bluuebunny/crossref_metadata_2025 huggingface dataset:
Environmental change and peatland forest dynamics in the Lake Sentarum area, West Kalimantan, Indonesia
Authors: Anshari Gusti , Peter Kershaw A. , Van Der Kaars Sander , Jacobsen Geraldine
Published: September 2004

Four short pollen and charcoal records from sites within and around Lake Pemerak on the margins of the Danau (Lake) Sentarum National Park in inland West Kalimantan, supported by modern surface samples from the Reserve, provide a partial picture of lowland equatorial vegetation and environments over at least the last 40 000 years. They demonstrate general stability in the distribution of wetland and ombrotrophic (or raised) peatlands through the recorded period with dominance throughout of peatland and swamp forest. However, there was marked variation in sediment accumulation rates and in the floristic composition of the vegetation. The period prior to the last glacial maximum appears to have been the time of most active peatland growth and contrasts with the perception, from previous studies on largely coastal and subcoastal peatlands in Indonesia, that the Holocene was the time of major tropical peat accumulation. A general increase in charcoal, just prior to about 30 000 years ago, suggests that burning became more frequent, and is attributed to initial human impact rather than climate change. The subsequent latest Pleistocene period, embracing the Last Glacial Maximum, is marked by a peak in montane–submontane rainforest taxa, strongly indicating a substantial lowering of temperature. It appears that much of the Holocene is not recorded but recommencement of peat accumulation is evident within the last few thousand years. At the time of fieldwork access to the central part of the Lake Sentarum system was inhibited by strong El Niño drought conditions, but this area has the potential to provide a longer and more continuous history of environmental change for the region. Copyright © 2004 John Wiley & Sons, Ltd.
Tropical forest structure: a missing dimension to Pleistocene landscapes
Authors: Cowling Sharon A.
Published: September 2004

By focusing on the horizontal distribution of Pleistocene vegetation types within tropical landscapes, we may be overlooking an equally important feature of palaeovegetation, namely their vertical structure. Tropical forest structure is a critical factor contributing to canopy microclimatology and thus plays a role in defining canopy habitats and species population dynamics. Because of this tight relationship between forest structure and canopy microclimate, flora and fauna with narrow canopy niches may have responded to glacial reductions in forest canopy density in the same manner as if the tropical forest were completely replaced by grassland. This alternative interpretation of palaeo‐forest response to past climate change holds significance for the application of the Pleistocene refugia hypothesis in explaining various biogeographical trends. The role of forest structure in influencing hydrological cycling and the exchange of carbon between the biosphere and atmosphere are highlighted to illustrate how palaeoprecipitation and palaeoproductivity proxy data may be misinterpreted when forest structure is not explicitly considered. This is accomplished through theoretical scenarios using hydrological mass balance equations and simulations using a soil–plant–atmosphere landscape model. Available methodologies to reconstruct tropical palaeovegetation structure are identified, including the use of fully coupled earth system models. Copyright © 2004 John Wiley & Sons, Ltd.
Holocene changes of Andean alder (Alnus acuminata) in highland Ecuador and Peru
Authors: Weng Chengyu , Bush Mark B. , Chepstow‐Lusty Alex J.
Published: September 2004

Fossil pollen records from the high Andes of Ecuador and northern Peru show that Alnus increased in abundance at most sites following warming associated with the onset of the Holocene. The peak of Alnus pollen abundance occurred between ∼9000 and 5000 yr BP. However, between 6500 and 4500 yr BP, the abundance of Alnus pollen declined markedly in all of the available records, including sites both within and above its modern distribution range. Even though the beginning of this decline may have been time‐transgressive, the greatest reduction of Alnus abundance is consistent between sites, occurring at ca. 4500 yr BP. This synchrony suggests that one or more factors affected Alnus populations across the whole region. A cooler climate, droughts and anthropogenic activity are discussed as possible causes on such a large spatial scale. A scenario is suggested in which the early–mid Holocene increase in Alnus populations was curtailed by droughts, and then further impacted by major regional cooling from ca. 5000 yr BP onwards. Human agricultural activities in this wetter interval may also have delayed Alnus recovery. A resurgence of Alnus populations at 2000–1000 yr BP may have been a response to regional warming coupled with human land management practices. Copyright © 2004 John Wiley & Sons, Ltd.
A record of Late Pleistocene and Holocene carbon accumulation and climate change from an equatorial peat bog (Kalimantan, Indonesia): implications for past, present and future carbon dynamics
Authors: Page S. E. , Wűst R. A. J. , Weiss D. , Rieley J. O. , Shotyk W. , Limin S. H.
Published: September 2004

A 9.5 m core from an inland peatland in Kalimantan, Indonesia, reveals organic matter accumulation started around 26 000 cal. yr BP, providing the oldest reported initiation date for lowland ombrotrophic peat formation in SE Asia. The core shows clear evidence for differential rates of peat formation and carbon storage. A short period of initial accumulation is followed by a slow rate during the LGM, with fastest accumulation during the Holocene. Between ∼13 000 and 8000 cal. yr BP, > 450 cm of peat were deposited, with highest rates of peat (> 2 mm yr−1) and carbon (> 90 g C m−2 yr−1) accumulation between 9530 and 8590 cal. yr BP. These data suggest that Kalimantan peatlands acted as a large sink of atmospheric CO2 at this time. Slower rates of peat (0.15–0.38 mm yr−1) and carbon (7.4–24.0 g C m−2 yr−1) accumulation between ∼8000 and 500 cal. yr BP coincide with rapid peat formation in coastal locations elsewhere in SE Asia. The average LORCA (long‐term apparent carbon accumulation rate) for the 9.5 m core is 56 g C m−2 yr−1. These data suggest that studies of global carbon sources, sinks and their dynamics need to include information on the past and present sizeable peat deposits of the tropics. Copyright © 2004 John Wiley & Sons, Ltd.
Block‐Selective Solvent Influence on Morphology of the Micelles Self‐Assembled by PS38‐b‐P(AA190‐co‐MA20)
Authors: Zhang Wangqing , Shi Linqi , An Yingli , Gao Lichao , Wu Kai , Ma Rujiang , Zhang Banghua
Published: September 2004

Summary: The influence of block‐selective solvent on the self‐assembly of polystyrene‐block‐poly[(acrylic acid)‐co‐(methyl acrylate)] was studied. The nature of the block‐selective solvent, which is a binary solvent mixture with different composition, exerts remarkable influence on the morphology of the resulting micelles. When the block‐selective solvent is a binary solvent mixture of acetone and water with acetone content ranging from 0 to 90 vol.‐%, the resulting aggregates are core‐shell spheres with diameter about 60 nm, porous aggregates with diameter of 100, 180 and 250 nm, and core‐shell cauliflower‐like aggregates with size about 200 nm, respectively. The reason that the morphology of resulting micelles changes with acetone content has been discussed. The structure of the resulting micelles is further characterized in detail by DLS and SLS. Morphological tuning is also achieved by using a binary solvent mixture of ethanol and water or a binary solvent mixture of DMF and water as block‐selective solvent. In these cases, core‐shell spheres, hollow aggregates, and incompact aggregates are formed with the ethanol or DMF concentration ranging from 10 to 80 vol.‐%.

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Crosslinked Polyacrolein Microspheres with High Loading of Aldehyde Groups for Use as Scavenger Resins in Organic Synthesis
Authors: Lin Chao , Zhang Zhengpu , Zheng Jianfen , Liu Miaomiao , Zhu Xiao Xia
Published: September 2004

Summary: Suspension polymerization yielded microspheres (40–50 μm) of polyacrolein. Smooth and rugged surfaces can be created by varying the polymerization procedure. We have shown that the polyacrolein resins with a high loading of aldehyde groups serve as effective scavengers for primary amines and may be used to remove compounds bearing amino groups in the combinatorial synthesis of compound libraries. Copolymerization with styrene can help to separate the adjacent aldehyde groups, thus making the functional groups more available in organic reactions. The polyacrolein resins in the aldehyde form or after appropriate chemical modifications may also be useful as support materials in solid‐phase synthesis.

The SEM image of macroporous polyacrolein microspheres with toluene as porogen prepared by free radical polymerization.

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The SEM image of macroporous polyacrolein microspheres with toluene as porogen prepared by free radical polymerization.
Variation of the Effective Activation Energy Throughout the Glass Transition
Authors: Vyazovkin Sergey , Sbirrazzuoli Nicolas , Dranca Ion
Published: September 2004

Summary: An advanced isoconversional method has been applied to determine the effective activation energies (E) for the glass transition in polystyrene (PS), poly(ethylene terephthalate) (PET), and boron oxide (B2O3). The values of E decrease from 280 to 120 kJ · mol−1 in PS, from 1 270 to 550 kJ mol−1 in PET, and from 290 to 200 kJ mol−1 in B2O3. It is suggested that a significant variation in E should be observed for the fragile glasses that typically include polymers.

Variation in the effective activation energy of PS, PET, and B2O3 with temperature.

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Variation in the effective activation energy of PS, PET, and B2O3 with temperature.
A New View of the Anionic Diene Polymerization Mechanism
Authors: Niu A.Z. , Stellbrink J. , Allgaier J. , Willner L. , Richter D. , Koenig B.W. , Gondorf M. , Willbold S. , Fetters L.J. , May R.P.
Published: September 2004

We investigated the anionic polymerization of butadiene in d‐heptane solvent using tert‐butyl lithium as initiator. Two complementary techniques were used to follow the polymerization processes: 1H NMR and small angle neutron scattering (SANS). The time resolved 1H NMR measurements allowed us to evaluate quantitatively the kinetics of the processes involved. The initiation event commences slowly and then progressively accelerates. This indicates an autocatalytic mechanism. The microstructure of the first monomer units attached is to a high extent 1,2. The disappearance of initiator ‐‐‐ at about 10% monomer conversion ‐‐‐ signals the onset of the normal ∼6% vinyl content of the chain. Small angle neutron scattering was used to study the aggregation behavior of the carbon lithium head groups. It is well known that the polar head groups aggregate and form micellar structures. For dienes in non‐polar solvents the textbook mechanism assumes the formation of only tetramers during the propagation reaction. By combining 1H NMR and SANS results we were able to determine quantitatively the aggregation number during all stages of the polymerization. Our measurements show the existence of large‐scale structures during the initiation period. The initial degree of aggregation of more than 100 living polymer chains diminished as the polymerization progressed. In addition, even larger, giant structures with Nagg >>1000 and Rg ≈ 1000Å were found.
Aluminate and Magnesiate Complexes as Propagating Species in the Anionic Polymerization of Styrene and Dienes
Authors: Deffieux Alain , Shcheglova Larisa , Barabanova Anna , Maréchal Jean Marc , Carlotti Stephane
Published: September 2004

The influence of MgR2 and AlR3 additives on alkyllithium initiators in the anionic polymerization of butadiene has been investigated in non polar solvents. A strong decrease of the diene polymerization rate in the presence of the two Lewis acids was observed, similarly to that observed in the retarded anionic polymerisation of styrene. With n,s‐Bu2Mg, the percentage of 1,2 vinyl units increases with the [Mg]/[Li] ratio. This behavior is specific to magnesium derivatives bearing secondary alkyl groups and likely results from the additional complexation of lithium species by free dialkylmagnesium and/or a 1,4‐ to 1,2‐ chain end isomerization process during chain exchanges between polybutadienyl active chains and dormant ones attached to magnesium species. These reversible exchanges also lead to the formation of one supplementary chain by initial dialkyl magnesium which acts as reversible chain transfer agent. On the contrary with the R3Al/RLi systems the number of chains is only determined by the concentration of initial alkyllithium and no modification of the polybutadiene microstructure compared to lithium initiators (1,4 units = 80%) is noticed.

Dialkyl magnesiate complexes with alkali metal derivatives (i.e. alkoxide) are also able to influence the stereochemistry of the styrene insertion during the propagation reaction. Polystyrenes with different tacticities ranging from predominantly isotactic (85% triad iso) to syndiotactic (80% triad syndio) can be obtained with these initiators.
Design and Synthesis of Functionalized Styrene‐Butadiene Copolymers by Means of Living Anionic Polymerization
Authors: Hayashi Mayumi
Published: September 2004

Styrene‐butadiene copolymers (SBR) end‐functionalized with dimethylamino groups at the initiating and terminating chain‐ends were successfully synthesized by a one‐step methodology based on living anionic polymerization using 1‐(4‐dimethylaminophenyl)‐1‐phenylethylene. The expected structures of the resulting copolymers were confirmed by 1H‐NMR, SEC, and SLS analyses, titration, and model reactions. Furthermore, the possible synthesis of tri‐functionalized styrene‐butadiene copolymer with dimethylamino groups in a chain by extending the methodology is described.
Synthesis of PS Star Polymers from Tetracarbanionic Initiators
Authors: Lebreton Arnaud , Kallitsis J.K. , Héroguez Valérie , Gnanou Yves
Published: September 2004

A novel tetracarbanionic initiator as designed and used to obtain star polymers. Well‐defined four‐arm polystyrene stars exhibiting expected molar masses and low polydispersity indexes have been obtained in this way.
Fluorinated Amphiphilic Block Copolymers: Combining Anionic Polymerization and Selective Polymer Modification
Authors: Hillmyer Marc A. , Schmuhl Nathan W. , Lodge Timothy P.
Published: September 2004

We report the preparation of novel fluorinated block copolymers using a two‐step modification sequence. We first prepared model polyisoprene‐poly‐tert‐butylmethacrylate block copolymers by anionic polymerization. Exposing these materials to difluorocarbene (generated by the thermolysis of hexafluoropropylene oxide) resulted in modification of the polyisoprene block to the corresponding difluorocyclopropane repeating unit without compromising the integrity of the poly‐tert‐butylmethacrylate block. Hydrolysis of the difluorocarbene‐modified materials gave the corresponding difluorocarbene‐modified polyisoprene‐polymethacrylic acid diblock copolymers. These amphiphilic materials are expected to exhibit interesting self‐assembly behavior in aqueous solution.
Precise Synthesis of Star‐Branched Polymers by Means of Living Anionic Polymerization Using 1,1‐Bis(3‐chloromethylphenyl)ethylene
Authors: Hirao Akira , Higashihara Tomoya
Published: September 2004

The syntheses of three‐ and four‐arm star‐branched polymers by a new convenient methodology using 1,1‐bis(3‐chloromethylphenyl)ethylene are described. The methodology involves only two sets of reactions: an addition reaction of living anionic polymer to 1,1‐bis(3‐chloromethylphenyl)ethylene and a linking reaction of the intermediate polymer anion with ω‐4‐bromobutyl‐functionalized polymer. All combinations of well‐defined three‐ and four‐arm stars comprised of polystyrene and polyisoprene segments were successfully synthesized by this methodology.
Synthesis and Properties of Macrocyclic Vinylaromatic Polymers Containing a Single 1,4‐Benzylidene or 9,10‐Anthracenylidene Group
Authors: Chen Rong , Nossarev Gennadi G. , Hogen‐Esch Thieo E.
Published: September 2004

The synthesis is reported of well‐defined and narrow molecular weight distribution macrocyclic poly(2‐vinylnaphthalene) (P2VN) and poly(9,9‐dimethyl‐2‐vinylfluorene) (PDMVF) containing a single 1,4‐benzylidene or 9,10‐anthracenylidene unit. The synthesis involves the potassium naphthalide (K‐Naph) initiated polymerization of 2VN or DMVF in THF at −78 °C followed by end‐to‐end coupling of the resulting P2VN dianions under high dilution conditions (10−6‐10−4 M) with 1,4‐bis(bromomethyl)benzene (DBX) or 9,10‐bis(chloromethyl)anthracene (BCMA). The molecular characterization was carried out by size exclusion chromatography (SEC), NMR and MALDI‐TOF.
Synthesis and Structure – Property Relationships for Regular Multigraft Copolymers
Authors: Mays Jimmy W. , Uhrig David , Gido Samuel , Zhu Yuqing , Weidisch Roland , Iatrou Hermis , Hadjichristidis Nikos , Hong Kunlun , Beyer Frederick , Lach Ralf , Buschnakowski Matthias
Published: September 2004

Multigraft copolymers with polyisoprene backbones and polystyrene branches, having multiple regularly spaced branch points, were synthesized by anionic polymerization high vacuum techniques and controlled chlorosilane linking chemistry. The functionality of the branch points (1, 2 and 4) can be controlled, through the choice of chlorosilane linking agent. The morphologies of the various graft copolymers were investigated by transmission electron microscopy and X‐ray scattering. It was concluded that the morphology of these complex architectures is governed by the behavior of the corresponding miktoarm star copolymer associated with each branch point (constituting block copolymer), which follows Milner's theoretical treatment for miktoarm stars. By comparing samples having the same molecular weight backbone and branches but different number of branches it was found that the extent of long range order decreases with increasing number of branch points. The stress‐strain properties in tension were investigated for some of these multigraft copolymers. For certain compositions thermoplastic elastomer (TPE) behavior was observed, and in many instances the elongation at break was much higher (2‐3X) than that of conventional triblock TPEs.
Mechanism of the Anionic Ring‐Opening Oligomerization of Propylene Carbonate Initiated by the tert‐Butylphenol/KHCO3 System
Authors: Kéki Sándor , Török János , Deák György , Zsuga Miklós
Published: September 2004

The ring‐opening oligomerization reaction of propylene carbonate in the presence of the tert‐butylphenol/KHCO3 initiating system was studied by means of Matrix‐Assisted Laser Desorption/Ionization Time of Flight Mass Spectrometry (MALDI‐TOF MS) and Electrospray Ionization Time of Flight Mass Spectrometry (ESI‐TOF MS). According to the MS spectra obtained, different series of peaks were identified. The MS spectra clearly showed that besides the chain‐extension reaction yielding oligomers with all propylene oxide units, the formation of oligomers containing carbonate linkages in the chain, and condensation reaction between the latter two also took place. The structure of the oligomers carrying carbonate linkages was determined by the post‐source decay (PSD) MALDI‐TOF MS/MS method. Based on the MS results, a mechanism for the oligomerization reaction is proposed.
Synthesis and Self‐Association of Stimuli‐Responsive Diblock Copolymers by Living Cationic Polymerization
Authors: Aoshima Sadahito , Sugihara Shinji , Shibayama Mitsuhiro , Kanaoka Shokyoku
Published: September 2004

The living cationic polymerization of several functional monomers in the presence of an added base is investigated as a possible preparation of a new series of water‐soluble or stimuli‐responsive copolymers. Under appropriate conditions, the polymerization allows the selective preparation of polymers with various shapes and different sequence distributions of monomer units, including stimuli‐responsive block copolymers, gradient copolymers, poly(vinyl alcohol) graft copolymers, and star‐shaped polymers. The stimuli‐induced self‐association of the diblock copolymers is also examined. An aqueous solution of the diblock copolymer with a thermo‐sensitive segment undergoes rapid physical gelation upon warming to the critical temperature to give a transparent gel, and returns sensitively to the solution state upon cooling. The sharp transition of stimuli‐responsive segments with highly controlled primary structure turns out to play an important role in the self‐association. Small‐angle neutron scattering, dynamic light scattering, and electron microscopy studies reveal that the physical gelation involves a thermosensitive micellization of diblock copolymers (core size: 18‐20 nm) and subsequent micelle macrolattice formation (bcc symmetry). Based on the gelation mechanism, several stimuli‐responsive gelation systems are achieved using other stimuli such as the addition of a selective solvent or compound, cooling, pH change, and irradiation with ultraviolet light.
Advances in the Design of Photoinitiators, Photo‐Sensitizers and Monomers for Photoinitiated Cationic Polymerization
Authors: Crivello J.V. , Ma J. , Jiang F. , Hua H. , Ahn J. , Acosta Ortiz R.
Published: September 2004

The present article reports on recent work from this laboratory that has led to advances in several areas of the field of photoinitiated cationic polymerization. Two different classes of novel photoinitiators 5‐arylthianthrenium salts and 4‐hydroxyphenyl dialkylsulfonium salts have been prepared and their use in the polymerization of various monomer systems studied. Also described is the development of both monomeric and polymeric photosensitizers that may be employed to broaden the spectral sensitivity of various onium salt photoinitiators. Acceleration of rate of the ring‐opening polymerization of epoxide monomers has been achieved through the use of benzyl alcohols. Further, benzyl alcohols bearing sensitizing groups were found to be especially interesting as combination accelerators‐photosensitizers. Lastly, epoxy monomers having groups with easily abstractable protons display exceptional reactivity in photoinitiated ring‐opening cationic polymerization. A mechanism has been proposed to explain this observation.
On the Preparation and Polymerization of p‐Methoxystyrene Miniemulsions in the Presence of Excess Ytterbium Triflate
Authors: Cauvin Séverine , Ganachaud François
Published: September 2004

The cationic polymerization of p‐methoxystyrene using an acid initiator and ytterbium triflate as a cocatalyst was studied in miniemulsion. Conductometry measurements revealed that ytterbium triflate dissociates in water. The high ionic strength implemented by ytterbium cation releasing requires the use of an electrosteric surfactant, i.e. sodium dodecylpolyoxyethylene(8) sulfate, as an efficient stabilizer against particle coalescence. The catalyst increases significantly the polymerization rate but only moderately affects the molar masses. A tentative polymerization scheme is proposed based on these results and several other åblankα experiments.
Carbocationic Polymerizations for Profit and Fun
Authors: Peetz Ralf M. , Kennedy Joseph P.
Published: September 2004

This presentation consists of two largely independent parts: The first åfor Profitα part concerns a bird's eye view of recently commercialized carbocationic processes and materials created by these processes in the author's laboratories whose marketing started during the past ∼5 years by various companies. These materials/processes include liquid telechelic polyisobutylene (PIB) for architectural sealants, poly(styrene‐b‐isobutylene‐b‐styrene) (PSt‐b‐PIB‐b‐PSt) triblocks for thermoplastic elastomers, PIB/PSt‐based blocks for coating of medical devices, and PIB‐based microemulsions for surface protection of painted metal surfaces. It is concluded that in order to enhance and solidify research in polymer synthesis it would behoove the scientific community to pay increased attention to intellectual property protection. Appropriately managed patenting and publishing activities are self‐reinforcing and may be quite profitable.

The second “for Fun” part concerns a brief review of the design, synthesis and characterization of two novel fully aliphatic star‐block copolymers: ∅︁(PIB‐b‐PNBD)3 and ∅︁(PNBD‐b‐PIB)3 (where PNBD = polynorbornadiene). The constituent moieties of these star‐blocks are identical except their block sequences are reversed. Motivation for the synthesis of ∅︁(PIB‐b‐PNBD)3, consisting of a low Tg (∼‐73°C) PIB inner‐corona attached to a high Tg (∼320°C) PNBD outer corona, was the expectation that this star‐block would exhibit thermoplastic elastomer characteristics, and that it could be used in applications where similar polyaromatic‐based TPEs cannot be employed (e.g., magnetic signal storage). The other star‐block, ∅︁(PNBD‐b‐PIB)3, comprises the same building blocks with the PIB and PNBD sequences reversed. We found that the secondary chlorine at the PNBD chain end, in conjunction with TiCl4, is able to initiate the polymerization of isobutylene. Details of the carbocationic polymerization of NBD, together with the microstructure of PNBD, will be discussed.
Comparison of the Mechanism and Kinetics of Living Carbocationic Isobutylene and Styrene Polymerizations Based on Real‐Time FTIR Monitoring
Authors: Puskas Judit E. , Shaikh Sohel
Published: September 2004

This paper will compare the mechanism and kinetics of living carbocationic polymerization of isobutylene (IB) and styrene (St), initiated by the 2‐chloro‐2,4,4‐trimethyl‐pentane (TMPCl) / TiCl4) system in 60/40 (v/v) methylcyclohexane / methyl chloride mixed solvent at −80 and −75 °C. The rate of initiation was found to be first order in TiCl4 in both systems. While initiation is instantaneous in IB polymerization at [TiCl4]0 ⩾ [TMPCl]0, it is slow in St polymerization. Kinetic derivation showed that initiating efficiency is dependent on [M] in this latter system, which was also demonstrated experimentally. The apparent initiation rate constant was determined from initiator consumption rate data and was found to be ki,app = 1.39 l2/mol2sec. The rate of St consumption measured using a real time fibre‐optic mid‐FTIR monitoring technique compared well with gravimetric data and was found to be closer to first order in TiCl4 at [TiCl4]0 < [TMPCl]0. However, the rate followed a close to second order in TiCl4 at [TiCl4]0 ⩾ [TMPCl]0. The mechanistic model proposed earlier for living carbocationic IB polymerization, which yielded good agreement with experimental data, seems to apply to carbocationic St polymerization as well. This model reconciles the discrepancy between rate constants published for carbocationic IB and St polymerizations, and accounts for shifting TiCl4 orders. However, independent investigations are necessary to verify the proposed mechanistic model. Optimized conditions led to living carbocationic St polymerization producing high molecular weight PS with 100% initiating efficiency.
Novel Cationic Ring‐Opening Polymerization of Cyclodextrin: A Uniform Macrocyclic Monomer with Unique Character
Authors: Suzuki Masato , Numata Osamu , Shimazaki Tomofumi
Published: September 2004

Cyclodextrin (CD) derivatives were found to act as uniform macrocyclic monomers for cationic ring‐opening polymerization, yielding poly[(1→4)‐D‐glucopyranoside]s. Interestingly, as demonstrated in the polymerization of O‐permethylated α‐, β‐, and γ‐CDs, more strained monomer (α‐ > β‐ > γ‐) proved less reactive. This finding comes from the unique molecular shape of CD; the monomer having larger cavity (γ‐ > β‐ > α‐) is favorable for the polymerization. In place of ordinary initiators such as oxonium salts and MeOTf, a combination of HI with an activator of ZnCl2 was found to work as the initiator effectively controlling the polymerization; the glucan obtained from O‐permethylated γ‐CD showed a unique molecular weight distribution, which has large, regular intervals corresponding to the molecular weight of the uniform macrocyclic monomer (= 1634).
Wavelength Flexibility in Photoinitiated Cationic Polymerization
Authors: Yagci Yusuf
Published: September 2004

The spectral sensitivity of onium salt photoinitiators in cationic polymerization can be tuned from the short wavelength region of the UV spectrum to wavelengths up to the visible region by using direct and indirect activation, respectively. Indirect activation is based on the electron transfer reactions between onium salts and free radical photoinitiators, appropriate sensitizers and compounds capable of forming charge transfer complexes. Bisacylphosphine oxides, dimanganese decacarbonyl in conjunction with alkyl halides and titanocene type photoinitiators such as Irgacure 784 were shown to be useful free radical promoters providing the possibility of performing cationic polymerization in the long wavelength and visible region. The synthetic routes to prepare block copolymers by using electron transfer photosensitization and free radical promoted cationic polymerization are also described.
Ring‐Opening Polymerization of the Cyclic Ester Amide Derived from Adipic Anhydride and 1‐Amino‐6‐hexanol in Melt and in Solution
Authors: Fey Thomas , Keul Helmut , Höcker Hartwig
Published: September 2004

The ring‐opening polymerization (ROP) of the cyclic ester amide (cEA) 5 (systematic name, 1‐oxa‐8‐aza‐cyclotetradecane‐9,14‐dione) ‐ prepared from adipic anhydride and 1‐amino‐6‐hexanol ‐ in the melt at 165 °C and in solution at 100 °C and 120 °C with Bu2Sn(OMe)2 or Ti(OBu)4 as initiator yields the alternating poly(ester amide) (PEA) 4 (systematic name, poly(5‐(6‐oxyhexylcarbamoyl)‐pentanoate) with regular microstructure. Kinetic studies for different monomer‐to‐initiator ratios, different reaction media, initiators and temperatures reveal that the ROP is a first‐order reaction with respect to the monomer. Under suitable polymerization conditions termination and transfer reactions are suppressed. The elementary chain growth reaction proceeds by a coordination insertion mechanism in analogy to the polymerization of lactones. By using monohydroxy‐ and bishydroxy‐functional telechelic poly(ethylene oxide) and Sn(octoate)2 as the initiating system poly(ethylene oxide)‐block‐poly(ester amide)s and poly(ester amide)‐block‐poly(ethylene oxide)‐block‐poly(ester amide)s are obtained. The poly(ester amide) 4 is a semicrystalline material with a melting point of 140 °C, the block copolymers are phase separated systems showing two melting points characteristic for the respective homopolymers.
Recent Developments in the Ring‐Opening Polymerization of ϵ‐Caprolactone and Derivatives Initiated by Tin(IV) Alkoxides
Authors: Lecomte Ph. , Stassin F. , Jérôme R.
Published: September 2004

The macromolecular engineering of aliphatic polyesters by ring‐opening polymerization (ROP) initiated by aluminum alkoxides is now well established. Tin (IV) alkoxides are less popular, mainly because of a poorer control of the chain growth. This paper discusses some recent examples from CERM, showing that tin (IV) alkoxides can advantageously replace the aluminum counterparts as ROP initiators. For instance, they can initiate successfully the Ring‐Opening Polymerization of α‐chloro‐ϵ‐caprolactone and dioxepane‐2‐one. They are also very promising initiators for ROP in supercritical CO2 and for the synthesis of clay/aliphatic polyester nanocomposites.
Functionalization of Living Polymers via Ethoxysilane Based Compounds: Synthesis and Interaction with Silica Particles
Authors: Hoffstetter Joël , Giebeler Ellen , Peter Rolf , Lutz Pierre J.
Published: September 2004

To optimize the reaction of ω‐carbanionic styrene or butadiene/styrene polymers with ethoxysilane based compounds, the influence of several experimental parameters on the orientation of the functionalization reaction and its yield was examined. The resulting end‐functionalized polymers were systematically investigated by SEC, 1H NMR and elementary analysis. The orientation of the reaction was found to be directly depending on the chemical nature of the chain end and / or on the type of additive (ethers, LiCl). Best results were obtained with tetraethoxysilane, provided the functionalization is conducted around 5°C, and the active chain end of isoprenyl type. These reactions were extended to bifunctional polymers, the reaction product of butyllithium with m‐diisopropenylbenzene being used as an initiator. The efficiency of this initiator for the synthesis of well‐defined bifunctionalized polydienes almost quantitatively fitted with three alkoxy functions at both chain ends was demonstrated. Some preliminary results on the mechanical properties of mixtures of functionalized polymers with silica were mentioned.
Reactivities of Carbocations and Carbanions
Authors: Ofial Armin R. , Mayr Herbert
Published: September 2004

Initiation and propagation rate constants of carbocationic and carbanionic polymerizations can be predicted by the correlation equation log k20 °C = s(N + E), where E characterizes the electrophilicity of carbocations and electron‐deficient alkenes, and N characterizes the nucleophilicity of carbanions and electron‐rich alkenes. Since the nucleophile‐specific slope parameter s is generally close to 1, it can be neglected in a first approximation, and the two‐dimensional representation in Figure 3 illustrates the gradual change from carbanionic to carbocationic polymerizations with Hall's “initiation by bond‐formation” as the link connecting the two ranges. The value of model studies for understanding ionic polymerizations is illustrated.
Confinement Effects on the Crystallization Kinetics and Self‐Nucleation of Double Crystalline Poly(p‐dioxanone)‐b‐poly(ϵ‐caprolactone) Diblock Copolymers
Authors: Müller Alejandro J. , Albuerne Julio , Esteves Luis M. , Marquez Leni , Raquez Jean‐Marie , Degée Philippe , Dubois Philippe , Collins Stephen , Hamley Ian W.
Published: September 2004

The morphology, crystallization and self nucleation behavior of double crystalline diblock copolymers of poly(p‐dioxanone) (PPDX) and poly(ϵ‐caprolactone) (PCL) with different compositions have been studied by different techniques, including optical microscopy (OM), atomic force microscopy (AFM) and differential scanning calorimetry (DSC). The two blocks crystallize in a single coincident exotherm when cooled from the melt. The self‐nucleation technique is able to separate into two exotherms the crystallization of each block. We have gathered evidences indicating that the PPDX block can nucleate the PCL block within the copolymers regardless of the composition. This effect is responsible for the lack of homogeneous nucleation or fractionated crystallization of the PCL block even when it constitutes a minor phase within the copolymer (25% or less). Nevertheless, we were able to show that decreasing amounts of PCL within the diblock copolymer still produces confinement effects that retard the crystallization kinetics of the PCL component and decrease the Avrami index. On the other hand evidence for confinement was also obtained for the PPDX block, since as its content is reduced within the copolymer, a depression in its self‐nucleation and annealing temperatures were observed.
Advances in the Synthesis and Characterization of Polypeptide‐Based Hybrid Block Copolymers
Authors: Dimitrov Ivaylo , Kukula Hildegard , Cölfen Helmut , Schlaad Helmut
Published: September 2004

Linear polystyrene‐block‐poly(Z‐L‐lysine) copolymers with a very narrow molecular weight distribution (polydispersity index < 1.03) could be obtained via the ring‐opening polymerization of Z‐L‐lysine‐N‐carboxyanhydride using ω‐(primary amino hydrochloride)‐polystyrenes as macroinitiators in N,N‐dimethylformamide as the solvent at 40‐80 °C. The block copolymer samples were analyzed by means of NMR, size exclusion chromatography, and analytical ultracentrifugation.
Novel microwave microstrip filters using photonic bandgap ground plane with fractal periodic pattern
Authors: Siakavara K.
Published: September 2004

Photonic bandgap (PBG) structures with slots etched in their ground plane have been proposed recently as a good choice for the design of printed microwave filters, absorbers, reflectors, and antennas for many modern applications. In the present work, a microstrip PBG filter was designed to operate as a multifrequency bandstop filter. The conventional profile of the slot patterns used in previous works was either discrete (with circles), continuous sinusoidal, or triangular. These geometries guide the structure to operate as a single wideband filter. In this work, a different periodic pattern of slots is introduced. The configuration is designed using the fractal technique. The self‐similarity of the fractal geometry is found to excite the PBG structure to act as a wide stop‐band filter in more than one frequency region. © 2004 Wiley Periodicals, Inc. Microwave Opt Technol Lett 43: 273–276, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.20443
Triangular microstrip array on NiZn substrate in the L‐band
Authors: Kumar Dheeraj , Pourush P. K. S.
Published: September 2004

The radiation characteristics of a microstrip planar array of triangular patch antennas printed on NiZn ferrite substrate with a normal magnetic bias field are described. The extra degree of freedom offered by the biased ferrite can be used to obtain a number of novel characteristics, including switchable and tunable radiations from a microstrip antenna with a single feed point. In such a case, for antenna radiation, most of the power is converted into magnetostatic waves and little power radiates in the air. Under such circumstances, the antennas are off, in the sense that they are effectively absent as radiators. The radiation properties of the present array system in the L‐band (2 GHz) are analyzed. © 2004 Wiley Periodicals, Inc. Microwave Opt Technol Lett 43: 286–290, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.20447
A study of planar Goubau lines (PGLs) for millimeter‐ and submillimeter‐wave integrated circuits (ICs)
Authors: Xu Yansheng , Bosisio Renato G.
Published: September 2004

In this paper, a new type of planar Goubau line (PGL) for millimeter‐ and submillimeter‐wave applications is proposed for use in wideband integrated circuits. The configurations of these modified Goubau lines are examined and the parameters are provided. The performances of these lines are studied in detail. Characteristics of lines with different dimensions are calculated and displayed. Comparisons with other types of transmission lines are also performed. © 2004 Wiley Periodicals, Inc. Microwave Opt Technol Lett 43: 290–293, 2004; Published online in Wiley InterScience (www.interscience.wiley.com).
An active receiving antenna for short‐range wireless automotive communication
Authors: Al‐Khateeb Basim , Rabinovich Victor , Oakley Barbara
Published: September 2004

This paper describes an easily manufactured, reduced‐size, active receiving antenna for automotive applications, which increases short‐range wireless detection in the 315‐MHz band. This compact antenna has an advantage over currently available antennas because can be hidden in a vehicle's interior. The active antenna consists of a low‐noise amplifier coupled to a low‐profile planer meander‐line pattern printed on the dielectric substrate. Experimental verification of the antenna performance and a theoretical calculation for the maximum range of the active antenna are presented. © 2004 Wiley Periodicals, Inc. Microwave Opt Technol Lett 43: 293–297, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.20448
Multiwavelength ring lasers employing semiconductor optical amplifiers as gain media
Authors: Sun Junqiang
Published: September 2004

Stable simultaneous multiwavelength lasing is demonstrated with a novel fiber‐ring laser incorporating a semiconductor optical amplifier. Band‐pass comb filtering is constructed in the ring cavity with the combination of a wideband Fabry–Perot comb filter and a bandpass filter. Ten lasing lines with a fixed wavelength spacing of 1.6 nm are implemented and the multiwavelength lasing ranges can be flexibly chosen. © 2004 Wiley Periodicals, Inc. Microwave Opt Technol Lett 43: 301–303, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.20451
A fast calculation of impedances of dipoles near cylindrical structure by applying asymptotic waveform evaluation in a spectrum of 2D solutions
Authors: Yang Jian , Kildal Per‐Simon
Published: September 2004

A spectrum of 2D solutions (S2DS) applies the Fourier transform to 3D currents in the uniform direction of a 2D cylindrical structure to arrive into a spectral‐domain problem which can be solved by 2D spatial techniques. In order to calculate the near fields that are needed for the calculation of impedance, the inverse Fourier transform must be performed. This usually requires a large number of 2D solutions in the spectral domain. By using the asymptotic waveform evaluation (AWE) method in S2DS, the inverse Fourier transform can be performed very efficiently, with only several 2D solutions in the spectral domain. This paper presents the fast calculation of the impedance of a dipole in the vicinity of a 2D cylindrical structure. The cases presented in this paper show that the calculation is accelerated seven times more than by using the direct S2DS method. © 2004 Wiley Periodicals, Inc. Microwave Opt Technol Lett 43: 314–317, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.20455
FDTD analysis of a symmetric T‐strip fed wideband rectangular microstrip antenna
Authors: Lethakumary B. , Menon Sreedevi K. , Aanandan C. K. , Vasudevan K. , Mohanan P.
Published: September 2004

A theoretical analysis of a symmetric T‐shaped microstrip‐fed rectangular microstrip antenna using the finite‐difference time‐domain (FDTD) method is presented in this paper. The resonant frequency, return loss, impedance bandwidth, and radiation patterns are predicted and are in good agreement with the measured results. © 2004 Wiley Periodicals, Inc. Microwave Opt Technol Lett 43: 332–334, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.20461
Technological evolution and performances improvements of a tunable phase‐shifter using liquid crystal
Authors: Martin Noham , Laurent Paul , Prigent Gaëtan , Gelin Philippe , Huret Fabrice
Published: September 2004

The topic of this paper is the study of electrically tunable phase‐shifters based on the use of liquid crystals. The dielectric characterization of the commercial liquid crystal involved in this study allows us to determine its dielectric permittivities (with and without DC voltage applied) and then its dielectric anisotropy. In this way, two phase‐shifter configurations were studied. Every devices propose inverted microstrip line. The two circuits have been realized with coplanar accesses to be use in the millimeter‐frequency range. With the aim to improve the phase shift parameter (in °/GHz/cm), our work aims to reduce the transmission line. Instead of a rectilinear transmission line, this one is based on a symmetric stub line. The phase shift obtained is enhanced from 0.87°/GHz/cm to 2.77°/GHz/cm. © 2004 Wiley Periodicals, Inc. Microwave Opt Technol Lett 43: 338–341, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.20463
Effect of spherical aberration on the coupling efficiency between a laser diode and a hemispherically lensed tapered fiber
Authors: Kumaran S. , Faidz A. R.
Published: September 2004

The objective of our work is to conduct a theoretical analysis to determine the coupling efficiency between a laser diode (LD) and a hemispherically lensed tapered single‐mode fiber (SMF), which takes into account the effect of spherical aberration on the lens surface. The results obtained clearly show that our proposed theoretical method provides a good estimation of the experimental data. © 2004 Wiley Periodicals, Inc. Microwave Opt Technol Lett 43: 341–343, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.20464
Analog predistorter using a Cartesian vector modulator structure
Authors: Jang Dong‐Hee , Cho Kyung‐Joon , Kim Sang‐Hee , Kim Ji‐Yeon , Kim Jong‐Heon , Stapleton Shawn P.
Published: September 2004

We propose an analog predistorter that uses a Cartesian vector modulator structure. The operation principle of the proposed predistorter is analyzed for various gain and phase characteristics. The bandwidth performance of the predistorter is presented as a function of the dominant nonlinearity order. Experiments on several power amplifiers under various test signals were performed on the proposed analog predistorter. The experimental results demonstrate that the predistorter can easily control both the gain and phase characteristics via biasing the two IM generators. © 2004 Wiley Periodicals, Inc. Microwave Opt Technol Lett 43: 343–348, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.20465
Accurate characterization of MEM inductors on lossy silicon
Authors: Lee Young‐Ho , Lee Sang‐No , Yook Jong‐Gwan , Kim Ji‐Hyuk , Chun Kuk‐Jin
Published: September 2004

This paper presents the performance characteristics of an air‐suspended high‐Q MEM inductor that is characterized based on an open‐short deembedding scheme and used for accurate and reliable evaluation of the parasitic effects experienced from feed lines as well as contact pads. The validity and effectiveness of the de‐embedding method are proven with a fixed‐length MEM transmission line along with various feed‐line topologies. The measured inductances of the 20‐μm elevated transmission line provide consistent data, as compared to the simpler open de‐embedding method. For more realistic and complicated MEM inductors with 1.5 and 2.5 turns, the characterized inductance values agree very well with the calculated data, based on the Greenhouse algorithm. The measured and calculated inductances are within the 5% range. © 2004 Wiley Periodicals, Inc. Microwave Opt Technol Lett 43: 355–358, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.20468
Brachial plexopathies: Classification, causes, and consequences
Authors: Ferrante Mark A.
Published: September 2004

The brachial plexus, which is the most complex structure of the peripheral nervous system, supplies most of the upper extremity and shoulder. The high incidence of brachial plexopathies reflects its vulnerability to trauma and the tendency of disorders involving adjacent structures to affect it secondarily. The combination of anatomic, pathophysiologic, and neuromuscular knowledge with detailed clinical and ancillary study evaluations provides diagnostic and prognostic information that is important to clinical management. Since most brachial plexus disorders do not involve the entire brachial plexus but, rather, show a regional predilection, a regional approach to assessment of plexopathies is necessary. Muscle Nerve, 2004