bluuebunny/crossref_metadata_2025 huggingface dataset:
Werkstoffmodell zur Berechnung der mittleren Fließspannung bleihaltiger Messinge bei hohen Temperaturen
Authors: Hofmann U.
Published: August 2003

Ein einfaches Modell der Hochtemperaturumformung Pb‐haltiger Messinge wird vorgestellt. Es basiert auf Warmstauchversuchen, die mit den Legierungen Wieland‐Z36 (CuZn36Pb2As) und Wieland‐Z38 (CuZn40Pb2) durchgeführt wurden. Dabei wurden ein Temperaturbereich von 600 °C bis 850 °C und Umformgeschwindigkeiten zwischen 0,1/s und 10/s experimentell abgedeckt. Diese Parameter sind für die Praxis relevant, denn sie treten bei der Warmumformung von Messing – z. B. beim Gesenkschmieden – auf. Die Gültigkeit des Modells wird an anderen CuZnPb‐Legierungen überprüft.

Das Modell beschreibt die mittlere Fließspannung eines Pb‐haltigen Messings als Funktion der Temperatur und der Umformgeschwindigkeit. Der Werkstoff wird dabei als Verbund aus α‐ und β‐Phase aufgefasst. Die Phasen zeichnen sich durch unterschiedliche Umformeigenschaften aus. Ihre Volumenanteile sind die für die Warmumformung relevanten Gefügeparameter. Sie können aus dem Gleichgewichtszustandsdiagramm entnommen werden und hängen von der Temperatur und der chemischen Zusammensetzung der Legierung ab. Die Volumenanteile der Phasen bestimmen, welche Gefügekomponente das Verformungsverhalten des Gesamtverbundes dominiert.
Cast Pipe Joints of Fe‐15Mn‐5Si‐8Cr‐5Ni‐0.25C Shape Memory Alloy with High Carbon Content
Authors: Zhao M. , Li J. C. , Jiang Q.
Published: August 2003

Abstract: The cast pipe joint of the Fe‐15Mn‐5Si‐8Cr‐5Ni‐0.25C alloy was manufactured (the numbers in the composition denote the weight percentage of the elements while the weight percentage of Fe is the balance). The corresponding microstructure and shape memory effect are compared with those of a forged alloy. The results show that the cast joint has a good shape memory effect and may be industrially applied while the cast joint keeps jointing under a tensile force of 20 kN and a sealing pressure of 5 MPa. Moreover, it is found that the addition of nitrogen in the alloy doesn’t evidently improve the shape memory effect of the alloy.
Object‐oriented three‐dimensional hybrid grid generation
Authors: Athanasiadis A. N. , Deconinck H.
Published: August 2003

An algorithm is described for the generation of hybrid grids suitable for viscous computations around complex geometries. The definition of the geometry is given by the ISO standard STEP format. The grid generation is based on a hierarchical approach. The user‐specified parameters are given on all basic STEP entities and the definition is consistent across the complete geometry. Semi‐structured layers of prismatic cells are generated, starting from the viscous boundaries of the domain. The remaining volume is filled by an unstructured Delaunay algorithm with frontal node creation. Complex models have been successfully gridded, however, more testing is needed. Copyright © 2003 John Wiley & Sons, Ltd.
Parallel Delaunay mesh generation kernel
Authors: Chrisochoides Nikos , Nave Démian
Published: August 2003

We present the results of an evaluation study on the re‐structuring of a latency‐bound mesh generation algorithm into a latency‐tolerant parallel kernel. We use concurrency at a fine‐grain level to tolerate long, variable, and unpredictable latencies of remote data gather operations required for parallel guaranteed quality Delaunay triangulations. Our performance data from a 16 node SP2 and 32 node Cluster of Sparc Workstations suggest that more than 90% of the latency from remote data gather operations can be masked effectively at the cost of increasing communication overhead between 2 and 20% of the total run time. Despite the increase in the communication overhead the latency‐tolerant mesh generation kernel we present in this paper can generate tetrahedral meshes for parallel field solvers eight to nine times faster than the traditional approach. Copyright © 2003 John Wiley & Sons, Ltd.
A method for hexahedral mesh shape optimization
Authors: Knupp Patrick M.
Published: August 2003

Methods for improving the quality of all‐hexahedral unstructured meshes by node‐movement strategies have, until recently, been lacking. Laplacian smoothing, while easily implemented and well‐known, fails to guarantee improvement of mesh quality and may result in inverted elements where none existed before. A method for improving unstructured hexahedral mesh shape‐quality that guarantees untangled elements is proposed. The method is based on optimization of an objective function built from the quality of individual hexahedral elements. The shape‐quality measure for hexahedral elements is based on the condition number of a set of Jacobian metrics associated with the element. The theory of the condition number quality metric and of the objective function are reviewed. A numerical optimization procedure to find the improved‐quality mesh is described. The purpose of this paper is to demonstrate the robustness of the method. We do so by giving a realistic example. The method has also been successfully applied to dozens of meshes on complex geometries. Published in 2003 by John Wiley & Sons, Ltd.
Interpolating and meshing 3D surface grids
Authors: Laug P. , Borouchaki H.
Published: August 2003

In the boundary representation (B‐Rep) model, a three‐dimensional (3D) surface is defined by a set of ‘simpler surfaces’ called ‘patches’. Although there are many different ways to specify a patch, a common case is that of a 4‐sided patch represented by a structured grid of points. For instance, this kind of data can easily be obtained from a CAD system, as it is the mapping of regularly spaced points in a rectangular parametric domain. It can also be obtained from some particular 3D scanning devices. Non‐rectangular topologies may also be encountered, for instance the 3‐sided patch which can be considered as a degenerate case of the 4‐sided patch (one side being of zero length). In this paper, we use the Coons method to build a surface interpolating the vertices of such a grid. The continuity of this parameterization makes it suitable for our indirect approach to surface meshing, which is generally based on the generation of an anisotropic mesh in the parametric space. Moreover, the indirect approach has been extended to the construction of anisotropic geometric surface meshes in 3D space, allowing an accurate geometric representation of the surface with a minimal number of elements. Several examples demonstrate the capabilities of this method. Copyright © 2003 John Wiley & Sons, Ltd.
Accounting for curved domains in mesh adaptation
Authors: Li Xiangrong , Shephard Mark S. , Beall Mark W.
Published: August 2003

This paper presents a procedure to project vertices created by refining straight sided tetrahedra to appropriate locations on curved model boundaries. Although many of the vertices introduced by refinement of mesh edges and faces on the boundary of the model can easily be projected to the model geometry, there are situations where this projection creates invalid elements. To ensure the ability to place those vertices on the model boundary an efficient two‐step procedure has been developed. The first step applies local mesh modification operations such as collapse and swap to incrementally project vertices. It is shown that the effective application of mesh modifications that will yield a mesh in which the vertex in question can be projected to the boundary must focus on ensuring the vertex in question moves at least as far as the plane on which the mesh would have element shapes degrade to zero volume. The second step applies a generalized local cavity triangulation algorithm to ensure the success of the process when the set of local mesh modifications considered is unable to project the vertex to the boundary. Copyright © 2003 John Wiley & Sons, Ltd.
Mesh‐based geometry
Authors: Owen Steven J. , White David R.
Published: August 2003

A systematic approach to building a complete geometric and topologic representation of a model given only the finite element (FE) description is proposed. The objective of the proposed system is to provide a geometry foundation for existing finite element based models so that standard mesh generation tools can be used without requiring CAD‐based modelling systems such as ACIS or other proprietary commercial tools. To accomplish this, a method for extracting topology from the FE model is proposed. Topology entities including volumes, surfaces, curves and vertices are built based on user‐defined boundary conditions and surface features. Curve and surface geometry is described by either linear triangular facets or G1 continuous 4th‐order Bezier patches. Integration of the proposed mesh‐based geometry (MBG) system into an existing mesh generation toolkit is described. Sample applications and examples of MBG are presented. Published in 2003 by John Wiley & Sons, Ltd.
An algorithm oriented mesh database
Authors: Remacle Jean‐François , Shephard Mark S.
Published: August 2003

In this paper, we present a new point of view for efficiently managing general mesh representations. After reviewing some mesh representation basics, we introduce the new Algorithm Oriented Mesh Database (AOMD). Some hypotheses are taken in order to be able to manage any set of adjacencies. Then, we present the design of the AOMD in terms of classes and algorithms. The Standard Template Library (STL) is used for managing the AOMD. Finally, we present some results and discuss technical choices that were made in the AOMD design and implementation. AOMD is available as open source at http: //www.scorec.rpi.edu/AOMD. Copyright © 2003 John Wiley & Sons, Ltd.
The Safe Schools/Healthy Students (SS/HS) initiative: Lessons learned from implementing comprehensive youth development programs
Authors: Furlong Michael , Paige Leslie Z. , Osher David
Published: August 2003

This article provides an overview of a special issue of Psychology in the Schools that examines the implementation of the Safe Schools/Healthy Students (SS/HS) Initiative in seven local communities. An overview of the SS/HS Initiative is provided. Critical lessons learned from the seven sites are discussed with a focus on the special role that school psychologists can play in implementing these complex violence prevention programs. © 2003 Wiley Periodicals, Inc. Psychol Schs 40: 447–456, 2003.
Promoting safe schools and healthy students in rural Pennsylvania
Authors: Welsh Janet , Domitrovich Celene E. , Bierman Karen , Lang Joann
Published: August 2003

The Safe Schools/Healthy Students (SS/HS) Initiative is currently underway in the Tyrone Area School District. Tyrone is a rural community characterized by high levels of poverty, unemployment, and youth problems including substance use and alienation from school and community. Its strengths include strong administrative leadership and prior successful collaboration with Penn State University. The goals of the SS/HS Initiative involve reducing risk and building competencies for students and their families through integration of law enforcement and mental health into school‐based prevention efforts. The programs include early childhood, elementary, and secondary school components; and also district‐wide components that span these developmental levels. Despite challenges associated with the integration of different professional perspectives into the school environment, the Tyrone SS/HS Initiative has been quite successful. Program evaluation is varied, and reflects the different programs and student populations served. Currently, plans for sustaining and institutionalizing SS/HS programs are underway in Tyrone. © 2003 Wiley Periodicals, Inc. Psychol Schs 40: 457–472, 2003.
Implementation of school‐based wellness centers
Authors: Guerra Nancy G. , Williams Kirk R.
Published: August 2003

This article describes the planning, implementation, and evaluation of school‐based Wellness Centers operated by the Riverside Unified School District in Riverside, CA, as part of the Safe Schools/Healthy Students Initiative funded by the Substance Abuse and Mental Health Services Administration (SAMHSA). We describe the program as planned in terms of the theoretical model for the intervention and the evaluation design, and discuss the actual implementation including accomplishments and challenges. The program was designed to promote positive development and wellness for individual students via self‐ and teacher‐referrals for personal and mental health problems handled through a case management and referral process, support groups, and other activities such as after‐school programs, mentoring, tutoring, and parent training. An effort was also made to promote wellness at the school level by providing wellness campaigns, information, and compatible policies and procedures designed to enhance healthy development. Our observations are based on a qualitative assessment that was a component of the evaluation. A more detailed evaluation examining the impact of school‐wide and student‐focused activities on academic and behavioral outcomes is currently underway. However, we do include comments from students suggesting that the Wellness Center concept holds much promise for school‐based mental health and violence prevention services. © 2003 Wiley Periodicals, Inc. Psychol Schs 40: 473–487, 2003.
Creating synergy through collaboration: Safe schools/ healthy students in salinas, california
Authors: Elizondo Fernando , Feske Ken , Edgull Dana , Walsh Kelle
Published: August 2003

In Salinas, a city of 150,000 on the Central Coast of California, an $8 million federal grant program is helping children and their families grapple with issues pertaining to violence, substance abuse, mental health, and academic success. In just two years, the program has helped educators and service providers deter school crime, provide on‐campus therapy to troubled youth, increase participation in parenting programs, and decrease truancy at several schools. Most importantly, the Salinas initiative has helped providers coordinate services to children and families who need them most. Project directors say that approach will be crucial as they search for new ways to sustain Safe Schools/Healthy Students (SS/HS)‐funded programs. © 2003 Wiley Periodicals, Inc. Psychol Schs 40: 503–513, 2003.
Face fidelity: Perspectives from a local evaluation of the Safe Schools/Healthy Students initiative
Authors: Giancola Susan P. , Bear George G.
Published: August 2003

The creation of a federal Safe Schools/Healthy Students (SS/HS) Initiative reflects a growing level of concern across the United States that many children do not feel safe at school, and that teachers must receive a new level of training to better equip themselves to manage a diverse student population. PROJECT BLUE was funded during the first phase of this initiative and proposed to provide students in its District with a range of services to improve school safety, decrease school violence, decrease alcohol and drug use, and improve student mental health. The local evaluation team collected information regarding project implementation and its impact on school safety, school climate, and teacher preparedness to manage student misbehavior. Selected results are highlighted in the article. However, the primary purpose of this article is to document lessons learned from the evaluation of this project. Lessons learned are presented in four areas: leadership, communication, system change efforts, and local evaluation of federal initiatives. © 2003 Wiley Periodicals, Inc. Psychol Schs 40: 515–529, 2003.
Rural underpinnings for resiliency and linkages (rural): A safe schools/healthy students project
Authors: Paige Leslie Z. , Kitzis Stephen N. , Wolfe Joyce
Published: August 2003

Rural Underpinnings for Resiliency and Linkages (RURAL) is an example of a Safe Schools/Healthy Students (SS/HS) project. RURAL provides services to children and families in a rural Kansas county. The county's rates of juvenile alcohol and illicit drug use are higher than state averages. The RURAL project was designed to enhance existing partnerships among three school districts, the local community mental health center, law enforcement, the regional prevention center, and Fort Hays State University. A significant number of evidence‐based strategies were implemented in the schools and community in a short period of time. Using a public health approach to increase school safety and promote healthy behaviors, RURAL introduced strategies designed to provide universal prevention for the school population, early intervention for at‐risk children and families, and intensive services for those with the greatest needs. Services were provided to students (preschool–young adults) and their families. School psychologists held key roles in the development, implementation, and management of the project. Preliminary evaluation findings are presented, and the importance of local process and outcome evaluation is discussed. © 2003 Wiley Periodicals, Inc. Psychol Schs 40: 531–547, 2003.
Building community connections for youth to reduce violence
Authors: Telleen Sharon , Maher Susan , Pesce Rosario C.
Published: August 2003

The Safe Schools/Healthy Students Initiative in Morton High School District 201, Cicero, IL, used a social ecological systems perspective to implement its goals. Social‐emotional learning and violence‐prevention strategies were provided at the levels of the community, school, and individual. Creation of a safe school environment cut across developmental levels from preschool through high school. Intervention activities were universal/preventive, school, and targeted/individual. Finally, the project sought to develop a consortium infrastructure to institutionalize and sustain integrated services. © 2003 Wiley Periodicals, Inc. Psychol Schs 40: 549–563, 2003.
Synthesis and properties of the ionomer diblock copolymer poly(4‐vinylbenzyl triethyl ammonium bromide)‐b‐polyisobutene
Authors: Ma Yuhong , Wu Guangying , Yang Wantai
Published: August 2003

A new amphiphilic diblock copolymer containing an ionomer segment, poly[(4‐vinylbenzyl triethyl ammonium bromide)‐co‐(4‐methylstyrene)‐co‐(4‐bromomethylstyrene)]‐b‐polyisobutene [poly(4‐VBTEAB)‐b‐PIB], was synthesized by the chemical modification of poly(4‐methylstyrene)‐b‐polyisobutene [poly(4‐MSt)‐b‐PIB]. First, the 4‐methylstyrene moiety in poly(4‐MSt)‐b‐PIB was brominated with azobisisobutyronitrile as an initiator at 60 °C in CCl4, and then the highly reactive benzyl bromide groups were ionized by a reaction with triethylamine in a toluene/isopropyl alcohol (80/20 v/v) mixture at about 85 °C to produce the ionomer diblock copolymer poly(4‐VBTEAB)‐b‐PIB. The solubility of the ionomer block copolymer was quite different from that of the corresponding poly[(4‐methylstyrene)‐co‐(4‐bromomethylstyrene)]‐b‐polyisobutene {poly[(4‐MSt)‐co‐(4‐BrMSt)]‐b‐PIB}. Transmission electron microscopy observations demonstrated that all three diblock copolymers had microphase‐separation structures in which polyisobutene (PIB) domains existed in the continuous phase of the poly(4‐methylstyrene) segment or its derivative segment matrix. Dynamic mechanical thermal analysis measurements showed that poly[(4‐MSt)‐co‐(4‐BrMSt)]‐b‐PIB had two glass‐transition temperatures (Tg's), −56 °C for the PIB segment and 62 °C for the poly[(4‐MSt)‐co‐(4‐BrMSt)] domain, whereas poly(4‐VBTEAB)‐b‐PIB showed one Tg at −8 °C of the PIB domain; Tg of the poly[(4‐vinylbenzyl triethyl ammonium bromide)‐co‐(4‐methylstyrene)‐co‐(4‐bromomethylstyrene)] domain was not observable because of the strong ionic interactions resulting in a higher Tg and a retention of modulus up to 124 °C. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 2755–2764, 2003
Self‐polyaddition of triethylsilyl perfluoroisopropenyl ether
Authors: Fujiwara Hirotada , Narita Tadashi , Hamana Hiroshi
Published: August 2003

The results on radical self‐polyaddition reactivity of two trialkylsilyl perfluoroisopropenyl ethers, triethysilyl perfluoroisopropenyl ether [CF2C(CF3)OSi(C2H5)3] (FTEE) and dimethylphenylsilyl perfluoroisopropenyl ether [CF2C(CF3)OSi(CH3)2C6H5] (DMPE), and two perfluoroisopropenyl carboxylates, 2‐butyroxypentafluoropropene [CF2C(CF3)OCOC3H7] (BuFPP) and 2‐(methoxyacetoxy)pentafluoropropene [CF2C(CF3)OCOCH2OCH3] (MFPP), are described. Radical self‐polyaddition of FTEE afforded a polymer as high as 1.87 × 104 in molecular weight in the presence of radical generators such as benzoyl peroxide and di‐tert‐butyl peroxide. DMPE gave only addition products with initiating radicals. BuFPP and MFPP scarcely yielded even addition products with radical. The mechanism that the self‐polyaddition of FTEE was initiated by the addition of radical onto the perfluoroisopropenyl group followed by a 1,5‐shift to afford a methyl radical that attacked the perfluoroisopropenyl group of another FTEE molecule is proposed. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 2743–2754, 2003
Polymer proton‐conduction systems based on commercial polymers. I. Synthesis and characterization of hydrogenated styrene–butadiene block copolymer and isobutylene isoprene rubber systems
Authors: Nácher A. , Escribano P. , Del Río C. , Rodríguez A. , Acosta J. L.
Published: August 2003

This work describes the synthesis and characterization of two nonfluorinated proton‐conducting polymer systems, one consisting of a hydrogenated styrene–butadiene rubber (HSBR) block copolymer and the other consisting of an HSBR blend with isobutylene isoprene rubber for the improved mechanical stability of the final product. The films obtained were crosslinked, sulfonated, and microstructurally and electrically characterized. In addition, water and methanol crossover was determined, the results being compared with those of Nafion 117. The properties measured in the different samples confirmed that these systems may constitute a valid alternative to commercial membranes, being low‐cost and less polluting and having a lower methanol crossover. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 2809–2815, 2003
Essential role of chain ends in the nylon‐6/poly(ethylene terephthalate) exchange
Authors: Samperi Filippo , Puglisi Concetto , Alicata Rossana , Montando Giorgio
Published: August 2003

A combination of NMR and matrix‐assisted laser desorption/ionization time‐of‐flight mass spectrometry (MALDI‐TOF) techniques were suitable tools for examining the exchange reactions that occur during the melt‐mixing of nylon‐6 and poly(ethylene terephthalate) (Ny6/PET) blends in the presence of p‐toluene sulfonic acid (TsOH) at 285 °C. Some researchers believe that TsOH is an efficient catalyst for the amide–ester exchange reactions in PET/Ny6 and PET/nylon‐66 blends in the molten state. Instead, we have found that TsOH is able to react in the molten state with PET, yielding PET oligomers terminated with carboxyl groups. Because the latter oligomers can quickly react with Ny6 producing a Ny6/PET copolymer, the role of TsOH in the melt‐mixing process is not that of a catalyst but of a reactant. Our study allowed the structural identification of the Ny6/PET copolyesteramide produced in the exchange as a function of melt‐mixing time. The results revealed the essential role of carboxyl end groups in the exchange reaction between Ny6 and PET and allowed a detailed mechanism for this reaction. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 2778–2793, 2003
Luminescent copoly(aryl ether)s consisting of alternate oxadiazole and 1,4‐distyrylbenzene derivatives: Synthesis and characterization
Authors: Yu Yun‐Hao , Chen Yun
Published: August 2003

In an effort to decrease the electron‐injection barrier from the anode electrode, four copoly(aryl ether)s (P1–P4), consisting of alternating isolated electron‐transporting [2,5‐diphenyl‐1,3,4‐oxadiazole for P1 and P3 and 5,5′‐diphenyl‐2,2′‐p‐(2,5‐bishexyloxyphenylene)‐bis‐1,3,4‐oxadiazole for P2 and P4] and emitting chromophores (1,4‐distyryl‐2,5‐dihexyloxybenzene for P1 and P2 and 1,4‐distyryl‐2,5‐dihexylbenzene for P3 and P4), have been synthesized by the nucleophilic displacement reaction between bisfluoride and bisphenol monomers. They are basically amorphous materials with 5% weight‐loss temperature above 400 °C. The photoluminescence spectra and quantum yields of these copolymers are dependent on the compositions of the two isolated fluorophores. The highest occupied molecular orbital and lowest unoccupied molecular orbital energy levels of these copolymers have been estimated from their cyclic voltammograms. All the observations directly prove that the oxidation starts at the hole‐transporting segments. The electron affinity can be enhanced by the introduction of isolated electron‐transporting segments that lead to a charge‐injection balance. Single‐layer light‐emitting diodes (Al/P1–P4/ITO glass) have been fabricated. P1 and P2 reveal blue electroluminescence, and P3 and P4 reveal purple‐blue electroluminescence. Moreover, the incorporation of bisoxadiazole units increases the electron affinity and reduces the turn‐on electric field better than one oxadiazole unit. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 2765–2777, 2003
Copolymerization of diglycidyl ether of bisphenol A with γ‐butyrolactone catalyzed by ytterbium triflate: Shrinkage during curing
Authors: Mas Cristina , Ramis Xavier , Salla Josep Maria , Mantecón Ana , Serra Angels
Published: August 2003

Diglycidyl ether of bisphenol A (DGEBA) was cured with γ‐butyrolactone (γ‐BL) with ytterbium triflate as a catalyst. The curing was studied with differential scanning calorimetry, Fourier transform infrared (FTIR), and thermomechanical analysis. FTIR studies confirmed that four elemental reactions took place during the curing process: the formation of a spiroorthoester (SOE) by the reaction of DGEBA with γ‐BL, the homopolymerization of SOE, the homopolymerization of DGEBA, and the copolymerization of SOE and DGEBA. Moderate proportions of γ‐BL produced materials with higher glass‐transition temperatures, and the curing occurred with lower shrinkage after gelation because of the polymerization of SOE, with near‐zero shrinkage during the final stages of the curing. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 2794–2808, 2003
Graft copolymers by acyclic diene metathesis and atom transfer radical polymerization techniques
Authors: O'Donnell Patrick M. , Wagener Kenneth B.
Published: August 2003

Precise graft copolymer architectures were achieved by combining the macromonomer technique with the acyclic diene metathesis (ADMET) reaction. These well‐defined copolymer structures were the result of proper monomer design before metathesis polymerization. Features such as length of the graft, nature, and concentration of the graft site along the backbone were manipulated via the combination of living atom transfer radical polymerization methods with ADMET chemistry. Furthermore, the physical behavior of these materials was altered such that they presented dissimilar thermal properties of either the homopolymers or random copolymers. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 2816–2827, 2003
A difference of six orders of magnitude: A reply to “the magnitude of the fragmentation rate coefficient”
Authors: Wang Aileen R. , Zhu Shiping , Kwak Yungwan , Goto Atsushi , Fukuda Takeshi , Monteiro Michael S.
Published: August 2003

There has been an ongoing debate regarding the mechanism that causes rate retardation phenomena observed in some reversible addition‐fragmentation transfer (RAFT) polymerization systems. Some attribute the retardation to slow fragmentation of adduct radicals, others attribute it to fast fragmentation coupled with cross‐termination between propagating and adduct radicals. There exists a difference of six orders of magnitude (10−2 versus 104/s) in the reported values of the fragmentation rate constant (kf0) for virtually similar RAFT systems of PStSC · (Ph)SPSt. In this communication, we explain the estimates of kf ∼ 104/s and the choices of the rate constant in modeling based on experimental polymerization rate and radical concentration data. The use of kf ∼ 10−2/s in the model results in a calculated adduct radical concentration level of 10−4 to 10−3 mol/L, which appears to directly contradict the reported electron spin resonance (ESR) data in the range of <10−6 mol/L. We hope that this open discussion can stimulate more effort to resolve this outstanding difference. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 2833–2839, 2003
The reversible addition‐fragmentation chain transfer process and the strength and limitations of modeling: Comment on “the magnitude of the fragmentation rate coefficient”
Authors: Barner‐Kowollik Christopher , Coote Michelle L. , Davis Thomas P. , Radom Leo , Vana Philipp
Published: August 2003

There is appreciable uncertainty concerning the magnitude of the fragmentation rate coefficient of the intermediate radical in reversible addition‐fragmentation chain transfer (RAFT) polymerizations. A large proportion of the experimental and theoretical evidence suggests that it is a stable species with a lifetime longer than 0.0001 s. This is particularly the case when the intermediate macro‐RAFT radical is stabilized by a phenyl group attached to the radical center or has a poor leaving group. Although the occurrence to some extent of irreversible termination reactions cannot be excluded, we argue that such reactions are more likely to be a result of slow fragmentation of the intermediate macro‐RAFT radical. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 2828–2832, 2003
Studies on calcium‐containing poly(urethane ether)s
Authors: Jayakumar R. , Lee Y.‐S. , Nanjundan S.
Published: August 2003

The calcium salt of mono(hydroxyethoxyethyl)phthalate [Ca(HEEP)2] was synthesized by the reaction of diethylene glycol, phthalic anhydride, and calcium acetate. Calcium‐containing poly(urethane ether)s (PUEs) were synthesized by the reaction of hexamethylene diisocyanate (HMDI) or tolylene 2,4‐diisocyanate (TDI) with a mixture of Ca(HEEP)2 and poly(ethylene glycol) (PEG300 or PEG400) with di‐n‐butyltin dilaurate as a catalyst. A series of calcium‐containing PUEs of different compositions were synthesized with Ca(HEEP)2/PEG300 (or PEG400)/diisocyanate (HMDI or TDI) molar ratios of 2:2:4, 3:1:4, and 1:3:4 so that the coating properties of the PUEs could be studied. Blank PUEs without calcium‐containing ionic diols were also prepared by the reaction of PEG300 or PEG400 with HMDI or TDI. The PUEs were well characterized by Fourier transform infrared, 1H and 13C NMR, solid‐state cross‐polarity/magic‐angle‐spinning 13C NMR, viscosity, solubility, and X‐ray diffraction studies. The thermal properties of the polymers were also studied with thermogravimetric analysis and differential scanning calorimetry. The PUEs were applied as top coats on acrylic‐coated leather, and their physicomechanical properties were also studied. The coating properties of PUEs, such as the tensile strength, elongation at break, tear strength, water vapor permeability, flexing endurance, cold crack resistance, abrasion resistance, color fastness, and adhesive strength, were better than the standard values. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 2865–2878, 2003
Synthesis and enzymatic degradation of 2‐methylene‐1,3‐dioxepane and methyl acrylate copolymers
Authors: Sun L. F. , Zhuo R. X. , Liu Z. L.
Published: August 2003

Copolymers of 2‐methylene‐1,3‐dioxepane (MDO) and methyl acrylate (MA) containing ester units both in the backbone and as pendant groups were synthesized by free‐radical copolymerization. The influence of reaction conditions such as the polymerization time, temperature, initiator concentration, and comonomer feed ratio on the yield, molecular weight, and copolymer composition was investigated. The structure of the copolymers was confirmed by 1H NMR, 13C NMR, and IR spectroscopy. Differential scanning calorimetry indicated that the copolymers had a random structure. An NMR study showed that hydrogen transfer occurred during the copolymerization. The reactivity ratios of the comonomers were rMDO = 0.0235 and rMA = 26.535. The enzymatic degradation of the copolymers obtained was carried out in the presence of proteinase K or a crude enzyme extracted from earthworms. The experimental results showed that the higher ester molar percentage in the backbone caused a faster degradation rate. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 2898–2904, 2003
Synthesis of amphiphilic poly(para‐phenylene)s by Suzuki polycondensation
Authors: Zhang Changmei , Schlaad Helmut , Schlüter A. Dieter
Published: August 2003

1,4‐Dibromobenzenes carrying nonpolar hexoxy and polar oligo(ethylene glycol) side chains were subjected to Suzuki polycondensation with a benzene‐1,4‐bisboronic acid ester to produce high‐molar‐mass poly(para‐phenylene)s. The molar masses were determined with size exclusion chromatography with conventional polystyrene and universal calibration. These novel amphiphilically equipped rigid‐rod polymers have the potential to segregate lengthwise into polar and nonpolar domains, a property that has only rarely been described, and promise to exhibit novel interesting supramolecular properties. The oligo(ethylene gylcol) side chains terminate with a silyl‐protected alcohol group, and its deprotection on the polymer was proven to proceed quantitatively. This not only led to a further polarity increase but allows us to attach even more polar (e.g., charged) units in future projects. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 2879–2889, 2003
Synthesis of side‐chain liquid‐crystalline homopolymers and triblock copolymers with p‐methoxyazobenzene moieties and poly(ethylene glycol) as coil segments by atom transfer radical polymerization and their thermotropic phase behavior
Authors: He Xiaohua , Zhang Hailiang , Yan Deyue , Wang Xiayu
Published: August 2003

A series of side‐chain liquid‐crystalline (LC) homopolymers of poly[6‐(4‐methoxy‐4′‐oxy‐azobenzene) hexyl methacrylate] with different degrees of polymerization were synthesized by atom transfer radical polymerization (ATRP), which were prepared with a wide range of number‐average molecular weights from 5.1 × 103 to 20.6 × 103 with narrow polydispersities of around 1.17. Thermal investigation showed that the homopolymers exhibit two mesophases, a smectic phase, and a nematic phase, and the phase‐transition temperatures of the homopolymers increase clearly with increasing molecular weights. A series of novel LC coil triblock copolymers with narrow polydispersities was synthesized by ATRP, and their thermotropic phase behavior was investigated with differential scanning calorimetry and polarized optical microscopy. The LC coil triblocks were designed to have an LC conformation of poly[6‐(4‐methoxy‐4′‐oxy‐azobenzene) hexyl methacrylate] with a wide range of molecular weights from 3.5 × 103 to 1.7 × 104 and the coil conformation of poly(ethylene glycol) (PEG) (number‐average molecular weight: 6000 or 12,000) segment. Their characterization was investigated with 1H NMR, Fourier transform infrared spectra, and gel permeation chromatography. Triblock copolymers exhibited a crystalline phase, a smectic phase, and a nematic phase. The phase‐transition temperatures from the smectic to nematic phase and from the nematic to isotropic phase increased, and the crystallization of PEG depressed with increasing molecular weight of the LC block. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 2854–2864, 2003
Design and synthesis of a thermally stable second‐order nonlinear optical chromophore and its poled polymers
Authors: Qin Anjun , Yang Zhou , Bai Fenglian , Ye Cheng
Published: August 2003

A multiple charge‐transfer second‐order nonlinear optical (NLO) chromophore 2,3‐bis(4‐aminophenyl)‐5,6‐dicyanopyrazine (BAPDCP) was successfully designed and synthesized. It was characterized by 1H NMR, mass spectrometry, Fourier transform infrared spectroscopy, and elemental analysis. The first hyperpolarizability β of BAPDCP was measured with the Hyper–Rayleigh scattering technique, which was 123.5 × 10−30 esu. The donor‐embedded prepolyimide and prepolyurea were also synthesized by a polyaddition reaction. Thermogravimetric analysis and differential scanning calorimetry demonstrated that either the chromophore or the polymers have fine thermal stability. The thin films of prepolymers were prepared by coating on ITO glass substrate and poled by corona poling at elevating temperature. The second‐order NLO coefficients d33 of the films were measured by in situ second‐harmonic generation measurements. The d33 were deduced as 27.7 and 16.5 pm/V for polyurea and polyimide at 1064 nm fundamental wavelength, respectively. The onset depoling temperature of the polyimide and polyurea were both as high as 200 °C. To understand the temperature effect to the orientation thermal stability of polyimide, two films were treated at different final poling temperatures. The depoling experimental results showed that the orientation stability is higher, as raising the final treated temperature but the d33 value are almost similar. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 2846–2853, 2003
Fluorinated vinyl ethers as new surface agents in the photocationic polymerization of vinyl ether resins
Authors: Bongiovanni R. , Sangermano M. , Malucelli G. , Priola A. , Leonardi A. , Ameduri B. , Pollicino A. , Recca A.
Published: August 2003

The syntheses of fluorinated vinyl ethers (H2CCHOCH2CH2CnF2n+1, n = 6 or 8) and their copolymerizations with bis(4‐vinyloxybutyl) isophthalate are reported. The fluorinated monomers were prepared by the transetherification of ethyl vinyl ether and fluorinated alcohols in a 75% yield. Added in low concentrations (0.1–3.0 wt %) to formulations containing bis(4‐vinyloxybutyl) isophthalate, they did not affect the kinetics of the cationic photopolymerization. The cured films were transparent and showed interesting properties in terms of wettability, hardness, cross‐cut adhesion, and chemical inertness. The fluoromonomers increased the hydrophobicity of the film surface, whereas the adhesion on various substrates such as glass and wood was unchanged. An increase in the methyl ethyl ketone resistance was also observed. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 2890–2897, 2003
Heterogeneous nucleation on the crystallization poly(ethylene terephthalate)
Authors: Bian Jie , Ye Sheng‐Rong , Feng Lin‐Xian
Published: August 2003

The crystallization behavior of poly(ethylene terephthalate) (PET) with disodium terephthalate (DST) as nucleating agent was investigated. A detailed analysis of the crystallization course from the melt was made with the Avrami expression. The results demonstrated that DST additive can promote the PET crystallization rate in its entire crystallizable temperature range, and the acceleration degree of DST decreases with increasing temperature after a temperature higher than 180 °C. The values of the Avrami exponent indicated that the crystallization mode in Avrami theory is not suitable for the crystallization of these polymers, and the mechanism of the heterogeneous nucleation on PET crystallization is discussed. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 2135–2144, 2003
Effects of plasticizers on novel electromechanical actuations with different poly(vinyl chloride) gels
Authors: Uddin Md. Zulhash , Watanabe Masashi , Shirai Hirofusa , Hirai Toshihiro
Published: August 2003

Four different plasticizers were applied to make different poly(vinyl chloride) (PVC) gels, poly(vinyl chloride)‐bis(2‐ethylhexyl)phthalate (PVC‐DOP), poly(vinyl chloride)‐di‐n‐butylphthalate, poly(vinyl chloride)‐bis(2‐ethylhexyl)adipate, and poly(vinyl chloride)‐tris(2‐ethylhexyl)trimellitate. In our previous work, we reported that PVC‐DOP gel exhibits novel and reversible deformations of creeping and jointlike bending induced by direct current electric fields. In this article, we scrutinize the effects of plasticizers on electromechanical actuations, that is, reversible creeping and bending actuation with four of the different aforementioned gels. We measured the relative creeping distance, creeping area, creeping velocity, current observed, and bending angle as a function of applied electric fields for different PVC gels and found significant differences among them. To explain these variations, we compared the utility of plasticizers on the basis of the properties of different PVC gels, such as plasticizer‐retention ability, bending modulus, elongation at break, and the dielectric constant. The mentioned properties of the PVC gels played vital roles on their electromechanical actuations. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 2119–2127, 2003
Numerical simulation of coupled‐stress case II diffusion in one dimension
Authors: Vijalapura Prashanth K. , Govindjee Sanjay
Published: August 2003

This article is concerned with the robust and efficient numerical simulation of case II diffusion, which constitutes an important regime of solvent diffusion into glassy polymers. Even in the one‐dimensional case considered here, the numerical simulation of case II diffusion is made difficult by the extreme nonlinearities and coupling in the governing model equations due to a nonlinear flux law needed to produce sharp solvent fronts, a concentration‐dependent relaxation time of the polymer used to model the glass‐rubber transition, and coupling between the diffusion and deformation phenomena. Having an efficient and accurate solution to such equations is central to advancing a clear understanding of the meaning of such models. The difficulties due to coupling and nonlinearities are highlighted by the consideration of a specific, normalized, one‐dimensional case II diffusion model laid out in a general framework of balance laws. Issues such as the stiffness of the spatially discrete differential algebraic equations obtained from the finite element discretization of the governing equations and their bearing on the choice of time‐stepping schemes are discussed. The key requirements of numerical schemes, namely, robustness and efficiency, are addressed by the use of an implicit, adaptive, second‐order backward differentiation formula with error control for time discretization. Error control is used to maximize the step size to satisfy a target error and the radius of convergence requirements while nonlinear algebraic equations are solved at each time step. An example of an initial boundary value problem is solved numerically to show that the chosen model reproduces case II behavior and to validate that the stated objectives for the numerical simulation are met. Finally, the features and numerical implementation of this model are compared with those of a closely related case II diffusion model due to Wu and Peppas. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 2091–2108, 2003
Glassy polymer‐sorption phenomena measured with a quartz crystal microbalance technique
Authors: Zhang C. , Cappleman B. P. , Defibaugh‐Chavez M. , Weinkauf D. H.
Published: August 2003

The quartz crystal microbalance (QCM) method is applied to the measurement of CO2 sorption in glassy poly(ethylene terephthalate) (PET), poly(methyl methacrylate), and polysulfone. Polymer thin films in the thickness range of 350–550 nm are prepared by spin‐casting onto the quartz crystal devices. Sorption isotherms at temperatures below the glass transition are analyzed with the dual‐mode sorption model. As‐cast, quenched, and slow‐cooled thermal‐conditioning protocols yield consistent trends in the sorption level, namely, as‐cast > quenched > slow‐cooled. The sorption levels and model results for the quenched‐conditioned samples measured with QCM compare favorably with those reported from the pressure‐decay and gravimetric methods on thick films. With extended analysis of PET, the QCM technique is also useful for the exploration of the temperature dependence associated with gas sorption in glassy polymer systems. Measured heats of sorption and the collapse of the Langmuir component near the PET glass‐transition temperature agree with those reported previously. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 2109–2118, 2003
Terraces on banded spherulites of polyhydroxyalkanoates
Authors: Xu Jun , Guo Bao‐Hua , Chen Guo‐Qiang , Zhang Zeng‐Min
Published: August 2003

On banded spherulites of poly(3‐hydroxybutyrate) and its copolymers, fine circles were observed between either cross‐polarizers or without polarizers. Atomic force microscopy was applied to confirm that these circles are terraces with heights up to several hundred nanometers rather than cracks. Real‐time observation demonstrated that the terrace forms at the front of the growing spherulites just before or exactly when two spherulites impinge on each other. Terraces were observed on the spherulites crystallized from melt confined between glass or polyimide slides rather than poly(ethylene terephthalate) slides. The formation of the terraces may have resulted from instability of the moving boundary of the melt film confined between the spherulite surface and cover slide. Wettability of the substrate played an important role in the formation of the terraces. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 2128–2134, 2003
Properties of poly(dimethylsiloxane)/hydrogel multicomponent systems
Authors: Abbasi F. , Mirzadeh H.
Published: August 2003

The properties of surface‐ and bulk‐modified poly(dimethylsiloxane) (PDMS) were examined. Laser‐induced surface grafting of poly(2‐hydroxyethyl methacrylate) (PHEMA) on PDMS and a sequential method for preparation of interpenetrating polymer networks of PDMS/PHEMA were, respectively, used for surface and bulk modifications. The hydrogel content and water‐uptake capability of the modified samples were also investigated. The modified PDMS samples were examined by performing attenuated total reflection/Fourier transform infrared spectroscopy, dynamic mechanical thermal analysis, scanning electron microscopy, and water contact‐angle measurements. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 2145–2156, 2003