bluuebunny/crossref_metadata_2025_split huggingface dataset:
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

AbstractA 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

AbstractSummary: 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

AbstractSummary: 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.imageThe 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

AbstractSummary: 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.imageVariation 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

AbstractWe 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

AbstractThe 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

AbstractStyrene‐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

AbstractA 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

AbstractWe 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

AbstractThe 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

AbstractThe 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

AbstractMultigraft 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

AbstractThe 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

AbstractThe 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

AbstractThe 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

AbstractThe 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

AbstractThis 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

AbstractThis 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

AbstractCyclodextrin (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).