial water soluble narrow distribution standards, a principle of the constant hydrodynamic equivalence ratios was applied to obtain the absolute values of the molecular weights of PVOHs of different degree of hydrolysis. The effect of a various number of extrusion cycles on MWD of different PVOHs was used to demonstrate the sensitivity of the selected SEC conditions.
Characteristics and degradation of hybrid composite films prepared from PVA, starch and lignocellulosics
Authors: Cinelli Patrizia , Chiellini Emo , Gordon Sherald H. , Imam Syed H.
Published: August 2003

A research cooperation between USDA and the University of Pisa led to the development of several composite blends of poly(vinyl alcohol) (PVA) and lignocellulosic fibers. The cast films were prepared by blending orange fibers (OR‐fibers) and PVA with and without cornstarch to yield flexible and cohesive films. To improve properties, films were also prepared by crosslinking PVA, starch and OR‐fibers with hexamethoxymethylmelamine (HMMM). Films were evaluated for their thermal stability, water permeability and biodegradation. Thermal gravimetric analyses indicated the potential usefulness of such blends in several thermoplastic applications. Films were permeable to water, and retained the moisture content in the soil while retaining their integrity. Films generally biodegraded within 30 days in compost, achieving between 50‐80% mineralization. Both neat PVA and blends that had been crosslinked showed comparatively slow degradation. A possible stimulating effect of lingocellulosic fillers on the biodegradation of PVA in blends has been observed.
Thermoplastic processing of protein‐based bioplastics: chemical engineering aspects of mixing, extrusion and hot molding
Authors: Pommet Marion , Redl Andréas , Morel Marie‐Hélène , Domenek Sandra , Guilbert Stéphane
Published: August 2003

Proteins, as heteropolymers, offer a large range of possible interactions and chemical reactions. The thermoplastic behavior of proteins has been studied in order to produce bioplastics by thermal or thermomechanical processes such as mixing, extrusion or hot molding. The extrusion trials were performed by using a co‐rotating twin‐screw extruder, recording torque, temperature and die pressure. Batch mixing was done in a two blade counter‐rotating mixer, with continuous recording of torque and product temperature. Proteins were alternatively extruded, mixed or hot molded under a large range of processing conditions. Protein aggregation during each process was estimated from the accumulation of SDS‐insoluble protein fraction.

Protein aggregation evidences a cross‐linking reaction the activation energy of which was dependent on the thermoplastic process used. The increase in network density appears to be induced by the severity of the treatment: temperature and shear strongly affect the structural characteristics of the protein‐based bioplastics.
Novel blends from agave fibers and poly(methyl methacrylate)
Authors: Koschella Andreas , Heinze Thomas , Rivera Armenta Jose Luis , Mendoza Martinez Ana Maria
Published: August 2003

Cellulose‐rich fibers were isolated from Agave lechuguilla (AL) and Agave fourcroydes (AF) growing in the Mexican northeast. These fibers are a valuable feedstock for the preparation of blends with synthetic polymers like poly(methyl methacrylate), PMMA. Blends of different types of agave fibers (dewaxed, mercerized, and grafted) and PMMA were prepared and investigated by means of tension measurements and dynamic mechanical analysis. The fiber‐containing blends are more stable than the plain PMMA. Surprisingly, the mechanical stability of the blends is practically independent of the pretreatment of the fibers.

Methyl methacrylate (MMA) was grafted onto the biopolymer fibers initiated by the cerammonium nitrate redox initiator. Grafting yields of 26.5% were realized with fibers from AL while up to 75.8% MMA was grafted onto fibers from AF. The materials were characterized by means of FTIR spectroscopy and DSC.
Unconventional cellulose products by fluorination of tosyl cellulose
Authors: Koschella Andreas , Heinze Thomas
Published: August 2003

The synthesis of novel deoxy‐fluoro cellulose derivatives obtained by nucleophilic displacement reactions (SN) of p‐toluenesulfonyl (tosyl) cellulose with tetrabutylammonium fluoride (TBAF) is described. Detailed studies concerning the influence of the reaction time and temperature as well as the water content of the TBAF on the composition of the products were carried out. The SN reaction occurs even at room temperature. The degree of substitution of deoxy‐fluoro moieties (DSF) is in the range from 0.22 to 0.47. The polymers contain remaining tosyl groups. Preliminary 19F NMR measurements reveal the presence of the CH2F group. The degradation temperature of the deoxy‐fluoro cellulose derivatives is increased compared to the starting tosyl cellulose, however, a distinct influence of the remaining tosyl groups appears.
Multifunctional polyesters as new candidate materials for biomedical applications. Synthesis and structural characterization
Authors: Signori Francesca , Solaro Roberto , Chiellini Emo , Lips Priscilla A.M. , Dijkstra Pieter J. , Feijen Jan
Published: August 2003

The present work was aimed at the development of functional polymeric materials to be used in the targeted delivery of proteic drug and tissue engineering fields. The adopted strategy was based on the design of special polymer classes whose structures and functionality could be easily modified by finely tuned synthetic procedures. Poly(ether ester)s containing H‐bonding units were chosen as promising materials for the proposed applications. Commercially available precursors were successfully used for the synthesis of symmetrical diesters containing different H‐bonding groups (amide, carbamate, and urea moieties). In all cases, pure products were obtained in good yields. Bulk polycondensation of the monomeric precursors with different mixtures of 1,4‐butanediol and PEG 1000 diol afforded a variety of high molecular weight polymeric structures. Physical‐chemical characterization of the polymers indicates that their thermal, mechanical, and swelling properties can be tailored by a proper selection of the H‐bonding group and of the composition of the feed mixture.
An investigation of the condensation kinetics in poly(ester‐amide) and poly(ester‐sulphide) preparation
Authors: Solaro Roberto , Bizzarri Ranieri , Chiellini Emo
Published: August 2003

Synthetic processes leading to hydrophilic biodegradable polymers for bio‐inspired applications were investigated from a kinetic point of view. In accordance with the reported mechanism of ester aminolysis, polycondensation reactions of α‐amino‐ω‐esters, diesters, and diamines resulted markedly dependent on the basicity of the alkoxide leaving‐group, being relatively fast for penthachlorophenate monomers. Furthermore, experimental data concerning the homopolycondensation of penthachlorophenyl α‐amino‐ω‐oligo(ethyleneglycol) succinates of different degree of oligomerization clearly showed the existence of concurrent first and second‐order processes, which were attributed to the intramolecular cyclization and intermolecular polycondensation reaction, respectively. In contrast to theoretical predictions based on the collision theory, however, minor incidence of the cyclization reaction was shown by the shortest monomers, thus suggesting a significant kinetic effect due to steric hindrance and solvent‐reagent interactions. Analysis of the base‐catalyzed Michael‐type addition of α,ω‐oligo(oxyethylene)dithiols to methyl (meth)acrylate allowed for the optimization of the relevant polymerization process involving hydrophilic diacrylates. Interestingly, very low reaction rates were determined for methacrylic components, supposedly because of steric and electronic factors connected to the presence of the α‐methyl group. Minor effects on the reaction rate were also induced by solvent polarity and catalyst nature.
Polymeric nanoparticles based on polylactide and related copolymers
Authors: Chiellini Emo , Covolan Vera L. , Orsini Lorenzo M. , Solaro Roberto
Published: August 2003

The preparation of nanoparticle suspensions was carried out by using commercial biodegradable polymers as poly(d,l‐lactide), poly(d,l‐lactide‐co‐glycolide) and poly(d,l‐lactide‐co‐ϵ‐caprolactone). The method of preparation was based on the controlled addition of polymer organic solution to an aqueous phase containing dispersing agents. Poly(ethylene glycol) (10, 20, and 35 kDa grade), Tween 20, and Pluronic F‐127 were used as dispersing agents in the aqueous phase. Content and type of both polymeric matrix and dispersing agent resulted of paramount relevance for the attainment of monodispersed nanoparticles with average diameter of about 130 nm. The addition of a steric stabilizer allowed for nanoparticle purification and isolation while preventing their agglomeration. The best results were obtained by using 35 kDa grade poly(ethylene glycol) as dispersing agent and either mannitol or glycidylisopropylidenglyceryl‐β‐cyclo‐dextrin as steric stabilizer. The adopted procedure afforded biodegradable nanoparticle suspensions that could be used for the incapsulation and intravenous administration of biologically active proteins and oligopeptides.
Biodegradable ultra high strength poly(L‐lactide) rods for bone fixation
Authors: Hyon Suong‐Hyu , Jin Fengzhe , Jamshidi Khosrow , Tsutsumi Sadami , Kanamoto Tetsuo
Published: August 2003

The hydrostatic molecular orientation technique was used to explore the highest mechanical improvements achievable for poly‐L‐lactide (PLLA). The mechanical attributes of these materials designed for bone fracture fixation devices, i.e. bending strength and modulus were measured and compared with those prepared by stretching method. The starting samples were prepared by conventional melt extrusion at 200 °C followed by hydrostatic extrusion at 140 °C using glycerin filled extruder. Uniaxially stretched rods were prepared by drawing in silicon oil at 120 °C. The physical properties of these rods are inadequate as mechanical supports in the dynamic healing process of the bone. Moreover, they underwent a marked strength deterioration when immersed in aqueous buffered solution for 90 days. On the other hand, the hydrostatic extrusion technique produced rods with progressively higher bending strength that showed only a small drop after 90 days hydrolytic degradation. Micrographs suggested a superior molecular orientation and packing, which could be associated with the improved performance. The hydrostatic extrusion technique proved to be a safe and effective approach for strengthening biodegradable polymeric materials for dynamic mechanical support in orthopedic medical devices.
Biodegradation of packaging materials: composting of polyolefins
Authors: Pandey Jitendra K. , Kumar A. Pratheep , Singh R.P.
Published: August 2003

The compostability of LDPE, PP and heterophasic E‐P Copolymers was studied for 5 months under normal and accelerated composting environments. Bio‐susceptibility of pre‐UV (290 nm) treated films (∼ 100μm, 5 X 5 cm) was measured by monitoring the weight loss, intrinsic viscosity [η], chain scission, functional group evolution (FT‐IR) and surface morphology (SEM). It was found that with the increasing time of UV treatment, weight loss was increased in compost. Almost linear decrease in [η] was observed for irradiated and composted samples. The temperature of compost and extra addition of thermophilic microbes significantly influenced the biodegradation. In general, it was concluded that the composition of copolymer markedly affected the compostability and increased ethylene content, slowed down the microbial activity.
The enzymatic degradation of commercial biodegradable polymers by some lipases and chemical degradation of them
Authors: Tsutsumi Chikara , Hayase Nobuki , Nakagawa Katsuhiko , Tanaka Suminori , Miyahara Yasushi
Published: August 2003

Biodegradable polyesters, poly(butylene succinate adipate) (PBSA), poly(butylene succinate) (PBS), poly(ethylene succinate) (PES), poly(butylene succinate)/poly(caprolactone) blend (HB02B) and poly(butylene adipate terephthalate) (PBAT), were evaluated about degradability for enzymatic degradation by lipases and chemical degradation in sodium hydroxide solution. In enzymatic degradation, PBSA was the most degradable by lipase PS, on the other hand, PBAT containing aromatic ring was little degraded by eleven kinds of lipases. In 1N NaOH solution, degradation rate of PES with ethylene unit was extremely fast, in comparison with other polyesters. Interestingly the degradation rate of PBSA in enzymatic degradation by lipase PS was faster than in chemical degradation.
Additives for controlled degradation of agricultural plastics: ENVIROCARETM
Authors: Bonora M. , De Corte D.
Published: August 2003

ENVIROCARETM additives are specialty chemicals that can be added to conventional thermoplastic polymers to obtain degradable agricultural plastic articles. Their main benefits are connected with their possible incorporation in “commodity plastics”. This allows the production of degradable agriculture plastic articles processable with standard manufacturing machines, without negative effects on the main properties of the plastic article and with evident costs advantages. Furthermore, required outdoor exposure lifetimes for different articles and different environmental conditions can be modulated with the incorporation of the appropriate additive loading in the plastic and with combinations of selected stabilizers. Mulch films, small tunnel films, banana bags and sleeves, direct covers, non‐woven, ropes, twines and pots are convenient agricultural applications for this technology. ENVIROCARETM products induce plastic degradation following a two steps mechanism: first the plastic is photo‐ and thermo‐oxidized during the outdoor exposure; once the degradation process has been activated by light or heat, ENVIROCARETM acts by increasing the degradation rate and degradation continues until the article is totally degraded. Since degradation is both photolytically and thermally triggered, degradation occurs both at the surface and in the soil. Experimental laboratory results allow the assessment of the contribution of different important parameters ‐ i.e. type of polymer, type of article, presence of other stabilizers/additives or pigments, different environmental conditions‐ on the control of the article lifetime and degradation. Field exposure in different environments integrates the test results and allows for the design of the additive systems adapted to the specific needs.
Effect of the remaining lanthanide catalysts on the hydrolytic and enzymatic degradation of poly‐(ϵ‐caprolactone)
Authors: Gattin Richard , Cretu Adina , Barbier‐Baudry Denise
Published: August 2003

Poly‐(ϵ‐caprolactone) is a biodegradable polymer, which can be used for both medical and environmental applications.

Due to its multiple applications the synthesis of such a polymer has been attracting an increasing attention in the past few decades.

In our work, the polymers were synthesised by bulk polymerisation, using different lanthanide halides as initiators. The lanthanide derivatives are known as very active catalysts in the ring‐opening polymerisation of cyclic esters. Moreover, they are not toxic in comparison of catalysts, which are usually used for this synthesis.

In this paper, the influence of the lanthanides on both the hydrolytic and enzymatic degradation of the PCL obtained by ring‐opening polymerization of ϵ‐caprolactone with different lanthanide‐based catalysts such as: lanthane chloride (LaCl3), ytterbium chloride (YbCl3) and samarium chloride (SmCl3) was assessed.

Samarium seems to slightly accelerate the hydrolytic degradation of the polymer and to slow down or inhibit its enzymatic degradation, mainly when the molecular weight of the polymer is high. The behaviour of PCL containing another lanthanide like lanthane is dependent on the nature of the metallic ion. Complete degradation, by the Lipase PS from Pseudomonas cepacia, is achieved only with Ytterbium.
Thermal and mechanical behavior of amorphous and semi‐crystalline poly(vinylidene fluoride)/poly(methyl methacrylate) blends
Authors: Jarray Jlidi , Larbi Fadhel Ben Cheikh , Vanhulle Faustine , Dubault André , Halary Jean Louis
Published: August 2003

Various PVDF/PMMA (poly(vinylidene fluoride)/poly(methyl methacrylate)) blends were selected for mechanical testing in compression. At low PVDF content (less than 50/50 w/w), the blends remain amorphous and PVDF and PMMA are fully miscible. In PVDF‐richer blends, PVDF crystallizes in part, leading to a PMMA‐enriched homogeneous amorphous phase. In this study, the degree of crystallinity was set at equilibrium by appropriate annealing of the samples before testing. Mechanical analysis was focused on the low deformation range, and especially on the yield region. Depending on the test temperature and blend composition, three types of response were identified, depending on whether plastic deformation is influenced: 1) by the PMMA secondary relaxation motions, 2) by the PVDF/PMMA glass transition motions, or 3) by the crystallite‐constrained PVDF chains.
Morphology and micromechanical behaviour of styrene/butadiene block copolymers and their blends with polystyrene
Authors: Adhikari Rameshwar , Michler Goerg H. , Knoll Konrad
Published: August 2003

The correlation between the morphology and the deformation mechanism in styrene/butadiene block copolymers having modified architecture and in blends with homopolymer polystyrene (hPS) was studied. It was demonstrated that the morphology formation in the block copolymers is highly coupled with their molecular architecture. In particular, the micromechanical behaviour of a star block copolymer and its blends with polystyrene was investigated by using electron microscopy and tensile testing. A homogeneous plastic flow of polystyrene lamellae (thin layer yielding) was observed if the lamella thickness was in the range of 20 nm. The deformation micromechanism switched to the formation of craze‐like deformation zones when the average PS lamella thickness changed to about 30 nm and more.
Interfacial chemistry and morphology of in‐situ compatibilised PA‐6 and PBT based blends
Authors: van Duin Martin , van Gurp Marnix , Leemans Luc , Walet Monique , Aussems Marcel , Martin Philippe , Legras Roger , Machado Ana V. , Covas Jose A.
Published: August 2003

Reactive blending is the preferred route for obtaining rubber‐toughened engineering plastics. In this study the chemistry and morphology of in‐situ compatibilised PA‐6/EPM‐g‐MA blends and PBT/E‐MA‐GMA blends are compared. Despite the different chemical structures formed (PA‐6: cyclic imide; PBT: ester), the different side‐reactions that take place (PA‐6: chain scission; PBT: rubber crosslinking) and the different reaction rates (PA‐6: very fast; PBT: rather slow), a general description of reactive blending is proposed. First, a very fast physics‐controlled dispersion of the rubber phase into the polycondensate matrix occurs (from milimeter to micrometer scale). Then the interface, thus generated, is covered via graft‐copolymer formation. This results in a stabilisation against coalescence and in a reduction of the interfacial tension, enabling further dispersion of the rubber phase. In the case of PA‐6/EPM‐g‐MA blends the graft formation occurs so quickly that when the physics‐controlled dispersion is completed, the final dispersion is achieved. In the case of PBT/E‐MA‐GMA blends the graft formation is much slower and the chemistry‐controlled dispersion can hence be considered as a secondary process, yielding the final morphology.
Functionalization of polyolefins by reactive processing: influence of starting reagents on content and type of grafted groups
Authors: Passaglia Elisa , Coiai Serena , Aglietto Mauro , Ruggeri Giacomo , Rubertà Marco , Ciardelli Francesco
Published: August 2003

Previous studies carried out in our laboratory on the functionalization of ethylene polymers (homo and copolymers) through free radical processes, using mechanical mixers and/or extruders with diethylmaleate (DEM) and dicumyl peroxide (DCP), have shown that the presence of branched α‐olefin blocks favours degradation versus functionalization and crosslinking whereas these last are more effective with linear ethylene blocks.

In this contest the present paper reports about attempts to extend the same processes to propylene polymers by benefitting of the indications of previous results. In particular the one step functionalization of EPM with two or more different groups was carried through the use of different monomers. Moreover the procedure was extended to polypropylene thus obtaining a significant functionalization degree flanked by a remarkable decrease of molecular weight.
Morphology and mechanical properties of extruded ribbons of LDPE/PA6 blends compatibilized with an ethylene‐acrylic acid copolymer
Authors: La Mantia Francesco Paolo , Scaffaro Roberto , Valenza Antonino , Marchetti Augusto , Filippi Sara
Published: August 2003

Two grades of low density polyethylene (LDPE) were blended with polyamide‐6 (PA) in the 75/25 and 25/75 wt/wt ratios and shaped into ribbons with a Brabender single screw extruder. An ethylene‐acrylic acid copolymer (EAA) was used in the 2 phr concentration as a compatibilizer precursor (CP). The morphology of the ribbons and its evolution during high temperature annealing were investigated by scanning electron microscopy (SEM). The results confirmed that EAA does actually behave as a reactive compatibilizer for the LDPE/PA blends. In fact, in the presence of EAA, the interfacial adhesion is improved, the dispersion of the minor phase particles is enhanced and their tendency toward fibrillation is increased, especially for the blends with the higher molar mass LDPE grade. The mechanical properties of the latter blends were found to be considerably enhanced by the addition of EAA, whereas the improvement was relatively modest for the blends with the lower molar mass LDPE. The fracture properties of double end notched samples of the ribbons prepared with the blends containing the lower molar mass LDPE grade were also studied. It was shown that, despite of the increased interfacial adhesion caused by the presence of EAA, the latter plays a measurable positive effect on the fracture properties only for the blends with LDPE as the matrix.
Dependence of the interfacial reaction and morphology development on the functionality of the reactive precursors in reactive blending
Authors: Yin Z. , Koulic C. , Pagnoulle C. , Jérôme R.
Published: August 2003

PMMA containing 50 wt% of anthracene‐labeled PMMA chains end‐capped by a phthalic anhydride group (anth‐PMMA‐anh) has been melt blended at 180°C with PS containing 33 wt% of chains end‐capped by an aliphatic primary amine (PS‐NH2) and PS bearing 3.5 pendant amine groups (as an average) along the chains (PS‐co‐PSNH2), respectively. The reactive chains have been synthesized by atom transfer radical polymerization. Conversion of anth‐PMMA‐anh into PS‐b‐PMMA and PS‐g‐PMMA copolymers has been monitored by SEC with a UV detector. The interfacial reaction mainly occurs in the initial melting and softening stage (<1.0 min.), although at a rate which strongly depends on the number of reactive groups attached to PS chains, the higher conversion being observed for the PS‐co‐PSNH2 containing blends. The phase morphology depends on the architecture of the in‐situ formed copolymer. Indeed, a coarser phase dispersion is observed in case of the graft copolymer compared to the diblock.
Phase separation by continuous quenching: similarities between cooling experiments in polymer blends and reaction‐induced phase separation in modified thermosets
Authors: Alig Ingo , Rüllmann Maximilian , Holst Marco , Xu Jianjun
Published: August 2003

Small angle light scattering (SALS) has been applied to study the phase separation kinetics in a binary polymer mixture of poly(ethyl methyl siloxane) (PEMS) and poly(dimethyl siloxane) (PDMS). The phase separation was induced by cooling an initially homogeneous mixture with well defined cooling rates. The results have been compared to time resolved SALS and microscopy in the course of reaction‐induced phase separation in mixtures of an epoxy resin and polysulfone (PSU).

For the critical PEMS/PDMS mixture with an upper critical point it was found in a continuous quenching experiment that the time evolution of the scattered light intensity I(q,t) scales with the cooling rate. The similarity to the scaling behavior of I(q,t) in isothermal experiments after fast quenches (scaled by the quench depth) is discussed. A secondary phase separation was found and has been explained by the competition between the growth of the two phase structure during cooling and the mutual diffusion without the assumption of gelation or vitrification.

For the epoxy/PSU mixture with 15% PSU, after the appearance of a bicontinuous structure a secondary phase separation was observed. Mixtures with higher PSU‐contents formed epoxy‐rich droplets in the PSU‐rich matrix by nucleation and growth mechanism. The frustration of the structure growth can be explained by approaching vitrification of one or both phases.

The similarity between continuous cooling experiments in blends and the reaction‐induced phase separation have been discussed in the generalized χN vs. composition phase diagram (N: degree of polymerization, χ: Flory‐Huggms interaction parameter).
Reactive compatibilization of epoxy/polyorganosiloxane blends
Authors: Prolongo S.G. , Cabanelas J.C. , Baselga J.
Published: August 2003

A new thermoset material based on DGEBA with polyaminosiloxane curing agents is presented. The system shows reaction‐induced compatibilization which prevents coalescence of polysiloxane and DGEBA rich domains, leading to gradient structured morphologies. The influence of curing temperature and/or chemical nature of the siloxane on the morphology and surface microhardness were examined. When siloxane is pre‐reacted with epoxypropylphenylether (EPPE), a more homogeneous material is obtained. Microhardness profiles on the material are strongly influenced by the extension of the compositional gradients.
A new class of epoxy thermosets
Authors: Girard‐Reydet Emmanuel , Pascault Jean‐Pierre , Bonnet Anthony , Court François , Leibler Ludwik
Published: August 2003

The reinforcing strategies of epoxy thermosets rely on the control of the phase separation between the additive and the growing thermoset. With standard additives, such as reactive liquid rubbers, the length scale of the resulting domains is the micrometer. Here, we present a route that enable a control of the morphology down to the nanometer scale. This strategy is based upon the self‐assembly process of blends of epoxy and SBM triblock copolymers, namely Poly(Styrene‐b‐1,4 Butadiene‐b‐Methyl methacrylate). It relies on the respective affinities between the epoxy precursors and each of the three blocks. Liquid epoxy has a strong affinity for PMMA, whilst it is not miscible with polystyrene nor polybutadiene at standard processing temperatures. Thus, within the reactive system, microphase separation leads to a regular network of S‐B domains. This nanostructure is governed by thermodynamics. The size and geometry of the dispersed domains are controlled by the concentration and the ratio between blocks lengths. The domain size is of the order of magnitude of the chain length, ranging typically from 10 to 30 nanometers. What controls the blend's morphology throughout the curing process of the thermoset was one topic on which we focused our interest. Nanostructured thermosets have been obtained. These supramolecular architectures yield significant toughness improvements while preserving the transparency of the material. The reinforcing mechanisms are not yet fully understood : it is intriguing to induce significant toughening with elastomer domains smaller than 30 nanometers in diameter. Besides being efficient epoxy tougheners, SBM can broaden the scope of applications of thermosets due to specific rheological behaviors. Thanks to the self assembly process taking place in the blend of the SBM block copolymers with the epoxy thermosets precursors, the reactive solvent can be turned into a reactive gel or solid (before curing). This physical gelation is induced by the microphase separation and is thus thermoreversible. At relatively moderate loadings of block copolymers the reactive blend behaves like a thermoplastic material, with adjustable modulus and tackiness. These results evidence that SBM block copolymers open a broad area for designing new class of thermoset materials.
Blends of a new thermoplastic in a thermoset epoxy matrix
Authors: Constantin François , Fenouillot Françoise , Guillaume Jean‐Luc , Koenig Raymond , Pascault Jean‐Pierre
Published: August 2003

Properties of thermoplastic modified epoxy network have been studied. The particularity of this work is the use of new thermoplastic epoxies whose structure is close to the final matrix. Blends of thermoset epoxy (Diglycidyl Ether of Bisphenol A/4‐4′ methylenebis [3‐chloro 2,6‐diethylaniline]) with a thermoplastic content from 5 to 40%w have been realised. Initial miscibility in the thermoset precursors shows an UCST behaviour with a maximal value near 130°C for a thermoplastic content of 10%. Due to the presence of tertiary amine and pendant hydroxyl groups on the thermoplastic backbone, epoxy amine reactions are faster than for the neat system but the thermoplastic seems not to have reacted with the thermoset network. The final blends are transparent but toughening increase is rather low.
Critical DNA damage recognition functions of XPC‐hHR23B and XPA‐RPA in nucleotide excision repair
Authors: Thoma Brian S. , Vasquez Karen M.
Published: August 2003

It has been reported that 80–90% of human cancers may result, in part, from DNA damage. Cell survival depends critically on the stability of our DNA and exquisitely sensitive DNA repair mechanisms have developed as a result. In humans, nucleotide excision repair (NER) protects the DNA against the mutagenic effects of carcinogens and ultraviolet (UV) radiation from sun exposure. By preventing mutations from forming in the DNA, the repair machinery ultimately protects us from developing cancers. DNA damage recognition is the rate‐limiting step in repair, and although many details of NER have been elucidated, the mechanisms by which DNA damage is recognized remain to be fully determined. Two primary protein complexes have been proposed as the damaged DNA recognition factor in NER: xeroderma pigmentosum protein A–replication protein A (XPA‐RPA) and xeroderma pigmentosum protein C‐human homolog of RAD23B (XPC‐hHR23B). Here we compare the evidence that supports damage detection by these protein complexes and propose a model for DNA damage recognition in NER based on the current understanding of the roles these proteins may play in the processing of DNA lesions. © 2003 Wiley‐Liss, Inc.
Biallelic expression of the H19 gene during spontaneous hepatocarcinogenesis in the albumin SV40 T antigen transgenic rat
Authors: Manoharan Herbert , Babcock Karlee , Willi Jonathan , Pitot Henry C.
Published: August 2003

Previous studies in this laboratory have demonstrated that the earliest cytogenetic alteration in the development of hepatic neoplasms in a transgenic strain of rats bearing the albumin Simian virus 40 T antigen (Alb SV40 T Ag) construct was a duplication of the chromosome 1q4.1‐1q4.2 band. In this region, in the rat genome a cluster of linked imprinted genes occurs. One of these imprinted genes, H19, which is expressed in fetal liver but not in adult liver, was found to be expressed in virtually all neoplasms investigated. A single‐nucleotide polymorphic marker in the H19 coding sequence was identified in two rat strains and utilized for the investigation of H19 imprinting. Our results reveal monoallelic expression of the maternal gene in fetal liver, but biallelic expression of the H19 gene in liver neoplasms, thus demonstrating the basis for the deregulation of the imprinted gene expression during hepatocarcinogenesis. These results suggest that the loss of genomic imprinting of the H19 gene found in the liver neoplasms of the Alb SV40 T Ag rat may result not from allelic loss, but from adverse changes in the epigenetic imprints present in the 5′‐upstream region of the H19 promoter of the parental alleles. © 2003 Wiley‐Liss, Inc.
Tunable electromagnetic bandgap performance of coplanar waveguides periodically loaded by ferroelectric varactors
Authors: Kuylenstierna D. , Subramanyam G. , Vorobiev A. , Gevorgian S.
Published: August 2003

To achieve tunable electromagnetic bandgap (EBG) performance, ferroelectric varactors are considered, in LC circuits, for periodically loading coplanar waveguides (CPWs). Asymmetric or symmetric tuning of the bandgap width may be achieved by changing the capacitance of the varactors in the LC circuits. To validate this concept, tunable EBG arrays based on silicon substrate CPWs, including thin film SrTiO3 (STO) varactors, are fabricated and tested experimentally. The EBGs are designed so that the first band gap starts between 20 and 30 GHz. Up to 10% tuning is achieved, under 20‐V DC applied bias, in the EBG structures. © 2003 Wiley Periodicals, Inc. Microwave Opt Technol Lett 39: 81–86, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.11134
Lossy effects on the transient propagation in LTCC coplanar waveguides (CPWs)
Authors: Yin W. Y. , Guo B. , Dong X. T. , Gan Y. B.
Published: August 2003

The effects of dielectric, radiative leakage and ohmic losses in CPWs on the propagation of Gaussian and sinusoidally modulated Gaussian pulses are investigated. These CPWs are assumed to be fabricated on a single‐layer low‐temperature co‐fired ceramic (LTCC) substrate. It is shown that, based on the improved empirical formula for accurate prediction of the ohmic attenuation constant presented by Liao et al., the lossy effects in LTCC CPWs are dominated by the ohmic loss of the center and ground conductive planes in the frequency range up to 40 GHz. © 2003 Wiley Periodicals, Inc. Microwave Opt Technol Lett 39: 94–97, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.11137
A hybrid implicit‐explicit FDTD scheme with weakly conditional stability
Authors: Huang Binke , Wang Gang , Jiang Yansheng , Wang Wenbing
Published: August 2003

A hybrid implicit‐explicit FDTD (HIE‐FDTD) algorithm is proposed in this paper. In the HIE‐FDTD algorithm, semi‐implicit‐ and explicit‐difference schemes are imposed on two different field components, respectively, and the field component with implicit difference is updated by solving simple tridiagonal matrix equations. The HIE‐FDTD method, although conditionally stable, allows for larger time‐step size than the conventional FDTD method because the stability condition of the HIE‐FDTD method is weaker than that of the conventional Yee's FDTD algorithm. The demonstrated numerical dispersion relation of the HIE‐FDTD method is found to be identical to that of the ADI‐FDTD method. The accuracy and efficiency of the HIE‐FDTD are verified by numerical simulation results. © 2003 Wiley Periodicals, Inc. Microwave Opt Technol Lett 39: 97–101, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.11138
Analysis of four‐wave mixing in optical fiber links with non‐uniform chromatic dispersion
Authors: Souza J. R. , Harboe P. B.
Published: August 2003

The four‐wave mixing (FWM) process in single‐mode optical fibers is investigated by considering that a zero‐dispersion wavelength varies along the length of the fiber link, which is represented as a series of segments with different lengths, propagation constants, and zero‐dispersion wavelengths. The results indicate that new optical frequencies are efficiently generated for particular combinations of the input‐signal wavelengths, even when the phase‐matching condition is not fully met. © 2003 Wiley Periodicals, Inc. Microwave Opt Technol Lett 39: 102–105, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.11139
Analysis of the mixing effect in InAlAs/InGaAs metal‐semiconductor‐metal photodetectors
Authors: Aliberti K. , Stann B. , Svensson S. , Mehandru R. , Ren F. , Shen H.
Published: August 2003

The optoelectronic mixing effect in InAlAs Schottky‐enhanced InGaAs‐based metal‐semiconductor‐metal photodetectors (MSM‐PDs) is analyzed. The measured frequency bandwidth of the optoelectronic mixer (OEM) is less than that of a corresponding photodetector. The mixing efficiency depends on the light‐modulation, local‐oscillator, and mixed‐signal frequencies and decreases nonlinearly with a decrease in optical power. We present a circuit model of the OEM to explain the experimental results. © 2003 Wiley Periodicals, Inc. Microwave Opt Technol Lett 39: 108–112, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.11141
Design of broadband and arbitrary profile filters using large chirped fiber grating
Authors: Xia Li , Li Xuhui , Chen Xiangfei , Wang Peng , Xie Shizhong
Published: August 2003

A method is presented for designing and fabricating broadband and arbitrary profile filters using large chirped fiber grating. The relationship between grating reflectivity and chirp coefficient is discussed. By changing the ultraviolet (UV) light exposure dose along the grating, the complex refractive index modulation profile can be obtained. A broadband filter used for sensing with a linear reflectivity profile is produced through this method. © 2003 Wiley Periodicals, Inc. Microwave Opt Technol Lett 39: 115–117, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.11143
Bandwidth enhancement of plastic optical fiber with multi‐step core by thermal diffusion
Authors: Lee Seihyoung , Paek Un‐Chul , Chung Youngjoo
Published: August 2003

We propose a novel method to enhance the bandwidth of plastic optical fiber with a multi‐step core by forming a graded‐index core through thermal diffusion in the performance stage. The numerical simulation results indicate that the bandwidth of the optical fiber can be significantly enhanced by this method. © 2003 Wiley Periodicals, Inc. Microwave Opt Technol Lett 39: 129–131, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.11147
Accurate CAD formulas with physical insight on microstrip‐line couplers by synthetic asymptote
Authors: Tang Wanchun , Chow Y. Leonard
Published: August 2003

This paper obtains simple CAD formulas of a microstrip‐line coupler in even and odd modes by synthetic asymptote. The formulas relate the line structure to the even‐ and odd‐mode impedances and the effective dielectric constants. The formulas are simple and accurate, and they provide good physical insights on the design properties. The average errors are less than 2%. © 2003 Wiley Periodicals, Inc. Microwave Opt Technol Lett 39: 131–135, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.11148
A folded metal‐plate monopole antenna for multiband operation of a PDA phone
Authors: Lin Chia‐Ching , Tung Hao‐Chun , Chen Hong‐Twu , Wong Kin‐Lu
Published: August 2003

A novel monopole antenna, constructed easily by folding a simple metal plate, is presented. The folded metal‐plate monopole antenna shows a compact size of 10 × 10 × 70 mm3 and has three wide impedance bandwidths at about 0.9, 2.0, and 5.0 GHz, thus covering the operating bandwidths of most of the present‐day mobile communication systems (AMPS, GSM, DCS, PCS, and UMTS) and the WLAN systems in the 2.4/5.2/5.8‐GHz bands. With the antenna performance obtained, the proposed antenna is suitable for application in a PDA phone for both mobile communications and WLAN applications. © 2003 Wiley Periodicals, Inc. Microwave Opt Technol Lett 39: 135–138, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.11149
Parabolic dish antenna with offset elliptical multi‐mode feeds for space‐borne remote‐sensing applications
Authors: Sharma S. B. , Singh V. K. , Chakrabarty S. B.
Published: August 2003

This paper presents the design and development of a pencil‐beam scanning parabolic reflector antenna with new multi‐mode elliptical feeds for space‐borne scatterometer application. The feeds have been laterally displaced in the focal plane of the reflector in order to achieve two squinted elliptical beams with the required angular spacing. The asymmetry in the secondary beams has been realized by illuminating the reflector with elliptic sectoral patterns of the elliptical feeds. Sectoral patterns have been synthesized by coupling power into higher‐order modes at the feed aperture. Using this new type of feed, a gain improvement on the order of 0.7 dBi has been achieved, as compared to the reflector antennas illuminated by elliptic feeds of nonsectoral patterns. The computed and measured data on primary and secondary radiation patterns have been presented. The desired gain, beam widths, beam asymmetry, angular spacing between the beams, side‐lobe level, and cross‐polarization level have been achieved. © 2003 Wiley Periodicals, Inc. Microwave Opt Technol Lett 39: 138–141, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.11150
A dual‐band Chebyshev impedance transformer
Authors: Castaldi G. , Fiumara V. , Pinto I. M.
Published: August 2003

This paper presents a simple extension of the Chebyshev quarter‐wave multisection transformer synthesis to dual‐band operation. The method is a variation of the classical Chebyshev transformer design procedure, using a suitable 2nd‐order trigonometric polynomial as the argument of the Chebyshev polynomial. As compared to a single‐band Chebyshev transformer encompassing both required passbands, the proposed design yields significantly better performance. © 2003 Wiley Periodicals, Inc. Microwave Opt Technol Lett 39: 141–145, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.11151
Second‐rank tensors for quasi‐1D periodical electromagnetic structures described by magnetic‐line groups
Authors: Dmitriev V.
Published: August 2003

A method for calculation of the second rank constitutive tensors for symmetrical magnetic quasi‐1D structures in the long‐wavelength approximation is discussed. These structures are, for example, polymers, nanotubes, multilayer films. The method is based on the group theory. Line magnetic groups are used to find the possible forms of the tensors. Examples of the calculated tensors for some groups are presented. © 2003 Wiley Periodicals, Inc. Microwave Opt Technol Lett 39: 152–155, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.11154
Scattering of inhomogeneous cylinders by circuital analysis
Authors: Peñaranda‐Foix Felipe L. , Ferrando‐Bataller Miguel
Published: August 2003

Circuital analysis theory is applied to solve problems of electromagnetic diffraction in nonhomogeneous cylinders. The MAG of a simple element, the circular sector, is calculated as the primary element in the segmentation of greater problems. Circuital theory applied to these problems allows us to resolve problems of greater size and difficulty. © 2003 Wiley Periodicals, Inc. Microwave Opt Technol Lett 39: 155–159, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.11155
Accurate computer‐aided modeling of multilayer GaAs microstrip lines using a spectral‐domain method
Authors: Thakur Jay Prakash , Kedar Ashutosh , Gupta K. K. , Pandey A. K. , Vyas H. P.
Published: August 2003

Multilayer microstrip lines are an integral part of MMIC. This paper presents an analysis of multilayer GaAs microstrip lines using a spectral‐domain method (SDM), taking into account the effect of the variation in the thickness of various layers of substrates on the characteristic impedance and the effective dielectric constant of the line. Some of the theoretical results are validated by the measured results on three‐layer GaAs microstrip lines, showing a close agreement within a 1% deviation over a large frequency range up to 20 GHz. The proposed CAD model is expected to provide an economical and fast CAD procedure for GaAs‐MMIC foundries. © 2003 Wiley Periodicals, Inc. Microwave Opt Technol Lett 39: 159–162, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.11156
Optical code‐division multiplexing systems using common‐zero codes
Authors: Jau Liang‐Lin , Lee Yang‐Han
Published: August 2003

A special architecture using a balance encoder and an on‐off‐keying (OOK) decoder is proposed for an optical code‐division multiplexing system. Different channels can use a common code to encode the zero bits. The constant interference of the system makes the decoder simpler and faster. The performance of the proposed system proves to be superior to that of the pure OOK system. © 2003 Wiley Periodicals, Inc. Microwave Opt Technol Lett 39: 165–167, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.11158