bluuebunny/crossref_metadata_2025 huggingface dataset:
Long-Term Exposure of Adhesively Bonded Thin Polymer Composite Laminates in Low Earth Orbit Environment
Authors: Babayevsky Petr G , Kozlov Nicolai A , Shubin Alexander N , Smirnova Tatiyana N
Published: August 2002

A summary of the results of the long-term passive exposure of adhesively bonded joints of polymer composite laminates on the outboard of the Mir space station and the in situ experiment on the functional cargo block of the International Space Station are presented. Crack resistance, structure and properties of the adhesive joints were examined after passive exposure. Subcritical crack propagation control in the same type of adhesively bonded joints was carried out during the experiment in outer space. It was shown that the long-term exposure increases the brittleness of the adhesive joints due to postcuring processes, elimination of low molecular weight components and interphase damage formation. The subcritical crack propagation velocity is of the same order as on-ground check tests, but can occur under lower GI values.
Production of Volatile CO and CO2 from Oxidized Polyethylene and Graphite Surfaces by Hyperthermal Atom–Surface Collisions
Authors: Zhang Jianming , Minton Timothy K
Published: August 2002

Molecular beam-surface scattering experiments have been used to investigate the mechanisms of the enhancement in material removal rate (identified by the ejection of CO and CO2) when continuously oxidized carbon or hydrocarbon surfaces are bombarded with inert particles (e.g. Ar atoms) possessing kinetic energies in the range 8–22 eV. Collisional enhancement in the material removal rate was observed to increase dramatically above an apparent threshold of ∼8eV. Although the details of the collisional mechanisms must involve complex sputtering processes, the dynamical behaviour of the ejected CO and CO2 may be described in terms of a simple kinematic picture in which an incident fast atom collides with a localized region of the surface that has an effective mass. Collisional, or sputtering, processes such as those identified in this study may be important in the erosion of materials in the low Earth orbital environment, as a result of highly energetic collisions of ambient N2 with oxidized surfaces, and also in ground-based test facilities that subject oxidized surfaces to bombardment by O2 molecules with very high translational energies.
An Improved Interpretation of Recoil Compressive Failure Data for High-Performance Polymers
Authors: Newell J A , Gustafson J M
Published: August 2002

This paper describes an improved methodology for the accurate interpretation of recoil compressive failure data. This new procedure uses a wider portion of the data set in its interpretation than does the method of Allen and is far simpler and less data intensive than the Weibull model proposed by Hayes. Computer simulations using various statistical distributions for the intrinsic recoil compressive strength of a batch of filaments show that this method quickly and accurately converges to an accurate approximation of the mean for the sample set.
Thermal Induced Instability of Thin Polymer Films: A Study by Atomic Force Microscopy
Authors: Gan Daoji , Cao Wenjing , Puat Ng E
Published: August 2002

Systematic studies of thin-film stabilities of random copolymers consisting of decyl methacrylate (DMA)/methyl methacrylate (MMA) units on a polystyrene (PS) layer tethered to silicon wafer have been carried out by atomic force microscopy (AFM) as functions of molecular weight and chemical composition. Upon annealing at an elevated temperature above the glass transition temperature ( Tg), the initially flat polymer films break up into small holes, and finally form macroscopic droplets. The tethered PS layer was found to be dense enough to inhibit penetration of the copolymers into the lower layer during the annealing process. AFM studies at an early stage showed that the velocity of the hole growth was dependent upon both the molecular weights and chemical compositions of the copolymers. However, the equilibrium contact angles of the copolymer droplets formed on the PS layer were more dependent on the chemical compositions than on the molecular weights.
Automated Tow Placed LARC™-PETI-5 Composites
Authors: Hou T H , Belvin H L , Johnston N J
Published: August 2002

LARC™-PETI-5 is a PhenylEthynyl-Terminated Imide resin developed at NASA Langley Research Center (LARC) during the 1990s. It offers a combination of attractive composite and adhesive properties. IM7/LARC™-PETI-5 composites exhibit thermal and thermo-oxidative stability typical of polyimides, superior chemical resistance and processability, excellent mechanical properties, toughness and damage tolerance. It was selected for study in the High Speed Research program aimed at developing technologies for a future supersonic aircraft, the High Speed Civil Transport, with a projected life span of 60 000 h at a cruise speed up to March 2.4. Robust autoclave processing cycles for LARC™-PETI-5 composites have been thoroughly designed and demonstrated, which involved hand lay-up of solvent-ladened ‘wet’ prepregs. However, this type of processing is not only costly but also environmentally unfriendly. Volatile management and shrinkage could become serious problems in the fabrication of large complex airframe structural subcomponents. Robotic tow placement technology utilizing ‘dry’ material forms represents a new fabrication process which overcomes these deficiencies.

This work evaluates and compares mechanical properties of composites fabricated by heated head automated tow placement (dry process) with those obtained by hand lay-up/autoclave fabrication (wet process). Thermal and rheological properties of the robotically as-placed uncured composites were measured. A post-cure cycle was designed due to the requirement of the PETI-5 resin for a 370 °C/1 h hold to reach full cure, conditions which cannot be duplicated during heated head robotic placement. Mechanical properties such as 0° flexural strength and modulus, open hole tensile and compressive strength and moduli, reduced section compression dogbone compressive strength, and modified zippora-medium small (MZ-MS) tensile and compressive properties were obtained on the post-cured panels. These properties compared favourably with those obtained from the wet process.
Imide/Arylene Ether Copolymers-Part II
Authors: Jensen B. J. , Hergenrother P. M. , Bass R. G.
Published: August 2002

A series of novel imide/arylene ether copolymers were prepared from the reaction of an amorphous arylene ether oligomer and a semi-crystalline imide oligomer. These copolymers were thermally characterized and mechanical properties were measured. One block copolymer was end-capped and the molecular weight was controlled to provide a material that displayed good compression moldability and attractive adhesive and composite properties.
Glass-fibre-reinforced Epoxy Composites using Epoxidized Cardanol as Diluent
Authors: Patel M. B. , Patel R. D. , Patel R. G. , Patel V. S.
Published: August 2002

Glass-fibre-reinforced epoxy composites were prepared and evaluatedfor their mechanical chemical and electrical properties. The effect of incorporating epoxidized cardanol as diluent on such properties of the composites based on the diglycidyl ether of bisphenol-A was investigated The tensile strength andflexural strength increased significantly. The composites prepared using epoxy fortifiers showed a good improvement in properties such as tensile strength, flexural strength and interlaminar shear strength.
Physicochemical Studies of PMR Resins. I: Reaction Mechanism and Kinetics at Room Temperature
Authors: Grenier-Loustalot Marie-Florence , Grenier Philippe
Published: August 2002

The reaction mechanism and kinetics of PMR 15 resin (polymerization of monomeric reactants) were studied at low and room temperature using models thoroughly characterized by nuclear magnetic resonance (1H, 13C liquid and solid state) and liquid chromatography. The results indicate a difference in reactvity of the esters at room temperature and competing reactions that lead to large variations in resin pot life structure, with the detection of amide, ester, imine and amine.
Correlation Between Cross-link Density and Dynamic Mechanical Behavior of Castor-oil-based Polyurethane/Poly(Methyl Acrylate) Interpenetrating Polymer Networks-Part XXIV
Authors: Suthar Bhikhu , Patel Nimish
Published: August 2002

A series of two-component polyurethane/poly(methyl acrylate) sequential, interpenetrating polymer networks (IPNs) containing different amounts of polyurethane were prepared. The NCO-to-OH ratio used in the preparation of the first-formed polyurethane network' was varied in order to change the cross-link density in the matrix of these IPNs. The morphology of these IPNs was investigated using electron microscopy, dynamic mechanical analysis and equilibrium compression studies. It was concluded that as the NCO-to-OH ratio increased, the cross-link density increased and thereby the extent of mixing increased.
Alginate Polyelectrolyte Ionotropic Gels-XIX. Spectrophotometric detection of Short-lived Intermediates in Alkaline Permanganate Oxidation of Alginate Polysaccharide
Authors: Makhlouf M. Th. , El-Shatoury S. A. , Hassan R. M.
Published: August 2002

Spectrophotometric evidence for the formation of a short-lived Mn(VI) intermediate has been confirmed during the oxidation of alginae polysaccharide by potassium permanganate in alkaline medium at pH> 12. This Mn(VI) intermediate was characterized by a band at a wavelength of 606 nm, an absorption maximum, with a molar extinction coefficient of 1200 + 50 dm3/mol/cm.
Effect of the Thermal History of the Melt on the Degradation of the Surface Mechanical Properties of Poly(aryl-ether-ether-ketone) as Measured by Microindentation
Authors: Deslandes Yves , Boudreau François
Published: August 2002

In this study, the effect of the thermal history of the melt on the morphology and the mechanical properties of the surface of crystallized poly(aryl-ether-ether-ketone) (PEEK) films was followed by density measurements, X-ray diffraction, differential scanning calorimetry and microindentation. The study has shown a decrease in microhardness of the polymer surface as the temperature at which the polymer is kept in the molten state increases and as the time spent in the molten state becomes longer. The study suggests that keeping PEEK for long periods of time in the molten state, in the presence of oxygen, results in chemical changes (presumably crosslinking involving oxygen atoms) which are responsible for drastic changes in the morphological characteristics of the samples and consequently on the mechanical properties of the surface of the solidified material. Above 400 °C, in air, a total change in surface morphology takes place and the mechanical properties of the surface are degraded. The study also suggests that the negative effects of degradation can be avoided to a large extent if the samples are melted at temperatures below 385 °C for short periods of time and kept from oxygen exposure.
Enhanced Adhesive Performance of Thermoplastic Poly(imide-siloxane) Segmented Copolymer with PEEK®-Graphite Composites by Gas Plasma Treatment
Authors: Yoon Tae-Ho , McGrath James E.
Published: August 2002

The adhesive bond performance of PEEK®-graphite composites (APC-2/AS4) with melt fabricated films derived from either a novel thermoplastic poly(imide-30 wt% siloxane) segmented copolymer or commercial thermoplastic polyetherimide (Ultem® 1000), has been studied as a function of surface modifications. The latter included grit blasting and gas plasma etching treatments with oxygen, ammonia, nitrogen and argon. Adhesive bond strength was evaluated with single lap shear samples (SLSS) which were prepared from PEEKl-graphite composite adherends and compression molded thermoplastic poly(imide-30 wt% siloxane) segmented copolymer film adhesives. Greatly improved single lap shear strength values were obtained by several gas plasma treatments as well as by grit blasting. For example, SLSS values were increased from less than 1000 psi to approximately 5000 psi. The morphological and chemical changes of PEEKS-graphite composites with surface treatment were investigated by scanning electron microscopy (SEM), contact angle measurement and X-ray photoelectron spectroscopy (XPS). The results suggest that the improved adhesive bond strength produced by the gas plasma treatments was a function of the interaction of derived surface acidic functional group(s) with the 'basic' polyimide adhesives.
The effect of impurities on gel times for TGDDM epoxy resins cured with DDS
Authors: St John N A , George G A , Cole-Clarke P A , Mackay M E , Halley P J
Published: August 2002

The impurities present in the commercial (Ciba-Geigy) N,N,N',N'-tetraglycidyl-4,4'-diaminodiphenylmethane (TGDDM) resins MY720 and MY72I and a purified TGDDM resin were studied using high-performance liquid chromatography and infrared spectroscopy. The cure kinetics for the three resins cured with 27% 4,4'-diaminodiphenylsulfone (DDS) were described using a previously developed kinetic model and near-infrared spectroscopy with the catalysis of epoxide reactions by impurity hydroxyl groups being seen to have a large effect on the initial rate of epoxide reaction. The gel times were determined using the crossover point between storage and loss moduli (i.e. tan (= 1) as measured using dynamic rheometry. An impurity effect on the-degree of epoxide reaction necessary for gelation to occur was identified and an empirical relationship was developed to quantify this effect. An approach was proposed for the prediction of gel times for TGDDM resins of any purity cured with DDS combining the use of the kinetic model and empirical gel time function.
Polyetherimides—synthesis and structure-property relationships
Authors: Davies Martin , Hay John N , Woodfine Barry
Published: August 2002

Polyetherimides have been synthesized by two complementary routes starting from 4-halophthalic anhydride. A range of polymers has been prepared by varying the structure of the diamines and bisphenols employed in the syntheses. These polymers have been characterized by their m spectra, molecular weight and thermal properties. The applicability and limitations of the synthetic routes are discussed. Structure-property (glass transition temperature, Tg relationships are elucidated and discused in terms of the structural fragments in the polymer chain. Chain flexibility, rotational freedom and inter-chain interactions are all important parameters affecting the polymer properties. The effect of polymer molecular weight on Tg is also discussed.
A kinetic study and the glass-reinforced composites of a liquid diglycidyl ether of bisphenol-P epoxy resin
Authors: Parekh J K , Patel R G , Patel V S
Published: August 2002

The curing reaction of liquid epoxy resin based on l,l'-bis(4-hydroxyphenyl) cyclopentane with different amines, in the presence or absence of a fortifier, has been studied by differential scanning calorimetry (DSC). The glass-fibre-reinforced composites of liquid diglycidyl ether of bisphenol-P (DGEBP) were prepared using different amines as curing agent with/without fortifier and evaluated for their physical properties (such as density,% resin content and% void content) and mechanical properties (such as flexural strength, interlaminar shear strength and shore-D hardness). The laminates were also evaluated for their chemical resistance and electrical properties. It was found that using an epoxy fortifier (PGEHA) reduces the mechanical properties of the DGEBP-curing agent system.
New functionalized poly(arylene-ether ketone)s and their use as modifiers for bismaleimide resin
Authors: Stenzenberger H D , König P
Published: August 2002

A series of new functionalized poly(arylene-ether ketone) copolymers has been prepared by the nucleophilic aromatic displacement reaction from 4,4'-difluorobenzophenone and mixtures of bisphenol-A and 2,2'-bis(3-allyl,4-hydroxyphenyl)-hexat Luoropropane (6F-DABA) in the presence of potassium carbonate. The propenyl functional groups are statistically distributed along the polymer backbone and their concentration was tailored by adjusting the concentration of the starting monomers. These functionalized poly(aryleneether ketone)s (FPAEK) were used as thermoplastic modifiers for a bismaleimide (BMI) resin. The influence of the propenyl group concentration on the toughness of BMI,'FPAEK blend systems was studied.
Syntheses and blend behavior of poly(phenylene thioether ether ketone)s (PTEKs) and poly(phenylene sulfone ether ketone)s (PSEKs)
Authors: Glatz F P , Mifihaupt R
Published: August 2002

A series of poly(phenylene thioether ketone)s (PTEKs) containing well defined oligo(phenylene sulfide) segments has been prepared via the nucleophilic aromatic substitution of bis(4-fluorobenzoyl)-terminated oligo(phenylene sulfide)s with various bisphenols. Amorphous and partially crystalline PTEKs with glass transition temperatures ranging from 110C to 184 C have been obtained. Poly(phenylene sulfone ether ketone)s (PSEKs), prepared by oxidizing PTEKs in a formic acid/hydrogen peroxide slurry. and PTEKs derived from 4,4'-bis(4-fiuorobenzoyl)diphenylsulfide and hydroquinone are miscible with Ultrason E2010P (PES). The thermal, dynamic mechanical and morphological properties ofPTEK/PES and PSEK/PES blends are reported.
Studies on the Properties of Glass-Reinforced Polyurethane Composites and Thick Films
Authors: Parekh J K , Patel R G
Published: August 2002

Thick films and glass-reinforced composites of the totuene 2,4-diisocyanate-based urethane derivative of the acrylated diglycidylether of bisphenol-A were prepared using various amines such as hexamethylene diamine (HMDA), 4,4'-methylene bis(2-chloroaniline) (MOCA), benzidine (Bz) and diaminodiphenylmethane (DDM) as curing agents. The characterization of these laminates and thick films included mechanical properties, dielectric properties and chemical resistance properties. It was observed that neat resin casts and laminates behaved as very good insulating materials and showed good resistance towards chemicals.
The Effect of Changing Chain Stiffness on Morphology in a Family of Thermotropic Copolyesters
Authors: Stellt David T , Donaldt Athene M , MacDonald William A
Published: August 2002

The behaviour of a family of polymers containing equimolar amounts of hydroquinone and isophthalic acid residues, together with changing proportions of hydroxybenzoic acid moieties has been studied. The response of the polymers to an external shear field has been monitored using a polarizing microscope. The conditions which lead to the formation of the banded texture for each of the polymers has been determined. It is found that compositions which are isotropic at rest can form the banded texture following shear at sufficiently high rates. However, the bands so formed are not stable upon annealing. The optical features of the banded texture, its period and underlying trajectory, are determined both by the polymer composition and the conditions of shear.
The synthesis, characterization and polymerization kinetic study of a series of related addition polyimides
Authors: Barton John M , Hamerton Ian , Rose John B , Wamer David
Published: August 2002

A series of eight addition polymides (aspartimides) was prepared in which the imide and amino groups were attached to the ends of aromatic residues containing two or four phenylene rings. The co-monomers (bis-maleimides. BMIs, and diamines) were purified using column chromatography before being fully characterized by spectroscopic techniques. The thermally induced Michael addition and polymerization reactions of the blended co-monomers were monitored using differential scanning calorimetry (Dsc) at several heating rates to enable the kinetics of the processes to be investigated. The thermal stabilities of the thermoset products of these aspartimides were evaluated by thermogravimetric analysis (TGA). Dynamic mechanical thermal analysis (DMTA) was employed to test the physical properties of the neat resins.
A liquid elastomer for epoxy resin toughening
Authors: Padma A , Rao R M V G K , Subramaniam C
Published: August 2002

A liquid elastomer was synthesized using butyl acrylate, acrylic acid and acrylonitrile. The elastomer was characterized and used as a toughener for a high-functionality novolac epoxy resin to improve the impact strength of the resin castings. A chemical reaction between the epoxy resin used and the liquid elastomer synthesized was confirmed by infrared and dynamic mechanical analysis. Preliminary results indicated a 66% increase in impact strength of the castings with addition of 10% by weight of the elastomer. Scanning electron micrographs of the fractured surfaces showed the phase separation of the elastomer.
Ceric-induced grafting of acrylonitrile onto sodium alginate: kinetics and mechanism and effects of the reaction medium
Authors: Shah S B , Patel C P , Trivedi H C
Published: August 2002

The kinetic scheme of free radical graft copolymerization of acrylonitrile (AN) onto sodium alginate, using ceric ammonium nitrate as an initiator, has been proposed and equations relating the values of Rp, Rr and Rh are also suggested. The results have been found to be in good agreement with the proposed mechanism. The per cent grafting of AN onto sodium alginate has also been determined as a function of composition of the mixed solvents comprising methanol: water, ethanol: water, n-propanol:water and n-butanol: water systems. The reaction medium has been found to play an important role in graft copolymerization. The results of the effect of the reaction medium on grafting are also discussed.
Positive-working photosensitive polyimide precursor based on polyisoimide using nifedipine as a dissolution inhibitor
Authors: Mochizuki Amane , Yamada Kazuo , Teranishi Tadashi , Matsushita Koichi , Ueda Mitsuru
Published: August 2002

A positive-working photosensitive polyimide precursor based on polyisoimide (PFII) and nifedipine (1,4-dihydro-2,6-dimethyl-4-(nitrophenyl)-3,5-pyridinedicarboxylic acid dimethylester) (DHP) as a photosensitive compound has been developed. P11 was prepared by the ring-opening polyaddition of oxydiphthalic anhydride (ODPA) and 3,3' diamino diphenylsulphone (3,3'-DDS), followed by the treatment of trifluoroacetic anhydridetriethylamine in N-methyl-2-pyrrolidone (NMP). PII film showed excellent transparency at 365 nm and 436 nm. The dissolution behaviour of PII film containing 20 wt% of DHP after exposure and post-exposure bake (PEB) has been studied. It was found that the dissolution rate of the exposed area was about six times faster than that of the unexposed area due to the photochemical reaction of DHP in P11 film. The photosensitive polyimide precursor containing 20 wt% of DHP showed a sensitivity of 45 mJ cm- 2 and a contrast of 2.4 with 365 nm light when post-baked at 150C for 10 min and developed with cyclohexanone at 50C.
Effects of catalysts on the model reactions of several maleimide resin systems—(I) Amine-modified maleimide
Authors: Enoki Takashi , Takeda Toshiro , Ishii Keiichiro
Published: August 2002

A detailed investigation on the effects of catalysts on'the curing reactions of maleimide, amine-modified maleimide systems was carried out using model reactions. N-phenylmaleimide (PMI) and N,N'-diphenylaspartimide (API) were selected as model compounds. The degree of polymerization of PMT is controlled by changing catalysts (imidazole catalyst and radical catalyst). The radical catalytic effect is hindered by API. As the polymerization degree of PMI in the model reaction corresponds to the crosslinking density of the maleimide resin system, the choice of catalyst could control the crosslinking density and structure of the maleimide resin system, which could also affect the physical and mechanical properties.
Synthesis of poly(amide-imide)s by palladium-catalysed polycondensation of aromatic dibromides containing imide structure, aromatic diamines and carbon monoxide
Authors: Ueda Mitsuru , Yokoo Takayoshi
Published: August 2002

A general method for the preparation of aromatic poly(amide-imide)s, which involves the palladium-catalysed polycondensation of aromatic dibromides containing imide structural units, aromatic diamines and carbon monoxide, has been developed. Polymerizations were carried out in N,N-dimethylacetamide (DMAc) in the presence of palladium catalyst, triphenylphosphine and 1,8-diazabicycIo[5,4,0]-7-undecene (DBU), and gave a series of poly(amide-imide)s with inherent viscosities up to 0.66 dl g-1 under mild conditions. The polymers were quite soluble in strong acids, dipolar aprotic solvents and pyridine. Thermogravimetry of the polymers showed excellent thermal stability, indicating that 10% weight losses of the polymers were observed in the range above 460C in air. The glass transition temperatures of the polymers ranged from 240 to 262C. These polymers also showed good tensile strengths and moduli.
Thermal stability predictions of polymeric composites: comparison of medium-term weight loss at 250C with a kinetic mapping procedure
Authors: Hodgkin J H , Jackson M B , Morton T C
Published: August 2002

A comparative evaluation was carried out between two different accelerated thermal aging tests for estimating thermo-oxidative stability (Tos) in advanced composite materials as part of an effort to determine if either could be used as a fast but reliable predictive method for assessing new materials. One test (kinetic mapping) was based on data obtained from highly accelerated thermogravimetric analysis (TGAo) techniques commonly used in matrix polymer synthetic work, the other was based on weight loss during medium-term aging at temperatures closer to the use temperature, and well below Ta. No correlation was found between the two sets of results when the measurements were carried out on a number of commercial as well as some new experimental resin and composite samples. Reasons for the discrepancies are advanced.
Synthesis and properties of aromatic polyimides containing oxyalkylene linkages
Authors: Beltz Mark W , Harris Frank W
Published: August 2002

A series of para-catenated aromatic diamines containing oxyalkylene linkages, i.e., i.2-bis(4-aminophenoxy)ethane, bis[2-(4-aminnophenoxy)ethyl]ether, 1,2-bis[24{4-aminio-phenoxy)ethoxyjethane and bis{2-[2A4-aminophenoxy)ethoxy]ethyllether were polymerized with 3,3',4.4'benzophenonetetracarboxylic dianhydride (BTDA) and pyromellitic dianhydride. The poly(amic acid)s obtained were imidized by both chemical and thermal methods. It was postulated that the incorporation of the flexible linkages in the polyimides' backbones would result in solubility in organic solvents and moderate glass transition temperatures (Tg) that would allow the polymers to be melt processed. However, the polyimides were insoluble and highly crystalline with melting points (Tm) above 400"C. In an attempt to disrupt the polymers' symmetry. mixtures of the diamines and 1,3-bis(3-aminophenoxy)benzene were polymerized with BTDA. The resulting copolymers were insoluble and semrnicrystalline with Tm values near 310C. A polyimide with similar properties was obtained by polymerizing a disubstituted diamine, 2,2-diethyl-t,3-bis(4-aminophenoxy)propane, with BTDA. A soluble polymer that could be melt processed was prepared from BTDA and a meta-catenated diamine containing an oxyalkylene linkage, bis[2-(3-aminophenoxy)ethyl)ether. The polymer had a strong Tg near 156 'C and a weak Tm near 240C.
Side chain liquid crystalline polymers containing siloxane spacer: 7. Syntheses and properties of polyimides and polyamides containing a mesogenic side chain connected with a disiloxane linkage
Authors: Nagase Yu , Takamura Yuriko , Akiyama Eiichi
Published: August 2002

Preparations of polyimides and polyamides containing a mesogenic group in the side chain connected with a siloxane bond in the spacer component were carried out. A 3,5-diaminobenzyloxy-type monomer having a mesogen consisting of a p'-substituted biphenyl benzoate group was prepared by means of hydrosilylation of 1-[3-43,5-dinitrobenzyloxy)propyl]-1,1,3,3-tetramethyldisiloxane with a mesogenic allyloxy compound, followed by catalytic reduction of the two nitro groups. The polyimides were synthesized by polycondensation of the diamine monomers with 4,4'-(hexafluoroisopropylidene)diphthalic anhydride (6FDA), followed by chemical imidization. The polyamides were also synthesized by polycondensation of the diamine monomers with dicarboxylic dichloride compounds, i.e., terephthaloyl dichloride, oxalyl dichloride, malonyl dichlonride, succinyl dichloride, glutaryI dichloride, adipoyl dichloride, pimeloyI dichloride and azelaoyl dichloride. The structural effects on the thermal properties of the polymers were investigated. The obtained polyamides having an aliphatic group in the main chain exhibited an enantiotropic smectic mesophase at around 100-150C, while no mesophase was observed for the polyimides and a polyamide having an aromatic backbone.
Toughening of Epoxy Resins by Polyimides Synthesized from Bisanilines
Authors: Hay J N , Woodfine B , Davies M
Published: August 2002

A range of thermoplastic polyimides has been synthesized and used to modify a DGEBA-DDS epoxy thermoset. The influence of polyimide end-group functionality and particle size has been examined. Increases in fracture toughness of up to three times that of the neat resin have been achieved, together with no loss of modulus. Thermal capability is little affected across the range of modifying polyimides. The influence of copoly(imide–imide)s has also been studied. Morphological examination has revealed a range of structures in the blends, including some which are unusual. A particulate toughening mechanism is proposed for one high fracture toughness system.
Compatibilized Polypropylene Hybrid Composites: Influence of Elastomeric Interlayers on Mechanical Properties and Nucleation Behaviour
Authors: Stricker Florian , Mülhaupt Rolf
Published: August 2002

Two families of polypropylene hybrid composites were prepared by simultaneously compounding polypropylene at 240°C together with SEBS thermoplastic elastomers and filler particles, for example, anisotropic talc and isotropic glass beads. Addition of SEBS was compared with that of maleic-anhydride-grafted SEBS (SEBS-g-MA) to study the role of SEBS compatibility with fillers, especially formation of elastomeric interlayers, on mechanical properties, morphology and nucleation behaviour. At a constant filler volume fraction of 10 vol.%, SEBS and SEBS-g-MA addition were varied between 0 and 20 vol.%. Due to coupling of amino groups at the glass-bead surface with succinic anhydride side chains of SEBS-g-MA, filler particles were encapsulated in a SEBS shell. The improved interfacial adhesion of SEBS-g-MA with respect to SEBS was reflected by higher yield stresses of the compatibilized hybrid composites. Such interlayers were detected by means of transmission electron microscopic imaging of thin sections of talc-based hybrid composites. Investigation of crystallization by means of polarized light microscopy revealed that elastomeric interlayer formation via in situ filler encapsulation markedly reduced filler-induced nucleation of polypropylene crystallization.
Novel Terpolymers: Poly(keto–amine–urea)S
Authors: Patel Hasmukh S , Lad Manhar J
Published: August 2002

Thermally stable polymers containing keto–amine–urea groups have been prepared by condensation of keto–amino groups containing diamine and various diisocyanates. The resulting polymer samples have been characterized by elemental analysis and IR spectra, and Mn estimated by non-aqueous conductometric titration and thermogravimetry. Curing of commercial epoxy resin-DGEBA by employing these polymers was scanned on a differential scanning colorimeter (DSC). Glass fibre reinforced composites (i.e. laminates) based on such terpolymer–epoxy resin system have also been prepared and characterized.
Curing of Epoxy Resin with Styrene–Maleic Anhydride Copolymer: A Differential Scanning Calorimetric Investigation
Authors: Vora R A , Trivedi H C , Patel C P , Guthrie J T , Kazlauciunas Algy , Trivedik M C
Published: August 2002

Curing reactions of epoxy resin (EP-450) with stryene–maleic anhydride copolymer (St–MAn) samples are investigated by differential scanning calorimetry at a scan rate of 10 °C min−1 in an N2 atmosphere. The overall kinetic parameters of the curing reactions are estimated using Barrett as well as Freeman–Carroll methods based on a single dynamic scan. The curing reactions are found to follow overall first-order kinetics up to about 60–70% completion. Thermogravimetric analysis (TGA) of all the cured samples of epoxy resin (EP-450) with St–MAn copolymer samples has also been carried out at a heating rate of 10 °C min−1 in air.
Synthesis and Characterization of New Fluorinated Poly(Imide Benzoxazole)S
Authors: Mercer Frank W , McKenzie Martin T , Bruma Maria , Schulz Burkhard
Published: August 2002

We have prepared a series of fluorinated aromatic poly(ether imide benzoxazole)s (PEIBs) and fluorinated aromatic poly(imide benzoxazole)s (PIBs). New PEIBs were prepared by polycondensation of aromatic diamines containing both benzoxazole and hexafluoroisopropylidene groups. New PIBs were prepared by polycondensation of bis( o-aminophenol)s, such as 3,3′-dihydroxybenzidine or 2,2-bis(3-amino-4-hydroxyphenyl)hexafluoropropane, with diacid chlorides containing both imide and hexafluoroisopropylidene groups. We have characterized the solubility, film forming ability, thermal stability and dielectric constant of these fluorinated poly(imide benzoxazole)s.
Processing and Properties of IM7/LARC ™ -RP46 Polyimide Composites
Authors: Hou T H , Wilkinson S P , Johnston N J , Pater R H , Schneiderk T L
Published: August 2002

LARC™-RP46 resin system is a PMR type polyimide and is prepared by replacing methylenedianiline in the PMR-15 composition with 3,4′-oxydianiline. This resin system retains the same processing characteristics as PMR-15 but also offers enhanced fracture toughness. Rheological measurements were conducted on pre-imidized LARC™-RP46 moulding powder subjected to various ramp and hold temperature schemes. Adequate flow properties were found with theoretical (formulated) molecular weight 6 ≤1500 g mol−1. Critical transition temperatures for optimizing the process cycle were identified. They included the resin softening point, the imidization reaction peak, the isomerization reaction peak and the gelation point. Utilizing this information, 1.72 × 10 6 Pa (250 psi) cure cycles were designed for B-staged (dry) and unstaged (wet) prepregs. Composite laminates were fabricated which exhibited excellent consolidation and a void content below 0.1–0.2% as measured by image analysis.

IM7/LARC™-RP46 exhibited higher composite mechanical properties than IM7/PMR-15. Short-beam shear strength, flexural strength and flexural modulus were measured at room temperature, 93, 150 and 177 °C. Composite engineering properties were also obtained including longitudinal tension, logitudinal compression, interlaminar shear, short block compression, open hole compression (OHC) and compression strength after impact (CAI). Excellent longitudinal tensile and compressive strengths were obtained and the CAI strength was 40% higher than that for PMR-15. Over 80% retention of all RT strengths were noted at 177 °C.
Study of Thermal Aging of Nadimide Polymer: Physicochemical Characterization of the Properties of the Crosslinked IP960 System
Authors: Habas J P , Peyrelasse J , Grenier-Loustalot M F
Published: August 2002

In order to evaluate the thermostability of the IP960 polymer, we have characterized the physicochemical properties of samples exposed at 295 °C for periods up to 3000 h. According to the time of thermal treatment, various phenomena occur such as an increase in glass transition temperature and crosslink density. After a minimal period of 200 h at 295 °C, the weight loss of samples is representative of the degradation of crosslinked IP950. Using FTIR, we have analysed the changes in the chemical structure of the polymer. We propose a mechanism which could explain the degradation of the crosslinked compound.
New Polymer Syntheses 87. Thermosetting Nematic or Cholesteric Diesters Having Propargyl Endgroups
Authors: Kricheldorf Hans R , Gerken Andreas
Published: August 2002

4-Propargyloxy benzoic acid, 6-propargyloxy-2-naphthoic acid and 4′-propargyloxybiphenyl-4-carboxylic acid were synthesized from the corresponding hydroxy acids and converted into the acid chlorides. Diesters were then prepared by the reaction of these acid chlorides with diphenols such as hydroquinone, methylhydroquinone n-octylthiohydroquinone and phenylhydroquinone. Most of these diesters form an enantiotropic nematic melt but some diesters form a monotropic liquid crystal phase. Cholesteric phases were observed for diesters of ( S)-2-methylbutylthiohydroquinone. Diesters derived from 6-propargyloxy-2-naphthoic acid begin to crosslink above 200 °C with an optimum cure temperature of 240–250 °C. The crosslinking of the 4′-propargyloxybiphenyl-4-carboxylic acid derivatives occurs at a temperature 60 °C higher. Several diesters crosslink in the nematic state, but most of them undergo isotropization before completion of the crosslinking process. Numerous cholesteric blends of nematic diesters and chiral diesters of isosorbide were studied and Grandjean textures with bright colours were found. Thermal crosslinking in the cholesteric phase was feasible in several cases.
Synthesis of a Novel C60-Containing Polyimide: A New ‘Charm-Bracelet’ Type of Polyimide and Copolyimide
Authors: Seo Youngsoo , Jikei Mitsutoshi , Kakimoto Masa-Aki , Imai Yoshio
Published: August 2002

The fullerene-containing polyimides were synthesized by the reaction of diamines and C60-containing dianhydride 2 and copolyimides were synthesized by the reaction of 2, 4, 4′-(hexafluoroisopropylidene)diphthalic anhydride (6FDA) and 4, 4′-diaminodiphenyl ether (ODA). Polyamic acids 3a, b and copolyamic acids 8b–e were soluble in polar aprotic solvents such as DMAc, DMF, DMSO and NMP, whereas 8b–e showed additional solubility in THF. The molecular weights of polyamic acids 3a, b and copolyimides 9b−e determined by gel permeation chromatography were in the range of 1.0 × 10 4−7.8 × 103 and 5 × 104−2.8 × 104 mol g−1, respectively. Polyamic acid 3a ;b contained other lower molecular weight oligomers. TGA results for polyimides and copolyimides showed thermal stability and the 10% weight loss temperatures were in the range of 430–520 °. Distinct glass transition temperatures of C 6′-containing polyimides were not observed by DSC measurement. The cyclic voltammograms of 2 and 3a indicated four reduction waves corresponding to C60 redox reactions, but the polyamic acid 8e showed one reduction wave at −1.39 V.
A Tritium–Hydrogen Exchange Procedure for Determining the Concentration of Exchangeable Sites on PAN Based Carbon Fibres
Authors: Hamerton Ian , Hay John N , Howlin Brendan J , Jones John R , Lu Shui-Yu , Webb Graham A , Bader Michael G
Published: August 2002

A non-destructive tritium–hydrogen exchange procedure has been developed in order to determine the concentration of exchangeable hydrogens on surfaces, and in this particular instance it has been used on carbon fibres. The results show that the concentrations of ‘active sites’ on the surfaces of Courtaulds Grafil XAS and XAU carbon fibres are 2.61 and 0.08 μmol g−1 respectively. When the XAS fibres are subjected to a standard methylation procedure the concentration of exchangeable hydrogens is reduced to 0.79 μmol g−1.On the other hand, when XAU fibres are subjected to oxidation in concentrated nitric acid, the concentration of exchangeable hydrogens is increased to 10.27 μmol g−1.
Synthesis and Properties of a Novel Thermostable Polymer: Fluorinated Polycarbodiimide
Authors: Mochizukiy Amane , Sakamotoy Michie , Yoshiokay Masahiro , Hottay Yuji , Fukuokay Takahiro , Ueda Mitsuru
Published: August 2002

A new fluorinated linear polycarbodiimide (F-PCD) was synthesized by solution polycondensation of a new fluorinated diisocyanate monomer, 4″, 4″′-(hexafluoroisopropylidene) bis(4-phenoxyphenyl isocyanate) (HPI) in the presence of 3-methyl-1-phenyl-2-phospholene-1-oxide (PMO). HPI was prepared from 4″, 4″′-(hexafluoroisopropylidene)bis(4-phenoxyaniline) (HPA) by three steps. The reaction of HPA with phenyl chloroformate gave the corresponding carbamate, which upon reaction with trimethylsilylchloride (TMS-Cl)-triethylamine (TEA), followed by thermal decomposition, provided HPI. The polymer having a number average molecular weight up to 8400 was obtained in quantitative yield. Thermal properties were investigated and we found that the polymer has a higher glass transition temperature ( Tg)upto 230 °C, and a lower dielectric constant at 2.98 at 1 MHz than the conventional polycarbodiimides (PCDs). The linear F-PCD was soluble in a wide range of common organic solvents such as toluene and dichloromethane.
Extrusion Freeform Fabrication of Chopped-Fibre Reinforced Composites
Authors: Calvert Paul , Lin Tung Liang , Martin Hogan
Published: August 2002

Extrusion freeform fabrication is a process whereby three-dimensional parts are built by writing successive layers of material onto a support. In this case, two types of epoxy resin have been formed into test bars containing varying fractions of chopped carbon fibre of various lengths. It is shown that the fibre orientation follows the writing direction and has a large influence on the directional elastic properties of the composite. Test bars have also been formed containing multiple layers of reinforced and unreinforced resin to demonstrate the flexibility of this method.
Communication
Authors: Patel K B , Desai K R , Patelk H S
Published: August 2002

Four various poly(urethane-urea)s (PUUs) were prepared by polycondensation of 3-aminophenol with various diisocyanates. The resultant poly(urethane-urea)s were characterized by elemental analyses, IR spectral studies, number average molecular weight ( Mn) estimated by non-aqueous conductometric titration and thermogravimetry. The electrical properties of these polymers have also been measured at room temperature.
Industrial life insurance, public health campaigns, and public communication of science, 1908-1951
Authors: Lewenstein Bruce V.
Published: August 2002

During the first half of the twentieth century, private life insurance companies in the United States provided an important locus for the public communication of science, through their support of public health campaigns. This paper provides a history of how and why three companies (the Metropolitan, the Prudential, and the John Hancock life insurance companies) drew on their strength in `industrial' life insurance (sold to the lower classes at low, weekly rates) to engage in public health reforms. Only the Metropolitan and the Hancock, however, became active in public communication of health information. The paper suggests that four key factors provided the context for the companies' activities: (1) legislative and social pressure for reform; (2) increases in profits associated with healthier (and therefore longer-lived) customers; (3) ideals of social reform held by individuals in positions of bureaucratic power within the insurance organizations; and (4) organized machinery for weekly contact with and distribution of information to policyholders as a result of the nature of industrial life insurance.
Common sense, science and social representations
Authors: Farr Robert M.
Published: August 2002

The theory of social representations is perfectly suited to the empirical investigation of the public's understanding of science. A sharp distinction is drawn between a scientific theory and its social representation corresponding, respectively, to the contrasting worlds of science and of common sense. Representations of science are to be found in the media as well as in people's minds and need to be sampled and studied in both locations. Moscovici initiated this French tradition of research with his study, in the late 1950s, of psychoanalysis. It is a sociological form of social psychology with close affinities to the sociology of knowledge. The applicability to the natural sciences of a theory developed in relation to the social and human sciences is discussed. The views of Moscovici and of Wolpert are compared and contrasted, especially in regard to the relations between science and common sense. It is argued that the study of social representations is a form of social science that natural scientists need to take seriously if their advice to governments is to become more effective. This is discussed in relation to such health issues as the purity of water and the conduct of government-sponsored campaigns to contain the spread of HIV/AIDS as well as in regard to the wider issues of threats to the ecosystem.
Socially distributed knowledge: five spaces for science to meet the public
Authors: Nowotny Helga
Published: August 2002

By definition, science meets the public in a space which is public. This paper rests upon the assumption that this space has been considerably extended, and continues to differentiate. Imparting scientific knowledge is highly dynamic, and has led to a process of socially distributed knowledge through which an increasing number of heterogeneous sites in society are being created where knowledge is produced. Five public spaces are presented, ranging from the space of individual scientific creativity drawing upon cultural representations available in society, to a space in which ethno-scientific knowledge and practices encounter scientific ones, followed by the space in which the process of professionalization of expert knowledge and standards interlinks with protoprofessional knowledge and standards. The last two public spaces of encounter, the market and the hybrid space of public forums, are perhaps the most familiar. While the concrete patterns of interaction take very different forms, ranging from cooperative or reinforcing to confrontational, it is claimed that the boundaries separating the public from science are becoming more fluid. As a result, not only the public's knowledge of science, but also scientific and technological knowledge, are transformed through these structures.
The public as a communication system
Authors: Neidhardt Friedhelm
Published: August 2002

The public can be considered as a communication field with three main actors: speakers, communicators, and the audience. The characteristics of these actors and the features of their interaction constitute the social infrastructure of public knowledge production. There is both theoretical reason and practical evidence to suggest that the mass media tend to construct science stories in terms of spectacular events, simple causes and unambiguous moral positions. These tendencies create some elementary problems where `science meets the public'. By `popularization' the distance between the communication systems of science and of the public can be reduced but not eliminated.