bluuebunny/crossref_metadata_2025_split huggingface dataset:
Improved Electro‐Optic Effect by Hyperbranched Chromophore Structures in Side‐Chain Polyimide
Authors: Do Jung Y. , Park Seung K. , Ju Jung‐Jin , Park Suntak , Lee Myung‐Hyun 
Published: June 2004

AbstractHyperbranched structures of chromophores were developed to improve the nonlinearity of optical polymers. Macromolecules with 3‐[p‐(2′‐hydroxyethylmethylamino)styryl]‐1‐dicyanomethylene‐5,5‐dimethylcyclohex‐2‐ene (AIDC) were prepared using 3,5‐dihydroxyphenyl groups as building blocks. When the molecule was incorporated into a polyimide backbone (PI‐DAIDC101), a high electro‐optic coefficient was obtained, giving 32 pm · V−1 at 1.55 μm. The nonlinearity is at least doubly enhanced in comparison with that of conventional side chain‐optical polyimides. This is mainly attributable to an increased polarizing efficiency derived from the chromophore structures.
The structure of the linear polyimide backbone (PI‐OH) and the chromophore‐attached optical polyimide (PI‐DAIDC101).imageThe structure of the linear polyimide backbone (PI‐OH) and the chromophore‐attached optical polyimide (PI‐DAIDC101).
Shear‐Induced Crystallization and Shear‐Induced Dissolution of Poly(ethylene oxide) in Mixtures with Tetrahydronaphthalene and Oligo(dimethyl siloxane‐b‐ethylene oxide)
Authors: Madbouly Samy A. , Wolf Bernhard A. 
Published: June 2004

AbstractCloud point temperatures (Tcp) and crystallization temperatures (Tl/s) were measured at different constant shear rates for the ternary system tetrahydronaphthalene/poly(ethylene oxide)/oligo(dimethyl siloxane‐b‐ethylene oxide) using a rheo‐optical device and in the case of Tl/s additionally a viscometer. This system enables for the first time a joint investigation of both transitions with a given mixture. Shear favors the homogeneous liquid state and the formation of crystals. Tcp (liquid/liquid demixing, UCST) shifts to lower and Tl/s (liquid/solid, segregation of PEO) to higher temperatures by several degrees as the shear rate,$\dot \gamma$, is increased up to 500 s−1. The normalized shift in Tcp fits well into previous results for high molecular weight blends, oligomer mixtures, polymer solutions in single solvents and low molecular weight mixtures. A phase separated near critical blend was examined 1 K below its Tcp by means of a shear cell (Linkam) in the quiescent state and under shear with respect to its morphology. Upon an increase in $\dot \gamma$one observes a transition from the co‐continuous structures existing in the quiescent state via deformed and oriented particles to string like morphologies. Finally, at sufficiently high shear rates the mixture becomes homogeneous and structures can no longer be seen under the microscope. The morphologies developing after the secession of shear are pointing to pronounced influences of the flow history of the system on the final structure of two phase blends.Equilibrium phase diagram of the system THN/COP/PEO at the indicated temperatures as obtained from turbidimetric titration. The curve for 42 °C indicates the compositions under which the mixtures segregate the first solid PEO particles upon cooling. The curves for the higher temperatures denote the demixing of the homogeneous system into two liquid phases.imageEquilibrium phase diagram of the system THN/COP/PEO at the indicated temperatures as obtained from turbidimetric titration. The curve for 42 °C indicates the compositions under which the mixtures segregate the first solid PEO particles upon cooling. The curves for the higher temperatures denote the demixing of the homogeneous system into two liquid phases.
Free Radical Polymerization of Styrene with a New Tetrafunctional Peroxide Initiator
Authors: Fityani‐Trimm Sabile , Dhib Ramdhane , Penlidis Alexander 
Published: June 2004

AbstractBulk, free‐radical polymerization of styrene was carried out in the presence of a new tetrafunctional initiator (JWEB50, ATOFINA Chemicals, Inc.). The objective was to investigate the effect of initiator functionality on the free radical polymerization process. Size exclusion chromatography (SEC) with an on‐line multi‐angle laser light scattering (MALLS) detector was used to measure molecular weight (MW), molecular weight distribution (MWD), and radius of gyration (Rg) of polystyrene. These results were compared to those with a monofunctional initiator, LupTBEC, also from ATOFINA. At equivalent molar concentrations, initiation with JWEB50 and LupTBEC produced polystyrene with similar MWs and MWDs. However, the rate of polymerization was faster with JWEB50. When LupTBEC was four times the molar concentration of JWEB50, equal rates of polymerization were achieved for both initiators. The MWDs were again similar, but the MWs were higher for the tetrafunctional initiation. Degree of branching and gelation were also investigated. A mixture of branched and linear polymer was produced by JWEB50, while no insoluble gel was formed.
Decomposition of JWEB50, a tetrafunctional initiator.imageDecomposition of JWEB50, a tetrafunctional initiator.
Preparation and Electrorheological Characterization of Suspensions of Monodisperse Micron‐Sized Styrene–Acrylonitrile Copolymer Particles
Authors: Jun Jung‐Bae , Uhm Seong‐Yong , Suh Kyung‐Do 
Published: June 2004

AbstractMonodisperse micron‐sized styrene–acrylonitrile copolymer (SAN) particles were prepared by a seeded swelling and polymerization method. Polystyrene particles prepared by dispersion polymerization were used as the seed latex. Characteristics of the particles were examined by scanning electron microscopy, FT‐IR spectroscopy, 1H NMR spectroscopy, thermogravimetric analysis and dielectric analysis, then the electrorheological (ER) behavior of the particle suspensions in silicone oil was investigated. The polarization ability of particles represented by the particle dipole coefficient increased greatly with the degree of hydrolysis of the nitrile component of SAN particles. As the acrylonitrile content of the copolymer particles was increased, the hydrolyzed particles exhibited higher dipole coefficients and, consequently, increased ER properties. Also, the effect of particle size on ER properties was studied by varying the size of these monodisperse copolymer particles.
SEM photographs of nonhydrolyzed SAN50 microspheres (a) and the corresponding hydrolyzed SAN50 microspheres (b).imageSEM photographs of nonhydrolyzed SAN50 microspheres (a) and the corresponding hydrolyzed SAN50 microspheres (b).
The Influence of Hydrogen Bonding on the Propagation Rate Coefficient in Free‐Radical Polymerizations of Hydroxypropyl Methacrylate
Authors: Beuermann Sabine , Nelke Dorit 
Published: June 2004

AbstractThe propagation rate coefficient kp was determined for hydroxypropyl methacrylate by applying pulsed laser initiated polymerizations and subsequent analysis of the polymer by size‐exclusion chromatography. kp data were derived for polymerizations in bulk and in several solvents: toluene, tetrahydrofuran (THF), benzyl alcohol, and supercritical CO2. With the exception of THF, no solvent influence on kp was observed. For polymerizations in THF kp values 40% below the corresponding bulk data were obtained. In addition, the activation energy of kp for polymerizations in THF is higher than for the other systems. The results are explained by a complexation of the OH group contained in the ester group with THF. As a consequence, H bonds between OH groups and carbonyl O atoms, which occur in the other systems, are not formed in the presence of THF. This explanation is supported by Raman spectra, which show that association of carbonyl groups does not occur for systems containing THF, whereas for all other systems the occurrence of two peaks at 1 703 cm−1 and 1 720 cm−1 is indicative of the vibrations of two different – associated vs. not associated – types of carbonyl groups. Based on the change in activation energy it is suggested that a true kinetic solvent effect occurs.
Temperature dependence of kp for HPMA polymerizations in bulk and in solution of THF. The literature data for bulk polymerizations are taken from ref. 22. Open symbols refer to νrep = 10 Hz and filled symbols to νrep = 25 Hz.imageTemperature dependence of kp for HPMA polymerizations in bulk and in solution of THF. The literature data for bulk polymerizations are taken from ref. 22. Open symbols refer to νrep = 10 Hz and filled symbols to νrep = 25 Hz.
Amination of Poly(ether imide) Membranes Using Di‐ and Multivalent Amines
Authors: Albrecht Wolfgang , Seifert Barbara , Weigel Thomas , Schossig Michael , Holländer Andreas , Groth Thomas , Hilke Roland 
Published: June 2004

AbstractCovalently aminated polyimide membranes are prepared by wet chemistry using different amines as modifiers. During this synthesis process carbonyl groups of the imide ring react with amine groups forming amide groups maintaining the macromolecular structure and an additional amide group bearing free amine groups. The reaction sequence was verified by FTIR‐ATR and XPS measurements. Using poly(ethylene imine)s, highly aminated polyimide membranes with amine contents higher than 500 nmol/cm2 membrane can be produced which can be used as basic functions for further modification. As a result of amination, the hydrophobic polyimide membranes were strongly hydrophilized. Depending on the process parameters for functionalization and the applied modifier, a symmetric or an asymmetric distribution of amine functions across the membrane was observed. The distributions of amine functions were determined by SEM microscopy (EDX mode) and by AR‐XPS (take‐off angle resolved XPS). Calculations suggest that in the case of an asymmetric distribution the pores of the surface layer are almost completely filled with a swollen network of the modifier, which allows the covalent binding of second modifiers in order to obtain new types of composite membranes.
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Kinetic Studies of the Copolymerization of Ethylene with Norbornene by ansa‐Zirconocene/Methylaluminoxane Catalysts: Evidence of a Long‐Lasting “Quasi‐Living” Initial Period
Authors: Jansen Johannes Carolus , Mendichi Raniero , Sacchi Maria Carmela , Tritto Incoronata 
Published: June 2004

AbstractCopolymers of ethylene (E) with norbornene (N) were synthesized using the catalysts rac‐Et(Ind)2ZrCl2/MAO (1), 90%rac/10%meso‐Et(4,7‐Me2Ind)2ZrCl2/MAO (2), and rac‐H2C(3‐t‐BuInd)2ZrCl2/MAO (3). Catalyst activity, molar mass (MM), and copolymer composition were studied as a function of time. The polymers showed an unusually narrow molar mass distribution (MMD) and a significant increase of their MM with time for up to one hour, suggesting a “quasi‐living” polymerization at 30 °C. The experimental data were fitted to kinetic equations and the propagation and transfer reactions were described in quantitative terms. Norbornene greatly depressed the propagation rate, along with the chain transfer rate. The more sterically hindered catalysts of the series showed lower propagation and chain transfer turnover frequency than 1 and yielded polymers with a low (2) to very low (3) norbornene content. The presence of norbornene in solution seemed to be one of the main factors responsible for the observed “quasi‐living” character of the copolymerization, probably due to coordination of norbornene to the active site. Time‐resolved kinetic studies also allowed for the calculation of the fraction of active metal centers, ranging from 56% (3) and 66–68% (1) to 94% (2) of the total zirconium present, depending on catalyst structure.
Left: molar mass (top) and polydispersity (bottom) as a function of the normalized polymer yield. The dashed line is the theoretical curve for ideal living polymerization. Catalysts 1 (□), 2 (▵), and 3 (○) at N/E ratio 12.5 and catalyst 1 (⋄) at N/E ratio 28.4. Right: enlargement of the low yield section.imageLeft: molar mass (top) and polydispersity (bottom) as a function of the normalized polymer yield. The dashed line is the theoretical curve for ideal living polymerization. Catalysts 1 (□), 2 (▵), and 3 (○) at N/E ratio 12.5 and catalyst 1 (⋄) at N/E ratio 28.4. Right: enlargement of the low yield section.
A New Class of Cationic Organoiron Polynorbornenes Containing Azo Dyes
Authors: Abd‐El‐Aziz Alaa S. , Okasha Rawda M. , Afifi Tarek H. , Todd Erin K. 
Published: June 2004

AbstractRing‐opening metathesis polymerization of novel organoiron norbornene monomers functionalized with azobenzene chromophores using the Grubbs catalyst resulted in the production of the corresponding cationic organoiron polynorbornenes. UV‐vis analysis of the organometallic polymers in DMF showed maxima from 420–430 nm, and upon acidification a bathochromic shift to 510–520 nm was observed. Cyclic voltammetric studies showed that the iron centers underwent reversible reduction steps between −1.2 and −1.4 V. Thermogravimetric analysis of the organoiron polymers showed two weight loss steps from 225 to 255 °C and from 400 to 510 °C. Differential scanning calorimetry showed that the cationic organoiron polynorbornenes had glass transition temperatures (Tg) between 145 and 178 °C, while the Tg values of their organic analogs occurred between 99 and 104 °C.
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Stable Free‐Radical Polymerization of Styrene in Combination with 2‐Vinylnaphthalene Initiation
Authors: Lizotte Jeremy R. , Long Timothy E. 
Published: June 2004

AbstractThe elevated temperatures required for the stable free‐radical polymerization (SFRP) process lead to thermal initiation of styrene via the classic Mayo mechanism. Studies have shown the utility of styrene thermal initiation in controlled autopolymerization processes. In addition, the thermal polymerization of 2‐vinylnaphthalene (2VN), a styrenic derivative with an additional fused ring, was examined. An Arrhenius analysis of the 2VN thermal polymerization process using in‐situ FT‐IR spectroscopy demonstrated a greater propensity for 2VN thermal polymerization compared to styrene. A modified Mayo mechanism was proposed based on additional resonance stabilization in 2VN derived radicals compared to a single ring of resonance stabilization for styrene. The utility of 2VN as an initiator in the SFRP of styrene was investigated. 2VN initiation resulted in polymers that are end‐functionalized with a single 2VN unit or a polycyclic unit that results from Diels‐Alder reaction in the initiation mechanism. Variation of the styrene/2VN molar ratio in the presence of 2,2,6,6‐tetramethylpiperdinyl‐1‐oxyl enabled molecular weight control and narrow molecular weight distributions (ca. 1.1–1.2). The integrity of the polymer end groups was confirmed using 1H NMR and UV‐vis spectroscopy. In addition, the UV‐vis absorbance of the 2VN initiating unit was used for construction of a calibration curve for molecular weight prediction based on the intensity of the absorbance at 312 nm associated with 2VN initiation. The observed rate constant for the polymerization initiated with 2VN (1.73 × 10−5 s−1) was comparable to that of benzoyl peroxide (kobs = 1.99 × 10−5 s−1) initiation.
SFRP of styrene thermally initiated with 2VN.imageSFRP of styrene thermally initiated with 2VN.
Interconversion of Alternating Poly(ester amide)s and Cyclic Ester Amides from Adipic Anhydride and α,ω‐Amino Alcohols
Authors: Fey Thomas , Keul Helmut , Höcker Hartwig 
Published: June 2004

AbstractPoly(esters amide)s from adipic anhydride and α,ω‐amino alcohols were obtained by polycondensation of α‐carboxyl‐ω‐hydroxyl amides under mild conditions in solution or by bulk polycondensation at elevated temperatures. For the polycondensation in bulk the influence of catalyst and of temperature on the number‐average molecular weight was studied. At a temperature of 170 °C the polycondensation process is followed by a ring‐closing depolymerisation and the formation of cyclic ester amides. Ten‐ to fourteen‐membered cyclic ester amides were obtained and characterized. The ring‐opening polymerisation of these cyclic ester amides leads, in a controlled mode, to poly(ester amide)s. The interconversion of poly(ester amide)s and cyclic ester amides by ring‐closing depolymerisation and ring‐opening polymerisation is possible. The poly(ester amide)s from adipic anhydride and homologous α,ω‐amino alcohols H2N(CH2)xOH (x = 2–6) are semicrystalline materials, their melting points show the odd/even effect observed for [n]‐polyamides and [n]‐polyurethanes.
Synthesis of alternating poly(ester amide)s.imageSynthesis of alternating poly(ester amide)s.
Photocontrol of Birefringence and In‐Plane Molecular Orientation in Copolymer Liquid Crystal Films with 4‐Methoxyazobenzene and Photo‐Cross‐Linkable Side Groups
Authors: Kawatsuki Nobuhiro , Uchida Emi , Yamamoto Tohei 
Published: June 2004

AbstractControl of the in‐plane orientation direction in a polymethacrylate copolymer liquid crystal film substituted with 4‐methoxyazobenzene (4MAz) and 4‐methoxycinnamoyloxybiphenyl (4MCB) side groups, and control of the reversible birefringence of the resultant oriented film are described. High‐order in‐plane molecular orientation was generated by irradiating with linearly polarized (LP) 365 nm light and subsequent annealing. By adjusting the exposure dose, the reorientation direction was controlled parallel and perpendicular to the electric vector (E) of the LP light. Cooperative reversion of the orientation direction for both the 4MAz and 4MCB groups was observed, and the orientational order, S, varied from −0.79 to +0.75, without the side groups aggregating. The degree of the photoreaction and the distribution of the photoproducts from the 4MAz and 4MCB side groups through the axis‐selective photoreaction explain the reversion of the orientation direction. Optical recording, erasing, and birefringent control of the resultant oriented films were demonstrated by employing the photoisomerization of the 4MAz side groups using nonpolarised (NP) 405 nm light.Order parameters of a P1 film after irradiating with LP 365 nm light (circles) and that following subsequent annealing (squares), as a function of exposure energy.imageOrder parameters of a P1 film after irradiating with LP 365 nm light (circles) and that following subsequent annealing (squares), as a function of exposure energy.
Shear Induced Demixing and Rheological Behavior of Aqueous Solutions of Poly(N‐isopropylacrylamide)
Authors: Badiger Manohar V. , Wolf Bernhard A. 
Published: June 2004

AbstractThe interrelation between the phase separation behavior and the rheological performance of aqueous solutions of high molecular weight (Mw = 1 600 kg/mol) poly(N‐isopropylacrylamide) was investigated. The system demixes upon heating and the cloud point temperature, Tcp decreases steadily with rising polymer concentration up to 10 wt.‐%. The application of shear supports phase separation and reduces Tcp markedly. This observation is interpreted in terms of destruction of intersegmental clusters formed in the quiescent state owing to favorable interactions. Intrinsic viscosities and Huggins coefficients as well as the viscosities, η at higher polymer concentrations are closely connected with the thermodynamic conditions. [η] decreases by almost two orders of magnitude upon heating, whereas the corresponding increase of kH is less pronounced. The η values (constant shear rate) of the moderately concentrated solutions as function of T pass a maximum at the corresponding phase separation temperatures. The existence of clusters also manifests in terms of stress overshoot and of particularities observed with solutions that are sheared for the first time.
Transmittance (ratio of intensities of the transmitted light and the incidence light) of a 2.0 wt.‐% PNIPAm solution in water as a function of temperature at different shear rates indicated. Heating rate is 0.22 °C/min.imageTransmittance (ratio of intensities of the transmitted light and the incidence light) of a 2.0 wt.‐% PNIPAm solution in water as a function of temperature at different shear rates indicated. Heating rate is 0.22 °C/min.
A Suitable Photoinitiator for Pulsed Laser‐Induced Free‐Radical Polymerization
Authors: Buback Michael , Kuelpmann Albrecht 
Published: June 2004

AbstractDetailed kinetic studies into free‐radical polymerization via pulsed laser experiments ideally require photoinitiators which almost instantaneously dissociate into primary free‐radical fragments that rapidly add to monomer molecules and thus induce macromolecular growth. 2‐Methyl‐4′‐(methylthio)‐2‐morpholinopropiophenone (MMMP) is shown to be such a suitable photoinitiator. Measurement of monomer conversion induced by a single laser pulse, within the so‐called single‐pulse pulsed laser polymerization (SP–PLP) experiment, provides direct information about the chain‐length dependence of the termination rate coefficient if MMMP is used as the photoinitiator.Relative monomer concentration vs time trace of a methyl acrylate homopolymerization at 40 °C and 2 000 bar where MMMP was used as the initiator. The primary radical concentration from MMMP photo‐decomposition increases from curve (a) to (b) to (c) by the ratios 1:2.2:5.7.imageRelative monomer concentration vs time trace of a methyl acrylate homopolymerization at 40 °C and 2 000 bar where MMMP was used as the initiator. The primary radical concentration from MMMP photo‐decomposition increases from curve (a) to (b) to (c) by the ratios 1:2.2:5.7.
Early Stages of Propylene Bulk Phase Polymerization with Supported Metallocene Catalysts
Authors: Knoke Stefan , Korber Frank , Fink Gerhard , Tesche Bernd 
Published: June 2004

AbstractFor the initial steps of propylene bulk phase polymerization with a silica‐supported metallocene/MAO‐catalyst the processes of polymer growth, particle expansion and carrier fragmentation are investigated. Gravimetric analysis of the kinetics is given. Light optical examination of the particles shows a significant particle expansion during the first minutes of polymerization, which is not comparable to known observation from the slurry process. Electron microscopic investigation on cross sections of the polymer particles allows a detailed insight into the process of polymer growth, carrier fragmentation and particle expansion. The results are compared with the polymer growth and particle expansion model developed with slurry polymerizations under mild model conditions. In bulk phase polymerization particle expansion and carrier fragmentation are much faster due to more drastic reaction conditions. Nevertheless, it is still possible to observe a shell‐by‐shell degradation of the carrier material. Varying start up behaviors of single catalyst grains are observed. We are able to correlate the initial polymerization activity of individual grains with the cocatalyst loading and distribution on the catalyst carrier by means of microanalytical techniques. The results explain the varying start up behaviors of single grains. It becomes clear why different states of fragmentation are mixed up in the observed polymer samples.Insight into catalyst grains after 0.5 min propylene bulk phase polymerization.imageInsight into catalyst grains after 0.5 min propylene bulk phase polymerization.