bluuebunny/crossref_metadata_2025 huggingface dataset:
Molecular Weight Development during Simultaneous Chain Scission, Long‐Chain Branching and Crosslinking, 2
Authors: Tobita Hidetaka
Published: March 2003

The matrix formula developed in Part 1 of this series is applied to describe the molecular weight development during free‐radical (co)polymerization. All of the required probabilistic parameters are expressed in terms of the kinetic rate constants and pertinent concentrations. In free‐radical polymerization, the primary chains are formed consecutively. The segments that constitute nonlinear polymer molecules are divided into N fractions on the basis of the birth conversion levels, and the weight‐average molecular weight of the whole reaction system is obtained by extrapolating N to infinity. Practically, such extrapolation can be conducted by using the calculated values for only three different N values with sufficient accuracy. In the context of the present theory, not only the full molecular weight distribution but also the polymer structure formed can be determined directly by using the Monte Carlo simulation method.

Calculated weight‐average chain length development.

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Calculated weight‐average chain length development.
Model Reduction in Emulsion Polymerization Using Hybrid First‐Principles/Artificial Neural Network Models
Authors: d'Anjou Alicia , Torrealdea F. Javier , Leiza José R. , Asua José M. , Arzamendi Gurutze
Published: March 2003

A first‐principles mathematical model for emulsion polymerization was reduced by using a hybrid mathematical model composed by artificial neural networks (ANN) and material balances. The goal was to have an accurate model that may be integrated fast enough to be used for online optimization purposes. In the reduced model the polymerization rate and the instantaneous weight‐average molecular weight were calculated by means of artificial neural networks. These ANNs were incorporated to first‐principles material balances. The accuracy of the reduced model under a wide range of conditions was assessed. Savings in computer time were achieved by using the reduced model, which makes it suitable for online optimization purposes.

Effect of the temperature on the cumulative weight‐average molecular weight: first principles mathematical model (—); $\overline {{\rm M}_{{\rm w},{\rm inst}} }$(ANN2) and hybrid model predictions: (▵) 50 °C, (▪) 60 °C(training), (▿) 70 °C(validation), (•) 80 °C, (○) 90 °C.

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Effect of the temperature on the cumulative weight‐average molecular weight: first principles mathematical model (—); $\overline {{\rm M}_{{\rm w},{\rm inst}} }$(ANN2) and hybrid model predictions: (▵) 50 °C, (▪) 60 °C(training), (▿) 70 °C(validation), (•) 80 °C, (○) 90 °C.
RIS Models and Unperturbed Chain Properties of Polyesters Containing 1,3‐Cyclobutylene and 1,4‐Cyclohexylene Linkages
Authors: Sulatha Muralidharan S. , Natarajan Upendra
Published: March 2003

Polyesters containing 1,3‐cyclobutylene and 1,4‐cyclohexylene linkages in the main chain are investigated using conformational energy calculations. Rotational isomeric state (RIS) models are developed for poly(1,4‐cyclohexylenedimethylene terephthalate) (PCT), poly(1,4‐cyclohexylenedimethylene 2,5‐dimethylterephthalate) (DMPCT), poly(1,4‐cyclohexylenedimethylene 1,4‐cyclohexylenedicarboxylate) (PCC), and poly(2,2,4,4‐tetramethyl‐1,3‐cyclobutylene terephthalate) (CBDO). In DMPCT, the ester linkage prefers skewed conformations with respect to the phenyl group to relieve the steric strain caused by the methyl groups. The methyl groups on the cyclobutanediol moiety in CBDO restrict the rotational freedom about the oxycyclobutylene linkage. The unperturbed dimensions as described by characteristic ratio and persistence length are calculated for the trans and cis configurations of these polyesters. CBDO shows highly extended chain conformations among these polyesters indicating relative chain rigidity of the backbone. For DMPCT and PCC, in their trans configuration, the chain dimensions decrease with an increase in temperature while for their cis configurations, the chain dimensions increase with temperature, arising from basic differences in the fragment structures that control the competition of the relative populations as affected by temperature. Temperature has negligible influence on the unperturbed dimensions of both isomeric linkages of CBDO, while this is true for the trans configuration of PCT. The study shows that induction of cyclobutylene groups in the main chain results in a greater rigidity for homopolyesters than for chains with cyclohexylene groups.

Structure of the repeat units of polyesters in the planar trans configuration and the schematic of the RIS models with definition of geometrical parameters.

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Structure of the repeat units of polyesters in the planar trans configuration and the schematic of the RIS models with definition of geometrical parameters.
Organische Polymere als funktionelle Werkstoffe für chemische Sensoren
Authors: Kaden H. , Berthold M. , Jahn H.
Published: March 2003

Die Funktion vieler chemischer Sensoren für Messungen in Flüssigkeiten und in Gasen bei Umgebungstemperatur beruht auf der Kombination eines Transducers mit organischen Membranen. Diese Membranen bestimmen wesentliche Sensoreigenschaften wie Selektivität und Ansprechverhalten. Außerdem schützen sie das Detektionssystem vor äußeren Einflüssen.

Die Auswahl und Entwicklung von Polymermembranen ist deswegen ein wesentlicher Bestandteil der Sensorforschung und ‐entwicklung. Dabei sind elektrische, optische und biologische Eigenschaften der Polymere von Bedeutung. Es wird eine Übersicht über die in der Sensorik eingesetzten Materialien gegeben.

Von besonderem Interesse für die Sensorforschung sind in letzter Zeit intrinsisch leitende Polymere (ILP), deren Eigenschaften neue Möglichkeiten der Sensorentwicklung eröffnet haben. Am Beispiel einer elektrochemischen pH‐Glaselektrode mit innerer Feststoffableitung wird gezeigt, dass Polypyrrol als Material für eine langzeitbeständige Potentialableitung und damit als Ersatz bisher ausschließlich verwendeter sog. elektrochemischer Elektroden 2. Art dienen kann. Praxiserprobungen bestätigen die Eignung dieses Polymermaterials. Aspekte des Transportmechanismus elektrischer Ladungen über die Grenzfläche ILP | Glas werden diskutiert.
Lenzing LYOCELL: Potentiale und Chancen einer neuen Fasergeneration
Authors: Harms H.
Published: March 2003

Cellulose ist der wichtigste „organische Konstruktions‐ und Funktionswerkstoff”︁ der Natur und weist dementspechend eine umfassenden Palette hervorragender und sehr spezifischer Eigenschaften auf. Diese Eigenschaften können für verschiedenste Produkte zugänglich gemacht und auch gezielt modifiziert werden, sobald es einem gelingt, die Cellulose in Lösung zu bringen und dann in der gewünschten Form auf geeignete Weise zu regenerieren.

Die fortschreitende Entwicklung der neuen Lyocellfaser, das zunehmende Wissen um ihre Leistungsfähigkeit und die Möglichkeiten sie zu modifizieren, aber auch eine Reihe völlig „neuer Anwendungen”︁ des Lyocell Verfahrens für andere Produkte zeigen, daß die direkte Regeneration der Cellulose aus organischer Lösung eine völlig neue Nutzung ihres hervorragenden Eigenschaftspotentials ermöglicht. Lyocell öffnet also nicht nur die Chance für eine neue Generation cellulosischer Fasern ‐ auch für neue Einsatzgebiete ‐ sondern auch für eine Renaissance der Cellulose für unterschiedliche Produkte, bei denen sie einerseits in den letzten Jahrzehnten durch vollsynthetische Polymere substituiert wurde und bei denen andererseits völlig neue Anwendungen für dieses hervorragende Polymer erschlossen werden.
ABOUT THE CHARACTERIZATION OF THE MECHANICAL PROPERTIES OF NATURAL FIBRES
Authors: MIECK K.‐P. , REUSSMANN, T. , NECHWATAL A.
Published: March 2003

All composite models contain the E‐modulus or the tenacity of the reinforcing fibres. Therefore the exact measurement of the fibre properties is the essential prerequisite to achieve an agreement between the theoretical approaches and the practical results. Here some special problems in the fibre testing of natural fibres are discussed.
Chemische Zusammensetzung und Mikrostruktur polymerabgeleiteter Gläser und Keramiken im System Si–C–O. Teil 2: Charakterisierung der Gefügeausbildung mittels hochauflösender Durchstrahlungselektronenmikroskopie und Feinbereichsbeugung
Authors: Gegner J.
Published: March 2003

Flüssige oder feste Siliconharze bilden die wirtschaftlich interessanteste Gruppe organischer Vorstufen zur pyrolytischen Herstellung von Glas‐ und Keramikwerkstoffen auf Siliziumbasis. Da dichte, maßstabile Bauteile kostengünstig durch Beimischung reaktiver Füllstoffpulver erreicht werden können, müssen chemische Zusammensetzung und Gefügeentwicklung der polymerabgeleiteten Rückstände während der thermischen Zersetzung genau bekannt sein. In der vorliegenden Arbeit werden deshalb die durch Pyrolyse des Modellprekursors Polymethylsiloxan bei Temperaturen von 525 bis 1550 °C hergestellten Gläser und Keramiken untersucht. Mittels analytischer Elektronenmikroskopie wurde in Teil 1 der Bindungszustand von Silizium im Nanometerbereich bestimmt und die Phasentrennung der metastabilen Si–C–O‐Matrix in SiO2, C und SiC nachgewiesen. Die in‐situ‐Kristallisation konnte durch Zugabe feinkörniger Pulver inerter Füllstoffe, wie Al2O3 oder SiC, wesentlich beschleunigt werden, was eine wirksame Prozesssteuerung ermöglicht. In Teil 2 wird die Mikrostruktur mittels hochauflösender Durchstrahlungselektronenmikroskopie und Feinbereichsbeugung charakterisiert. Es scheiden sich turbostratischer Kohlenstoff und kubisches β‐SiC als Kristallisationsprodukte aus. Diese Phasen sind in eine amorphe Matrix eingebettet. Inerte Füllstoffe senken die Kristallisationstemperatur um mehrere hundert °C. In diesem Fall wirkt das polymerabgeleitete Si–C–O‐Material als Bindemittel zwischen den Pulverteilchen. Reaktionsschichtbildung findet nicht statt. Bei den untersuchten Pyrolysebedingungen wurde keine Kristallisation von SiO2 beobachtet.
Planar waveguide add/drop wavelength filters based on segmented gratings
Authors: Tomljenovic‐Hanic S. , Love J. D.
Published: March 2003

We investigate the application of segmented reflection gratings in planar devices that can function as either a single‐ or two‐wavelength add/drop filter. The role of the segmented gratings is analogous to that of a blazed grating, but can provide a higher reflectivity level at the Bragg wavelength, eliminate back reflection into the fundamental mode, and provide arbitrarily close channel spacing in the two‐wavelength case. © 2003 Wiley Periodicals, Inc. Microwave Opt Technol Lett 37: 163–165, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.10855
A wideband rectangular patch antenna with shorting pins
Authors: Chair R. , Mok W. C. , Luk K. M. , Lee K. F.
Published: March 2003

This paper presents a novel bandwidth enhancement technique by using shorting pins. A low‐profile rectangular‐shaped patch antenna with three shorting pins is presented. The impedance bandwidth of the proposed antenna achieves 33% (SWR < 2) while the overall thickness of the antenna is only 0.06λ0. The antenna has two close resonant bands. The lower resonant band has a conical radiation pattern with 4‐dBi maximum gain and the higher resonant band has a broadside radiation pattern with 8‐dBi maximum gain. © 2003 Wiley Periodicals, Inc. Microwave Opt Technol Lett 37: 165–167, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.10856
Fast calculation of the propagation constants of leaky and Berenger modes of planar and circular dielectric waveguides terminated by a perfectly matched layer
Authors: Rogier Hendrik , Knockaert Luc , De Zutter Daniël
Published: March 2003

A fast technique is proposed to determine the complex propagation constants of the leaky and Berenger modes of circular dielectric waveguides terminated by a perfectly matched layer (PML). The method relies on a coordinate transformation in the complex plane and uses the approximate analytical solutions of the dispersion relations as a first estimate. The efficiency of the technique is shown for a microstrip substrate and a VCSEL configuration, both terminated by a perfectly matched layer. © 2003 Wiley Periodicals, Inc. Microwave Opt Technol Lett 37: 167–171, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.10857
Photonics true‐time delay using a tunable‐fiber laser source based on a high‐birefringence fiber‐loop‐mirror filter
Authors: Yang Jianliang , Tjin Swee Chuan , Ngo Nam Quoc
Published: March 2003

A photonics true‐time‐delay (TDD) system using a chirped grating and a novel fiber‐ring laser is proposed and demonstrated. A high‐birefringence fiber‐loop mirror (HiBi‐FLM) is integrated in the laser cavity to act as a polarization‐independent wavelength filter. By properly adjusting the polarization controllers in the HiBi‐FLM, desirable lasing wavelength and number or wavelength spacing can be achieved. © 2003 Wiley Periodicals, Inc. Microwave Opt Technol Lett 37: 171–174, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.10858
A wideband arrowhead planar monopole antenna for multi‐service mobile systems
Authors: Cabedo‐Fabrés M. , Nogueira Alejandro Valero , Bataller Miguel Ferrando
Published: March 2003

A compact wideband arrowhead planar monopole antenna is obtained by trimming the lower edges of the triangular planar monopole. The shorted arrowhead monopole is very suitable for use in multi‐service wireless systems, yielding a measured bandwidth of 5:1 for VSWR < 2.1 while retaining good radiation characteristics. © 2003 Wiley Periodicals, Inc. Microwave Opt Technol Lett 37: 188–190, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.10863
Experimental investigation of the performance of co‐ and counter‐pumped Raman fiber amplifiers
Authors: Xiangjun Xin , Chongxiu Yu , Jianhua Ren , Anjian Li , Qiang Wu , Yu Xin , Chuanlin Wang , Wenxiao Zheng , Shuangchen Ruan , Geguo Du , Xiaoqiang Yang , Gang Xin
Published: March 2003

Gain, gain saturation, optical signal‐to‐noise ratio (OSNR), and pump power conversion efficiency (PCE) of co‐ and counter‐pumped Raman fiber amplifiers (RFAs) are investigated and compared experimentally in this paper. Results show that obvious OSNR improvement can be achieved with co‐pumped RFAs. Compared with the counter‐pumped scheme, the co‐pumped solution has more severe gain saturation. PCE decreases as the input power increases for both pumping schemes, however, PCE decreases faster for the co‐pumped RFAs. © 2003 Wiley Periodicals, Inc. Microwave Opt Technol Lett 37: 190–194, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.10864
Low‐pass impedance matching filters for packaged low‐cost laser diodes
Authors: Music H. , Alping A. , Johansson U. , Hedquist T. , Gevorgian Spartak
Published: March 2003

A simple, cost‐effective, and compact passive matching network, in the form of a low‐pass filter, is developed for impedance matching of a commercially packaged laser diode with an optical connector. More than 15‐dB matching improvement is achieved at 1.8‐GHz frequency by using a small size (10.8 × 9.1 mm) three‐pole lumped element low‐pass LC filter. © 2003 Wiley Periodicals, Inc. Microwave Opt Technol Lett 37: 194–196, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.10865
Angular spread at 2.1 GHz while entering tunnels
Authors: García‐Pardo José María Molina , Rodríguez José Victor Rodríguez , Juan‐Llácer Leandro
Published: March 2003

Propagation characteristics while entering tunnels are analyzed by using a ray‐launching technique and the uniform theory of diffraction (UTD). RMS angular spread is studied and related to the “excitation zone.” This paper presents interesting differences in the behavior of this parameter and the RMS delay spread. © 2003 Wiley Periodicals, Inc. Microwave Opt Technol Lett 37: 196–198, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.10866
Assessment of the GA‐based adaptive array control strategy: The case of stochastic life‐time co‐channel interferences
Authors: Donelli Massimo , Lommi Andrea , Massa Andrea , Sacchi Claudio
Published: March 2003

In this paper, the performances of an adaptive antenna array control strategy, based on an improved genetic algorithm, are evaluated in terms of signal‐to‐interference‐noise ratio (SINR). The working case considered deals with the presence of co‐channel interfering signals characterized by stochastic arrivals, phases, and lifetime. This scenario provides a reliable testing benchmark for such array control methodologies. The simulation results prove the robustness of the learned real‐time genetic algorithm (LRTGA) in the presence of non‐deterministic interferences as well. © 2003 Wiley Periodicals, Inc. Microwave Opt Technol Lett 37: 198–201, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.10867
A new type of slow‐wave 1D PBG microstrip band‐pass filter
Authors: Nesic Dusan
Published: March 2003

In this paper, a new type of slow‐wave 1D PBG microstrip band‐pass filter with a half‐wavelength linear resonator is introduced. Reduction of the central frequency (slow‐wave effect) is over 50%, as compared to the conventional band‐pass filter of the same type. Additional coupling is over tuning narrow lines that can be used to regulate the filter's performance. In addition, it has very good S11 parameters and low losses in the band‐pass. Simulation and experimental results are in good agreement. © 2003 Wiley Periodicals, Inc. Microwave Opt Technol Lett 37: 201–203, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.10868
Lumped impedance matching using a hybrid genetic algorithm
Authors: du Plessis W. P. , Abrie P. L. D.
Published: March 2003

A new impedance matching algorithm based on a hybrid genetic algorithm is presented. Unlike real‐frequency techniques, this new algorithm does not require ideal transformers, resonant sections are allowed, component ranges can be specified, and parasitic effects can be included. The results obtained are comparable to those obtained with the best published techniques. © 2003 Wiley Periodicals, Inc. Microwave Opt Technol Lett 37: 210–212, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.10871
The effect of IP traffic burstiness on four‐wave mixing crosstalk in WDM networks
Authors: Tang Junhua , Zhang Liren , Siew Chee‐Kheong
Published: March 2003

The effect of bursty IP traffic on the statistics of four‐wave mixing in wavelength division multiplexing (WDM) networks is studied in terms of the distribution of the actual four‐wave mixing power under different IP traffic conditions. A novel approach for estimating the average four‐wave mixing power in WDM network with bursty IP traffic is presented. © 2003 Wiley Periodicals, Inc. Microwave Opt Technol Lett 37: 212–214, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.10872
Microwave techniques for measurement of large‐structure vibration
Authors: Pieraccini Massimiliano , Luzi Guido , Mecatti Daniele , Gusella Vittorio , Atzeni Carlo
Published: March 2003

In this paper, the authors propose continuous‐wave single‐frequency (CW‐SF) and multi‐frequency (CW‐MF) microwave techniques for measurement of large‐structure vibration. Theoretical background and experimental results of tests on a vertical steel structure, subjected both to artificial solicitation through a vibrodyne and to wind, are reported. © 2003 Wiley Periodicals, Inc. Microwave Opt Technol Lett 37: 216–218, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.10874
A robust and efficient method for obtaining the complex modes in inhomogeneously filled waveguides
Authors: Monsoriu Juan A. , Coves Angela , Gimeno Benito , Andres Miguel V. , Silvestre Enrique
Published: March 2003

In this paper, we present a computational simulation of the complex wave propagation in inhomogeneously filled waveguides with lossless and lossy dielectrics. We use a biorthonormal‐basis method as a numerical technique. The behavior of complex modes in different waveguides whose characterization with other methods involves some difficulties is analyzed. © 2003 Wiley Periodicals, Inc. Microwave Opt Technol Lett 37: 218–222, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.10875
Reducing resonant length of sidewall‐inclined slots in a rectangular waveguide
Authors: Heidari Abbas Ali , Forooraghi Keyvan , Hakkak Mohammad
Published: March 2003

In this paper, the admittance characteristics of a dielectric filled inclined slot in the narrow wall of a rectangular waveguide have been calculated. By enforcing the continuity of the tangential magnetic field through the slot aperture, an integral equation with the tangential electric field in the slot as the unknown is obtained. An entire domain method of moments (MoM) is used to solve the integral equation. Numerical results show that the slot can resonate without penetrating onto the top and bottom broad walls of the waveguide. It has also been shown that the resonant frequency (length) and the resonant conductance of the slot depend on the dielectric constant of the material filling the slot. The computed results are shown to be in good agreement with those obtained by HP‐HFSS. © 2003 Wiley Periodicals, Inc. Microwave Opt Technol Lett 37: 222–226, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.10876
A microwave differentiator
Authors: Hsue Ching‐Wen , Kuan Ming‐Chih , Peng Chia‐Mei
Published: March 2003

A wideband differentiator is implemented by using nonuniform transmission lines. To utilize the transfer function of a differentiator developed in a study of discrete signal processing (DSP), we formulate the scattering characteristics of equal‐length electrical transmission line sections in the Z domain. A uniform line shunted with a two‐section stub is obtained to emulate the transfer function of a stable second‐order recursive differentiator. A microstrip circuit is implemented to verify this novel method and experimental results are in good agreement with theoretical design parameters. © 2003 Wiley Periodicals, Inc. Microwave Opt Technol Lett 37: 226–228, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.10877
Simple modelling of DGS to design 1D‐PBG low‐pass filters
Authors: Garde Ieltxu , Yábar Miguel Javier , del Río Carlos
Published: March 2003

The use of defected ground structures (DGSs) is being intensively explored by microwave filter designers. DGSs are one possible implementation of a 1D photonic band gap (1D‐PBG), in which some defect structures are patterned on the ground plane of a microstrip circuit. In this paper, the relation between the behaviour of DGS structures and classical microwave filter design theory is established. In particular, a simple model procedure using DGS structures, based on the classical microwave filter design theory, is presented. In order to illustrate this method, two low‐pass filters are designed, fabricated, and measured. © 2003 Wiley Periodicals, Inc. Microwave Opt Technol Lett 37: 228–232, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.10878
Polymers of carbonic acid 32: Influence of catalysts on propagation and cyclization in the interfacial polycondensation of bisphenol A with diphosgene
Authors: Kricheldorf Hans R. , Schwarz Gert , Böhme Sigrid , Schultz Claus‐Ludolf
Published: March 2003

Bisphenol A was polycondensed with diphosgene in a dichloromethane/aqueous NaOH system. Temperature, time, and molar ratios of the reactants were optimized according to a previously elaborated optimization of the hydrolytic polycondensation of bisphenol A bischloroformate. Five of the following catalysts were examined: triethylamine, 4‐(N,N‐dimethylamino)pyridine (DMAP), ethyldiisopropylamine (EDPA), tetrabutylammonium hydrogen sulfate, and triethylbenzylammonium chloride (TEBA‐Cl). Triethylamine and DMAP accelerated the hydrolysis of diphosgene by formation of a hydrophilic acylammonium salt. Therefore, the molecular weights decreased with higher concentration of these tert‐amines. However, the molecular weights increased (weight‐average molecular weight up to 106) with higher concentrations of tetraalkylammonium salts because these catalysts favor chain growth in the organic phase via “naked” phenoxide ions without catalyzing the hydrolysis of diphosgene. EDPA gave poor results under all circumstances. Cyclic polycarbonates were discovered in all samples. Their fraction increased with the average molecular weight of the samples. When samples prepared with triethylamine or TEBA‐Cl were fractionated, cycles having molar masses up to 15,000 Da were detected by matrix‐assisted laser desorption/ionization time‐of‐flight mass spectroscopy. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 890–904, 2003
Effects of diamines and their fluorinated groups on the color lightness and preparation of organosoluble aromatic polyimides from 2,2‐bis[4‐(4‐amino‐2‐trifluoromethylphenoxy)phenyl]‐hexafluoropropane
Authors: Yang Chin‐Ping , Chen Ruei‐Shin , Chen Kuei‐Hung
Published: March 2003

To investigate the position and amount of the CF3 group affecting the coloration of polyimides (PIs), we prepared 2,2‐bis[4‐(4‐amino‐2‐trifluoromethylphenoxy)phenyl]hexafluoropropane (2) with four CF3 groups with 2‐chloro‐5‐nitrobenzotrifluoride and 2,2‐bis(4‐hydroxyphenol)hexafluoropropane. A series of soluble and light‐colored fluorinated PIs (5) were synthesized from 2 and various aromatic dianhydrides (3a–3f). 5a–5f had inherent viscosities ranging from 0.80 to 1.19 dL/g and were soluble in amide polar solvents and even in less polar solvents. The glass‐transition temperatures of 5 were 221–265 °C, and the 10% weight‐loss temperatures were above 493 °C. Their films had cutoff wavelengths between 343 and 390 nm, b* values (a yellowness index) ranging from 5 to 41, dielectric constants of 2.68–3.01 (1 MHz), and moisture absorptions of 0.03–0.29 wt %. In a comparison of the PI series 6–8 based on 2,2‐bis[4‐(4‐aminophenoxy)phenyl]hexafluoropropane, 2,2‐bis[4‐(4‐amino‐2‐trifluoromethylphenoxy)phenyl]propane, and 2,2‐bis[4‐(4‐aminophenoxy)phenyl]propane, we found that the CF3 group close to the imide group was more effective in lowering the color; this means that CF3 of 5, 7, and 8f was more effective than that of 6c. The color intensity of the four PI series was lowered in the following order: 5 > 7 > 6 > 8. The PI 5f, synthesized from diamine 2 and 4,4′‐hexafluoroisopropylidenediphthalic anhydride, had six CF3 groups in a repeated segment, so it exhibited the lightest color among the four series. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 922–938, 2003
Syntheses and properties of new aromatic polybenzoxazoles bearing ether and phenylethylidene or 1‐phenyl‐2,2,2‐trifluoroethylidene linkages
Authors: Hsiao Sheng‐Huei , Chen Wei‐Tsun
Published: March 2003

Two new bis(ether acyl chloride)s, 1,1‐bis[4‐(4‐chloroformylphenoxy)phenyl]‐1‐phenylethane and 1,1‐bis[4‐(4‐chloroformylphenoxy)phenyl]‐1‐phenyl‐2,2,2‐trifluoroethane, were prepared from readily available reagents. Aromatic polybenzoxazoles with both ether and phenylethylidene or 1‐phenyl‐2,2,2‐trifluoroethylidene linkages between phenylene units were obtained by a conventional two‐step procedure including the low‐temperature solution polycondensation of the bis(ether acyl chloride)s with three bis(o‐aminophenol)s, yielding poly(o‐hydroxyamide) precursors, and subsequent thermal cyclodehydration. The intermediate poly(o‐hydroxyamide)s exhibited inherent viscosities of 0.39–0.98 dL/g. All of the poly(o‐hydroxyamide)s were amorphous and soluble in polar organic solvents such as N,N‐dimethylacetamide, and most of them could afford flexible and tough films via solvent casting. The poly(o‐hydroxyamide)s exhibited glass‐transition temperatures (Tg's) of 129–194 °C and could be thermally converted into corresponding polybenzoxazoles in the solid state at temperatures higher than 300 °C. All the polybenzoxazoles were amorphous and showed an enhanced Tg but a dramatically decreased solubility with to respect to their poly(o‐hydroxyamide) precursors. They exhibited Tg's of 216–236 °C through differential scanning calorimetry and were stable up to 500 °C in nitrogen or air, with 10% weight‐loss temperatures being recorded between 538 and 562 °C in nitrogen or air. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 914–921, 2003
Modification of polycondensation of isophthalic and terephthalic acids and bisphenols with tosyl chloride/dimethylformamide/pyridine by the presence of additives
Authors: Higashi Fukuji , Shigeta Yuhko
Published: March 2003

In copolycondensation with 2,2‐bis(4‐hydroxyphenyl)propane (BPP) and bisphenols (BPs) containing various alkylidene linkages, the associative interactions between BP moieties in the resulting oligomers most likely affected the reaction. To modify the interactions to favorably control the reaction, several additives were examined in a two‐stage polycondensation of an equimolar mixture of isophthalic acid and terephthalic acid, first with BPP (50 mol %) and next with additional BPP. Of additives used, diphenylmethane of an equivalent to BPP in the preformed oligomers was most effective. The results are discussed in terms of the distributions of resulting oligomers prepared at 70% extent of reaction. Better results were obtained when the distributions showed profiles similar to the theoretical one calculated on the basis that the reactivity of the oligomers is the same independent of their chain lengths. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 970–975, 2003
Preparation of macroporous functionalized polymer beads by a multistep polymerization and their application in zirconocene catalysts for ethylene polymerization
Authors: Liu Chengbin , Tang Tao , Huang Baotong
Published: March 2003

Macroporous functionalized polymer beads of poly(4‐vinylpyridine‐co‐1,4‐divinylbenzene) [P(VPy‐co‐DVB)] were prepared by a multistep polymerization, including a polystyrene (PS) shape template by emulsifier‐free emulsion polymerization, linear PS seeds by staged template suspension polymerization, and macroporous functionalized polymer beads of P(VPy‐co‐DVB) by multistep seeded polymerization. The polymer beads, having a cellular texture, were made of many small, spherical particles. The bead size was 10–50 μm, and the pore size was 0.1–1.5 μm. The polymer beads were used as supports for zirconocene catalysts in ethylene polymerization. They were very different from traditional polymer supports. The polymer beads could be exfoliated to yield many spherical particles dispersed in the resulting polyethylene particles during ethylene polymerization. The influence of the polymer beads on the catalytic behavior of the supported catalyst and morphology of the resulting polyethylene was investigated. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 873–880, 2003
Molecular composites prepared by in situ direct synthesis of wholly aromatic rigid‐rod polyamides via the phosphorylation reaction in a dissolved nylon‐6 matrix
Authors: Idemura Satoshi , Preston Jack
Published: March 2003

Wholly aromatic rigid‐rod polyamides such as poly(p‐phenyleneterephthalamide) (PPD‐T) were synthesized in situ in a solution of nylon‐6 via the phosphorylation polycondensation method to form nanocomposites or so‐called “molecular composites.” The incorporation of PPD‐T into a nylon‐6 matrix was achieved by this approach in a more compatibilized form than that obtained by the conventional coagulation method that entails precipitation of a blend of PPD‐T and nylon‐6 in a solvent, for example, concentrated sulfuric acid. Gelation occurred during the synthesis, presumably because of the formation of interpenetrating networks accompanied by some block‐copolymer formation. The transparency and tensile properties of the resultant composite films from the rigid‐rod aromatic polyamide/nylon‐6 combination were improved over those of nylon‐6 film alone. Rainbow‐colored intense birefringence was observed for the composite films under crossed polarizers. These properties are discussed in context with the in situ synthesized rigid‐rod polyamides uniformly incorporated in nylon‐6. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 1014–1026, 2003
Method of determining the absolute molecular weight from gel permeation chromatograms for star‐shaped styrenic block copolymers
Authors: Liu I‐Chun , Tsiang Raymond Chien‐Chao
Published: March 2003

A gel permeation chromatography (GPC) calculation method has been developed to determine the absolute molecular weight of a star‐shaped styrenic block copolymer with GPC–ultraviolet/refractive index calibrated with linear polystyrene standards. To illustrate the simplicity of this method, we have synthesized nearly monodisperse, multiple‐arm model polymers either by linking living polymeric arms with multifunctional silicon halide or by oligomerizing the p‐chloromethylstyrene‐terminated polystyrene macromonomers. The good agreement between the absolute molecular weight determined with this calculation method and that actually measured with a multi‐angle laser light scattering device has corroborated the validity of the calculation method. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 976–983, 2003
Functionalization of polymeric organolithium compounds with 3,4‐epoxy‐1‐butene: Precursors for diene‐functionalized macromonomers
Authors: Quirk Roderic P. , Gomochak Deanna L. , Wesdemiotis Chrys , Arnould Mark A.
Published: March 2003

The functionalization of polymeric organolithiums (PLi) with 3,4‐epoxy‐1‐butene (EPB) in a hydrocarbon solution yielded the corresponding hydroxybutene‐functionalized polymers in high yields (>95%). Three modes of addition of PLi to EPB were observed (1,4, 3,4, and 4,3). The products and chain‐end structures were characterized by 1H NMR, 13C NMR, attached‐proton‐test 13C NMR, calculated 13C NMR chemical shifts, and matrix‐assisted laser desorption/ionization time‐of‐flight mass spectrometry (MALDI‐TOF MS). The regioselectivity of the addition depended on the PLi chain‐end structure, the reaction conditions, and the addition of lithium salts or Lewis bases. In the absence of additives, the functionalization of poly(styryl)lithium (PSli) produced equal amounts of 1,4‐, 3,4‐, and 4,3‐addition, as determined by quantitative 13C NMR analysis. The use of a low temperature (6 °C), inverse addition, the addition of triethylamine (TEA; [TEA]/[PSLi] = 20) as a Lewis base, or dienyllithium chain ends produced polymers with only the 1,4‐addition product. Mild dehydration of the hydroxybutene‐functionalized polymer with p‐toluenesulfonic acid produced the corresponding diene‐functionalized macromonomer, as shown by MALDI‐TOF MS. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 947–957, 2003
Synthesis and spectroscopic characterization of symmetrical isoprene–methyl methacrylate diblock copolymers bearing different anthracene derivatives at the junctions
Authors: Yang Jian , Lu Jianping , Winnik Mitchell A.
Published: March 2003

We describe the synthesis and characterization of 1‐(1‐anthryl)‐1‐phenylethylene (1‐An‐E) and 1‐(2‐anthryl)‐1‐phenylethylene (2‐An‐E). These species were used to end cap the living end group of polyisoprene (PI) obtained by anionic polymerization in tetrahydrofuran. The anions generated were used to initiate methyl methacrylate polymerization. In this way, we synthesized two symmetrical PI‐poly(methyl methacrylate) (PMMA) block copolymers each with a single dye at the junction. PI‐An1‐PMMA has an anthracene linked via its 1‐position. PI‐An2‐PMMA has the anthracene linked via its 2‐position. We compare the UV and fluorescence properties of the polymers to model compounds with similar chromophores. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 1225–1236, 2003
Stereocontrol during the free‐radical polymerization of methacrylamides in the presence of Lewis acids
Authors: Isobe Yutaka , Suito Yoshikatsu , Habaue Shigeki , Okamoto Yoshio
Published: March 2003

The effects of Lewis acids, that is, rare earth metal trifluoromethanesulfonates, on the free‐radical polymerization of N‐methylmethacrylamide (MMAM), N‐isopropylmethacrylamide (IPMAM), N‐tert‐butylmethacrylamide (tBMAM), N‐phenylmethacrylamide (PMAM), and methacrylamide were examined under various conditions. A catalytic amount of Yb(OSO2CF3)3 significantly affected the stereochemistry during the radical polymerization. Polymerization solvents strongly influenced the effect of the Lewis acids. Methanol was the best solvent for increasing the isotactic specificity during the polymerization of MMAM and IPMAM, whereas tetrahydrofuran was more effective for the tBMAM and PMAM polymerizations. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 1027–1033, 2003
Synthesis of comb‐type polycarbosilanes via nucleophilic substitution reactions on the main‐chain silicon atoms
Authors: Zhang Tao , Park Soo‐Young , Farmer B. L. , Interrante Leonard V.
Published: March 2003

A series of comb‐type polycarbosilanes of the type [Si(CH3)(OR)CH2]n {where R = (CH2)mR′, R′ = O‐p‐biphenylX [X = H (m = 3, 6, 8, or 11) or CN (m = 11)], and R′ = (CF2)7CF3 (m = 4)} were prepared from poly(chloromethylsilylenemethylene) by reactions with the respective hydroxy‐terminated side chains in the presence of triethylamine. The product side‐chain polymers were typically greater than 90% substituted and, for R′ = O‐p‐biphenylX derivatives, they exhibited phase transitions between 27 and 150 °C involving both crystalline and liquid‐crystalline phases. The introduction of the polar p‐CN substituent to the biphenyl mesogen resulted in a substantial increase in both the isotropization temperature and the liquid‐crystalline phase range with respect to the corresponding unsubstituted biphenyl derivative. For R = (CH2)11O‐biphenyl side chains, an analogous side‐chain liquid‐crystalline (SCLC) polysiloxane derivative of the type [Si(CH3)(O(CH2)11O‐biphenyl)O]n was prepared by means of a catalytic dehydrogenation reaction. In contrast to the polycarbosilane bearing the same side chain, this polymer did not exhibit any liquid‐crystalline phases but melted directly from a crystalline phase to an isotropic liquid at 94 °C. Similar behavior was observed for the polycarbosilane with a fluorocarbon chain, for which a single transition from a crystalline phase to an isotropic liquid was observed at −0.7 °C. The molecular structures of these polymers were characterized by means of gel permeation chromatography and high‐resolution NMR studies, and the crystalline and liquid‐crystalline phases of the SCLC polymers were identified by differential scanning calorimetry, polarized optical microscopy, and X‐ray diffraction. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 984–997, 2003
Sulfobetaine‐containing diblock and triblock copolymers via reversible addition‐fragmentation chain transfer polymerization in aqueous media
Authors: Donovan Michael S. , Lowe Andrew B. , Sanford Taylor A. , McCormick Charles L.
Published: March 2003

A novel bifunctional acrylamido‐based reversible addition–fragmentation chain transfer (RAFT) chain‐transfer agent (CTA), N,N′‐ethylenebis[2‐(thiobenzoylthio)propionamide] (CTA2), has been synthesized and used for the controlled free‐radical polymerization of N,N‐dimethylacrylamide (DMA). A comparative study of CTA2 and the monofunctional CTA N,N‐dimethyl‐s‐thiobenzoylthiopropionamide (CTA1) has been conducted. Polymerizations mediated by CTA1 result in poly(N,N‐dimethylacrylamide) (PDMA) homopolymers with unimodal molecular weight distributions, whereas CTA2 yields unimodal, bimodal, and trimodal distributions according to the extent of conversion. The multimodal nature of the PDMAs has been attributed to termination events and/or chains initiated by primary radicals. The RAFT polymerization of DMA with CTA2 also results in a prolonged induction period that may be attributed to the higher local concentration of dithioester functionalities early in the polymerization. A series of ω‐ and α,ω‐dithioester‐capped PDMAs have been prepared in organic media and subsequently employed as macro‐CTAs for the synthesis of diblock and triblock copolymers in aqueous media with the zwitterionic monomer 3‐[2‐(N‐methylacrylamido)‐ethyldimethylammonio] propane sulfonate (MAEDAPS). Additionally, an ω‐dithioester‐capped MAEDAPS homopolymer has been used as a macro‐CTA for the block polymerization of DMA. To our knowledge, this is the first example of a near‐monodisperse, sulfobetaine‐containing block copolymer prepared entirely in aqueous media. The diblock and triblock copolymers form aggregates in pure water that can be dissociated by the addition of salt, as determined by 1H NMR spectroscopy and dynamic light scattering. In pure water, highly uniform, micellelike aggregates with hydrodynamic diameters of 71–93 nm are formed. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 1262–1281, 2003
New morphological control for thick, porous membranes with a plasma graft‐filling polymerization
Authors: Choi Yong‐Jin , Moon Seung‐Hyeon , Yamaguchi Takeo , Nakao Shin‐Ichi
Published: March 2003

Morphological control of membranes with plasma graft‐filling polymerization was proposed for thick, porous membranes. The morphology depended closely on the plasma within the membrane pore, which was determined by the plasma‐discharge power (PDP) and the gas pressure. The membrane morphology was investigated in terms of solvent composition in monomer solution, PDP, Ar pressure, and pore size of a substrate. Morphologies of membranes prepared were evaluated by a microscopic Fourier transform infrared mapping method. This study demonstrates that it is possible to control the membrane morphology by manipulating the plasma power and Ar pressure instead of morphological control by solvent‐dependent monomer activity. Additionally, through indirect methods this study reveals that plasma exists even in sub‐micropores (ca. 0.4 μm in diameter). © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 1216–1224, 2003
Block and star block copolymers by mechanism transformation 9: Preparation and characterization of poly(methyl methacrylate)/poly(1,3‐dioxepane)/polystyrene ABC miktoarm star copolymers by combination of reversible addition–fragmentation chain‐transfer polymerization and cationic ring‐opening polymerization
Authors: Li Yu‐Gang , Wang Yan‐Mei , Pan Cai‐Yuan
Published: March 2003

The miktoarm ABC star copolymer with three different branches, polystyrene (PS), poly(1,3‐dioxepane) (PDOP), and poly(methyl methacrylate) (PMMA), was successfully prepared. PS with two transfer groups, hydroxyl and dithiobenzoate groups [PS‐HECA‐SC(S)Ph], was synthesized by the reaction of a dithiobenzoate group at the end of PS with hydroxyethylene cinnamate (HECA) in tetrahydrofuran solution. Then, the cationic ring‐opening polymerization of 1,3‐dioxepane was initiated by triflic acid in the presence of PS‐HECA‐SC(S)Ph and diblock copolymer, PS‐PDOP, was formed. Finally, the diblock copolymer with the dithiobenzoate group situated between the two blocks was used in the reversible addition–fragmentation transfer (RAFT) process of methyl methacrylate (MMA). The miktoarm ABC star copolymer S(PS)(PDOP)(PMMA) was characterized by 1H NMR spectroscopy and gel permeation chromatography. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 1243–1250, 2003
Synthesis and optical properties of an azoaromatic, chromophore‐functionalized, oligomeric polyelectrolyte
Authors: Lee Taek Seung , Ahn Heungki , Park Won Ho , Sohn Byeong‐Hyeok , Kim Mi‐Jeong , Kim Dong‐Yu
Published: March 2003

A main‐chain, azoaromatic, chromophore‐functionalized polyelectrolyte with an oligomeric molecular weight was synthesized by the reaction of 4,4′‐azobispyridine and 1,6‐dibromohexane. The polyelectrolyte was designed to contain ionic groups to impart electrostatic self‐assembly with polyanion and azoaromatic groups for photoprocessability. The polymer solution exhibited a solvatochromic effect, having different absorption maxima in water (294 nm) and N,N‐dimethylformamide (400 nm). By a change in the counteranions of the bispyridinium groups, the solubility of the polymer could be controlled, and this made it possible to fabricate electrostatic assembled films or spin‐cast films for further applications. The direct photofabrication of laser‐induced interference patterns on polymer surfaces with large surface modulation was also investigated with an argon ion laser. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 1196–1201, 2003
Constitutional isomerism in polyamides derived from isophthaloyl chloride and 1,3‐diamine‐4‐chlorobenzene
Authors: García José M. , García Félix C. , Serna Felipe
Published: March 2003

Polyamides from isophthaloyl chloride and 1,3‐diamino‐4‐chlorobenzene with diverse constitutional order were obtained in a one‐stage synthesis varying the polymerization temperature and the monomer mixing modes. The constitutional order was calculated by 1H and 13C NMR spectroscopies. A model to determine the constitutional isomerism in these polycondensates was applied with the relevant kinetic reaction parameters obtained from the model reactions. The Monte Carlo technique was used to model the constitution along the polycondensation reaction as a function of the average polymerization degree. Constitution was determined by kinetic factors and not by thermodynamic ones. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 1202–1215, 2003
Iron‐based catalysts bearing bis(imido)–pyridine ligands for the polymerization of tert‐butyl acrylate
Authors: Castro Pascal M. , Lappalainen Kristian , Ahlgrén Markku , Leskelä Markku , Repo Timo
Published: March 2003

Iron(II) dichloride complexes bearing a tridentate nitrogen donor ligand were investigated for the homopolymerization of tert‐butyl acrylate after activation with methylaluminoxane. Two new complexes were synthesized, 2,6‐bis[1‐(cyclohexylimido)ethyl]pyridine iron chloride (FeCl2) and 2,6‐bis[1‐(isopropylimido)ethyl]pyridine FeCl2, and the single‐crystal X‐ray structure of the latter one was determined. Turnover frequencies of the catalysts during polymerization ranged from 36 to 241 cycles/mol/h. The obtained polymers exhibited weight‐average molecular weights ranging from 24,000 to 438,500 g/mol, and the molar mass distribution varied between 1.8 and 4.3. Activity of the catalytic system and the molar mass of the polymer are influenced by the ligand structure of the complexes as well as other polymerization conditions such as monomer concentration and temperature. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 1380–1389, 2003