bluuebunny/crossref_metadata_2025 huggingface dataset:
Strategies for enhancing the adoption of school‐based prevention programs: Lessons learned from the Blueprints for Violence Prevention replications of the Life Skills Training program
Authors: Fagan Abigail A. , Mihalic Sharon
Published: April 2003

Widespread implementation of effective programs is unlikely to affect the incidence of violent crime unless there is careful attention given to the quality of implementation, including identification of the problems associated with the process of implementation and strategies for overcoming these obstacles. Here we describe the results of a process evaluation focused on discovering common implementation obstacles faced by schools implementing the Life Skills Training (LST) drug prevention program. The evaluation was conducted by the Center for the Study and Prevention of Violence (CSPV) under the Blueprints for Violence Prevention Initiative in conjunction with the designer of the LST program, Dr. Gilbert Botvin and his dissemination agency, National Health Promotion Associates (NHPA), and was funded by the Office of Juvenile Justice and Delinquency Prevention (OJJDP).

This evaluation revealed that the 70 sites involved in the project faced many obstacles when implementing this science‐based program in the “real” classroom setting, outside the rigorous controls of a research trial. Nonetheless, the schools were very successful in delivering the program in its entirety and with a high level of fidelity to the program model, and we attribute much of this success to the high level of independent monitoring provided by CSPV, as well as our ongoing efforts to work with schools to identify and overcome problems associated with implementation. © 2003 Wiley Periodicals, Inc. J Comm Psychol 31: 235–253, 2003.
Confirmatory factor analysis of the Sense of Community Index and development of a Brief SCI
Authors: Long D. Adam , Perkins Douglas D.
Published: April 2003

The Sense of Community Index (SCI) is the most widely used measure of the construct, despite the lack of confirmation of its intended dimensions or subscales. Yet psychometric appraisals of the SCI have never used the proper tool for evaluating an established dimensional construct: confirmatory factor analysis (CFA). The Block Booster Project data set (of residents of 47 street blocks in Brooklyn and Queens, New York) used in developing the original SCI in 1985 was used here in its reassessment, along with a 1‐year follow‐up survey expanded to 61 blocks. The Sense of Community Index reanalysis using CFA yielded poor model fit for McMillan and Chavis' (1986) original theoretical formulation as well as for a single‐factor index, prompting development of a Brief SCI. The eight‐item, three‐factor BSCI showed good model fit with CFA, reliable construct validity in multilevel correlational analyses, and it differentiated street block neighborhoods reliably based on intragroup agreement, while retaining the profile of a cognitive‐perceptual construct, which does not crossover with other popular community psychology constructs such as place attachment and community satisfaction. The authors, however, recommend future uses of the BSCI employ a 5‐point Likert‐type response format to increase the measure's variability, sensitivity, and internal reliability. © 2003 Wiley Periodicals, Inc. J Comm Psychol 31: 279–296, 2003.
First‐grade child risk behaviors for community violence exposure in middle school
Authors: Boyd Rhonda C. , Cooley Michele R. , Lambert Sharon F. , Ialongo Nicholas S.
Published: April 2003

This study examined behavioral indicators (measured by multiple informants) of young urban children's exposure to community violence during middle school. The community‐based school sample included 549 students (53% male; 86.8% African American, 13.2% Euro American). First‐grade aggressive behavior and anxiety symptoms were examined as predictors of later victimization and witnessing of community violence. Logistic regression analyses indicated that girls' first‐grade aggression significantly predicted witnessing violence in middle school, regardless of informant. Parent‐reported child aggression significantly predicted boys' later victimization. Teacher‐ and parent‐reported child aggression was associated with witnessing more community violence among boys with low self‐reported anxiety. Anxiety attenuated the relationship between aggression and witnessing community violence during adolescence for boys. The importance of the identifying early predictors of later community violence exposure in designing preventive interventions is discussed. © 2003 Wiley Periodicals, Inc. J Comm Psychol 31: 297–314, 2003.
Postprogram follow‐up effects of paraprofessional intervention with high‐risk women who abused alcohol and drugs during pregnancy
Authors: Grant Therese , Ernst Cara C. , Pagalilauan Genevieve , Streissguth Ann
Published: April 2003

This study examined the postprogram follow‐up status of mothers who abused alcohol and drugs heavily during a target pregnancy, were enrolled in the Parent–Child Assistance Program (PCAP), and received paraprofessional home visitation and advocacy for 3 years after delivery. Outcomes were examined across two time intervals: between program enrollment and 3‐year exit, and between 3‐year exit and postprogram follow‐up an average of 2.5 years later. At postprogram follow‐up we observed a significant increase in abstinence from alcohol and drugs for 6 months or more, and significant decreases in subsequent pregnancies and deliveries. These outcomes are of special importance because PCAP intervention efforts target behaviors that put mothers at risk for future alcohol and drug exposed births. A significant postprogram increase in living in permanent housing and a significant decrease in incarceration were other notable findings. We conclude that given specific program goals, facilitated linkages to appropriate community services, and the necessary time for gradual change to occur, supportive paraprofessional advocacy can assist many high‐risk mothers in moving toward sustained recovery and improved stability even years after intervention. © 2003 Wiley Periodicals, Inc. J Comm Psychol 31: 211–222, 2003.
Biological, social, and community influences on third‐grade reading levels of minority Head Start children: A multilevel approach
Authors: Rauh Virginia A. , Parker Faith Lamb , Garfinkel Robin S. , Perry Judy , Andrews Howard F.
Published: April 2003

The purpose of the study was to determine the impact of individual and community level risks on school outcomes of children who attend Head Start. We studied a sample of 3,693 African American and Hispanic children who had been born in New York City, participated in Head Start, and attended New York City public schools. The outcome was the score obtained on a citywide third‐grade reading test. Individual level risk factors were derived from birth certificate data. Community level risks were extracted from citywide U.S. Census data and other public‐access data sets. Multilevel regression analyses indicated that at the individual level, lower reading scores were significantly associated with: male gender, low birth weight, unmarried mother, low maternal education, and inadequate interpregnancy spacing. Controlling for individual‐level risk, concentrated community poverty significantly lowered reading scores, and a high percentage of immigrants in the community significantly raised scores. There was also a significant crosslevel effect: boys benefited more than girls from the immigrant community effect. The evidence suggests that we can better identify children at future educational risk and maximize the success of early intervention programs by exploring influences on school success at multiple levels, including the community. © 2003 Wiley Periodicals, Inc. J Comm Psychol 31: 255–278, 2003.
Feminism found: An examination of gender consciousness in community psychology
Authors: Angelique Holly L. , Culley Marci R.
Published: April 2003

Articles about women's issues published in the American Journal of Community Psychology and Journal of Community Psychology, from their inception in 1973 through 2000 were examined for feminist content. Feminism was defined as including consciousness of gender issues, gender‐stratified power imbalances, and contextual analyses of gender. We identified 89 articles with feminist content. All 89 feminist articles were examined to identify themes of gender consciousness and intersecting identities. Within the theme of gender consciousness, we identified articles that addressed power asymmetries, the link between individuals and environments, contextual analyses, and a focus on competencies. Within the theme of intersecting identities, we identified articles that addressed race, class, sexual orientation, and disabilities. We discuss the trend toward more feminist research and explore ways create a feminist subdiscipline within the field of community psychology. Finally, we discuss recommendations for future feminist scholarship in the field. © 2003 Wiley Periodicals, Inc. J Comm Psychol 31: 189–209, 2003.
The relationship among psychological distress, employment, and drug use over time in a sample of female welfare recipients
Authors: Atkinson John S. , Montoya Isaac D. , Whitsett Donna D. , Bell David C. , Nagy Carl W.
Published: April 2003

In this study we examined the relationship over time among work experience, psychological distress, and illegal substance use in a sample of 534 women receiving Temporary Assistance for Needy Families. Study participants were interviewed at intake and at 4‐month intervals for a period of 2 years. Each interview recorded the number of hours worked in the previous 4 months and the use of powder cocaine, crack cocaine, heroin, or methamphetamines during the same period. To measure the extent of psychological distress, participants were also administered the personal adjustment problems subscales of the Multidimensional Addictions and Personality Profile (MAPP) at intake and at 1‐year intervals. A path model was analyzed to assess the temporal effects of employment, drug use, and emotional and psychological distress. Results suggest a cycle in which employment at one time period can reduce the likelihood of drug use in the following period, which, in turn, can lead to improvement in distress. This improvement can lead to an increase in the number of hours worked and further improvement in distress levels. © 2003 Wiley Periodicals, Inc. J Comm Psychol 31: 223–234, 2003.
Über die Autoxydation gesättigter makromolekularer Kohlenwasserstoffe
Authors: Dulog Von L. , Radlmann E. , Kern W.
Published: April 2003

Die Autoxydation in Lösung von isotaktischem Polypropylen bzw. Polyputylen‐1 gehorcht einer anderen kinetischen Beziehung als die entsprechende Autoxydation von ataktischem Polypropylen, Polybutylen‐1 und Polyäthylen. Die Autokatalyse der Autoxydation isotaktischer Produkte wird durch einen bimolekularen Kettenstart der gebildeten Hydroperoxyde hervorgerufen, während bei ataktischen Produkten ein monomolekularer Kettenstart beobachtet wird. Die unterschiedliche Kinetik der Autoxydation kann eindeutig auf Taktizitätsunterschiede zurückgeführt werden.
Zur Beurteilung der Polydispersität von Polymeren aus Viskositätsmessungen
Authors: Breitenbach Von J. W.
Published: April 2003

Der Einfluß der Polydispersität von Polymeren auf ihr Viskositätsverhalten wird auf der Grundlage bekannter Beziehungen kurz beschrieben. Es wird gezeigt, daß, außer im Falle sehr großer Uneinheitlichkeit, die Empfindlichkeit der Viskositätsmethode für eine Beurteilung der Uneinheitlichkeit nicht ausreicht.
Structural studies on human serum gamma‐globulins and myeloma proteins. I. Fragmentation and denaturation of the globulins with detergent and alkali.
Authors: Jirgensons B. , Yonezawa D. , Gorguraki V.
Published: April 2003

The denaturation of human serum γ‐globulin and myeloma protein was studied by sedimentation, viscosity, and optical rotatory dispersion methods. Sodium decyl sulfate, in alkaline solutions of pH 10.2–11.0, was found to be very effective at sufficiently high concentrations of the detergent and higher temperatures of 50°C. The macromolecules of the globulins were inflated (or unfolded) and split into fragments having molecular weight of approximately 60,000. The optical activity measurements showed that the b0 values of the native globulins were near zero, and that they became negative on denaturation and fragmentation. The levorotation thereby increased. Upon removal of the detergent by dialysis the b0 returned to zero, while the levorotation remained strongly negative. The fragments thereby tended to aggregate, especially when the pH was decreased to near neutrality.

It was concluded that the structural changes occurred in the following steps:
(1) Native, ordered macromolecule → (2) Disorganized and fragmented macromolecule → (3) Partially organized fragments → (4) Strongly disorganized and aggregated fragments.

A tentative schematic model of the globulin macromolecule was presented in which a non‐helical order is assumed in the native state, and the detergent‐alkali fragmentation and denaturation explained as chain separation and further conformational transition of the separated subunits.
Lineare und cyclische Oligomers aus Hexamethylendiamin und Sebacinsäure
Authors: Zahn Von Helmut , Gleitsmann Günter B.
Published: April 2003

Die Oligoaminosäuren, Oligodicarbonsäuren und Oligodiamine von Nylon‐6.10‐Typ wurden jeweils bis zum Trimeren dargestellt. Die Synthese des dimeren Cycloamids c[B—Seb]2 gelang mit Hilfe der Thiophenylestermethode. Einige physikalische Eigenschaften der erhaltenen Verbindungen werden diskutiert.
Über die Vernetzungskontraktion des Polyvinylalkohol‐Cu••‐Muskels. Der E‐Modul‐Wirksamkeitsfaktor der Cu••‐Vernetzung
Authors: Kuhn Von Werner , Toth I. , Kuhn H. J.
Published: April 2003

Fäden aus Polyvinylalkohol wurden zunächst im homogenen Zustande thermisch vernetzt, so daß sie in Wasser bzw. in einem n/10 Na‐Acetatpuffer stark quellen, ohne sich zu lösen. Die gequollenen Folien wurden anschließend durch Einwirkung von Cu••‐Ionen zusätzlich vernetzt. Es tritt dabei eine Kontraktion der Folien sowie eine Erhöhung des E‐Moduls ein. Die durch Einwirkung eines Cu••‐Ions herbeigeführte Erhöhung des E‐Moduls wird verglichen mit der beispielsweise bei Kautschuk durch die Bildung eines Vernetzungspunktes herbeigeführten E‐Modul‐Erhöhung, gemessen am homogenen und am anschließend an die Vernetzung gequollenen Kautschuk.

Die Wirksamkeit je Vernetzungspunkt ist bei der Cu••‐Vernetzung des gequollenen Polyvinylalkohols etwa 6 bis 8 mal kleiner als die Wirksamkeit je Vernetzungspunkt beim homogenen Kautschuk. Das Auftreten eines E‐Modul‐Wirksamkeitsfaktors fE von der Größe 1/6 bis 1/8 bei der Cu••‐Vernetzung des gequollenen Polyvinylalkohols wird in erster Linie dadurch gedeutet, daß beim hoch gequollenen Polyvinylalkoholgel ein großer Teil des Vernetzungsreagenses für die Bildung von Netzwerkteilen mit sehr kleinem Netzbogengewicht verwendet wird. Es entsteht dann an Stelle eines homogenen ein hinsichtlich der Netzbogengewichtsverteilung stark unhomogenes Netzwerk, für welches ein stark unterhalb 1 liegender E‐Modul‐Wirksamkeitsfaktor modellmäßig zu erwarten ist.
Cyclopolymerization. III. Kinetics of polymerization and copolymerization of vinyl‐trans‐cinnamate
Authors: Roovers J. , Smets G.
Published: April 2003

The kinetics of cyclopolymerization and cyclo‐copolymerization of vinyl cinnamate were studied. The mechanism of chain propagation during the cyclopolymerization of vinyl cinnamate was considered. By determination of the residual unsaturation of the polymer (I.R. and U.V. spectrometry and bromometry) at different monomer concentrations, it was possible to evaluate the ratio of the cyclization rate constant to the vinyl propagation rate constant; it is equal to 13.

In the range of low monomer concentrations the polymerization of vinyl cinnamate is of first order with respect to monomer concentration, and of one half order with respect to initiator concentration. At monomer concentration higher than three mole·1.minus;1 the reaction becomes independent of monomer concentration, and first order with respect to the initiator.

Modified copolymer composition equations were derived taking due account of the different reactivity of the monomer radical before and after cyclization; consequently three reactivity ratios r1, r2, and r3 have been defined, and the experimental methods for their evaluation determined.

On the basis of these equations the following reactivity ratios have been evaluated: vinyl cinnamate(M1)‐vinyl acetate r3 = 1.2 ± 0.1 and r2 = 0.04; M1‐vinyl pyrrolidone r3 = 1.15–1.30 and r1 = 0.01; M1‐methacrylonitrile r3 = 0.15 and r2 = 4; M1‐styrene r1 = 0.25 ± 0.1 and r2 = 1.25 ± 0.1. The interpretation of these data suggests formation of a pseudo‐cyclic benzyl radical stabilized by resonance before addition of the second vinyl monomer.
Absolutbestimmung der Taxie des Polyvinylchlorids aus dem Ultrarotspektrum
Authors: Germar Von H. , Hellwege K.‐H. , Johnsen U.
Published: April 2003

Bei der statistischen molekularen Bewegung einer gelösten PVC‐Kette werden in der unmittelbaren Umgebung der CH2‐Gruppen vier Konformationen bevorzugt eingenommen, die dadurch ausgezeichnet sind, daß sie Gleichgewichtslagen zwischen Potentialbergen bilden. Diese energetisch ausgezeichneten Konformationen unterscheiden sich für CH2‐Gruppen an isotaktischen und syndiotaktischen Monomerverkettungen. Die dadurch entstehenden verschiedenen molekularen Umgebungen der Methylen‐Gruppe im PVC geben den CH2‐Scherenschwingungen eine andere Frequenz. Während die beiden möglichen isotaktischen Konformationen als Spiegelbilder energetisch gleichwertig sind, so daß in ihnen die Scherenschwingung bei einer Frequenz, nämlich bei 1434 cm−1 absorbiert, verteilen sich die beiden energetisch unterschiedlichen Konformationen der syndiotaktischen Segmente gemäß einem BOLTZMANN‐Gleichgewicht auf die beiden Banden bei 1428 und 1434 cm−1. Durch Messung der Temperaturabhängigkeit des Intensitätsverhältnisses dieser Banden in PVC‐Lösungen ist es daher möglich, den syndiotaktischen Anteil α des PVC und die Energiedifferenz ΔE zwischen den beiden syndiotaktischen Anordnungen nach folgender Formel zu bestimmen:

Hierbei ist λ das Verhältnis der optischen Dichten der beiden Banden, d. h.

Für die sechs untersuchten PVC‐Proben, die zwischen +30 und −70°C polymerisiert worden waren, steigen die α‐Werte von 0,5 auf 0,8. Die zugehörigen Energiedifferenzen ΔE liegen bei den Proben mit α > 0,7 einheitlich bei 840 cal/Mol, während für die zunehmend ataktischen Proben mit α zwischen 0,5 und 0,6 die Energie auf 1360 bzw. 1920 cal/Mol ansteigt.
Moleküldimensionen und 2. Virialkoeffizient von Polystyrol in 8 Thetalösungsmitteln
Authors: Schulz Von G. V. , Baumann H.
Published: April 2003

Im Temperaturbereich zwischen −10 und +130°C werden Lichtstreuungs‐ und Viskositätsmessungen an einer Polystyrolfraktion (Mw = 170 000) in 8 Lösungsmitteln vorgenommen, deren Thetatemperaturen zwischen −9 und +83°C liegen. In 7 Lösungsmitteln ist [η]Θ und damit der Trägheitsradius rΘ von der Temperatur und vom Lösungsmittel nur wenig abhängig; in Cyclohexanol besteht eine größere Abweichung. Aus dem Gang des 2. Virialkoeffizienten mit der Temperatur kann die h(z)‐Funktion berechnet werden. Sie gehorcht ziemlich genau den Gleichungen von ISIHARA‐KOYAMA bzw. OROFINO‐FLORY.
Über 2‐vinylthianthren und seine Polymerisationsprodukte
Authors: Hopff Von H. , Gutenberg H.
Published: April 2003

Das bisher unbekannte 2‐Vinylthianthren wurde durch Acetylierung von Thianthren, Reduktion des Ketons zum Carbinol, Veresterung mit Essigsäure und Pyrolyse des Acetyl‐Derivats hergestellt und seine Polymerisation und Copolymerisation mit Methylmethacrylat, äthylacrylat und Styrol untersucht.
Über die ionische Polymerisation von Acrolein und die Struktur der Polymerisate. Polymere Acroleine. 27. Mitt.
Authors: Schulz Von Rolf C. , Passmann Wolfram
Published: April 2003

Die Polymerisation von besonders gereinigtem Acrolein mit verschiedenen anionischen Katalysatoren sowie mit Borfluoridätherat wird beschrieben. Diese Polymerisate haben andere physikalische und chemische Eigenschaften als die mit Redoxsystemen gewonnenen Polyacroleine. Es wurden Polymere hergestellt, die nur etwa 2 Mol‐% Aldehydgruppen enthalten, aber 70 Mol‐% Doppelbindungen. Durch spektroskopische und chemische Methoden konnte die Struktur dieser Polymeren weitgehend aufgeklärt werden.
Der Nachweis der Kettenstruktur von aus p‐Kresol und Formaldehyd aufgebauten Mehrkernverbindungen. II. Umsetzungen an den phenolischen Hydroxygruppen, zusammen mit kettenanalogen Reaktionen
Authors: Kämmerer Von Hermann , Schweikert Heinz
Published: April 2003

Die Kettenstruktur von 2,2′‐Dihydroxy‐5,5′‐dimethyl‐diphenylmethan (I), 2,6‐Bis‐(2‐hydroxy‐5‐methyl‐benzyl)‐4‐methylphenol (II) und 3,3′‐Bis‐(2‐hydroxy‐5‐methyl‐benzyl)‐2,2′‐dihydroxy‐5,5′‐dimethyl‐diphenylmethan (III) wird bewiesen durch quantitative Acylierungen in Verbindung mit einer hydrierenden Enthalogenierung6 der Dihalogenverbindungen von I, II und III (V, VI und VII). Der Beweis wird durch quantitative Acylierungen sowie Umsetzung der Enthalogenierungsprodukte zu Bis‐(dimethyl‐aminomethyl)‐mehrkernverbindungen vervollständigt.
Polyoxymethylene from trioxane by solid state polymerization: A case of twinning in a synthetic polymer
Authors: Carazzolo G. , Leghissa S. , Mammi M.
Published: April 2003

The products obtained by sublimation or radiation of trioxane byhigh energy radiations have been examined by X‐ray diffraction analysis.

It have been possible to demonstrate that they consist of twinned crystals of hexagonal polyoxymethylene. By using rotating and WEISSENBERG photographs, the geometric correlations between the elements of the twins were also definitely established.
Contribution of the internal energy to the retractive force of vulcanized cis‐1,4 polybutadiene
Authors: Crespi G. , Flisi U.
Published: April 2003

The stress‐temperature coefficients were determined at different extension ratios for samples of vulcanized cis‐1,4‐polybutadiene with two different cross‐linking degrees. The contribution of the internal energy to the total stress was deduced from the values obtained.

By extrapolating the data obtained, the dependence in respect to temperature of the mean square length was obtained by three different methods, and values coincident among themselves were obtained.

Also the ε′ value for the equivalent “ε′ folding chain” was calculated. Finally the dependence of \documentclass{article}\pagestyle{empty}\begin{document}$ \frac{{{\rm d ln \bar r}_{\rm 0} ^{\rm 2} }}{{{\rm dT}}} $\end{document} on temperature and on the extension ratio was studied.
Preparation and crystal structure of isotactic poly(vinyl tert. Butyl ether)
Authors: Bassi I. W. , Dall'Asta G. , Campigli U. , Strepparola E.
Published: April 2003

Some “modified FRIEDEL‐CRAFTS” catalysts were studied in the cationic polymerization of the vinyl tert butyl ether in the homogeneous phase. The highest stereospecificity is obtained in the case of boron containing compounds, like boron monoalkyl difluorides. This fact is explained with the higher possibility of these compounds to form co‐ordination complexes with the monomer.

Some properties of the poly(vinyl tert‐butyl ethers) having high degree of crystallinity are described. The X‐ray examination of oriented fibres of the polymer allows to establish that the macromolecular chains assume in the lattice the conformation of a four‐fold helix. The space group and the lattice constants of the tetragonal unit cell of the polymer are defined.
Stereospecific polymerization of perfluoroolefins
Authors: Sianesi Dario , Caporiccio Gerardo
Published: April 2003

Preliminary results of research work in the field of stereospecific polymerization of fluorine‐containing olefins are reported. It is shown for the first time that ZIEGLER‐NATTA type catalysts may be used for polymerizing fully fluorinated olefins. By employing catalysts based on titanium tetraalcoholates and alkylaluminum derivatives, in halogenated solvents, slow conversion to crystalline polymers was obtained from tetrafluoroethylene and hexafluoropropylene. To the new crystalline polyhexafluoropropylene, whose main properties are described, an isotactic structure can probably be assigned. Some features of the stereospecific polymerization of perfluoroolefins are reported and briefly discussed.
Frequency shifts in the infrared spectrum of human deoxyribonucleic acid
Authors: Zerbi Giuseppe , Bianchi Paolo , Polli Elio E.
Published: April 2003

The infrared spectra of DNA from calf thymus, human normal and human leukaemic leucocytes was recorded in solution of H2O and D2O. Spectra have been also obtained after the samples in D2O have been subjected to the following treatments: heating, acid and enzymatic hydrolysis. The spectrum of apurinic acid has been determined. A detailed study is carried out in the frequency region from 1750 to 1550 cm−1 with improved resolution. The experimental difficulties for recording the spectrum in this spectral range are discussed. In disagreement with previous works it was found that the pair of strong bands at 1645 and 1680 cm−1 in the spectrum of the starting material shifts to 1660 and 1690 cm−1 respectively along with changes in intensity after treatment. Assignments of the bands in the same frequency range are tentatively proposed and the frequency shifts are explained in terms of the intermolecular interaction between purine and pyrimidine units. An infrared criterion for the existence of the double‐stranded helix is postulated as follows: the pair of infrared bands at 1645 and 1680 cm−1 characterizes a regular double‐stranded helix; a strong band at 1660 cm−1 and a weaker one at 1690 cm−1 indicate a deformed or denaturated DNA.
Cyclic Polymers by Kinetically Controlled Step‐Growth Polymerization
Authors: Kricheldorf Hans R. , Schwarz Gert
Published: April 2003

The theory of step‐growth polymerizations including the cascade theory is discussed in the light of new results focussing on the role of cyclization reactions. The identification of cyclic oligomers and polymers in reaction products of step‐growth polymerizations has been eased considerably by means of MALDI‐TOF mass spectrometry. Experimental examples concern syntheses of polyesters, polycarbonates, polyamides, polyimides, poly(ether sulfone)s, poly(ether ketone)s and polyurethanes. It was found in all cases that the percentage and molecular weight of the cycles increases when the reaction conditions favor high molecular weights. In the absence of side reactions all reaction products will be cycles when conversion approaches 100%. Cyclization may even take place in the nematic phase but even‐numbered cycles are favored over odd‐numbered ones due to electronic interactions between mesogens aligned in parallel. In contrast to Flory's cascade theory, cyclization also plays a decisive role in polycondensations of abn‐type monomers, and at 100% conversion all hyperbranched polymers have a cyclic core. Furthermore, it is demonstrated that in a2+b3 polycondensations intensive cyclization in the early stages of the process has the consequence that either no gelation occurs or the resulting networks consist of cyclic and bicyclic oligomers as building blocks. Finally, a comparison between cyclization of synthetic polymers and biopolymers is discussed.

Schematic representation of a network structure mainly consisting of cyclic oligomers and multicyclic building blocks as derived from “a2” + “b3” polycondensation.

magnified image

Schematic representation of a network structure mainly consisting of cyclic oligomers and multicyclic building blocks as derived from “a2” + “b3” polycondensation.
Transition in swollen polymer networks induced by intramolecular condensation
Authors: Dušek K. , Patterson D.
Published: April 2003

It is predicted that the net repulsion between the segments of a polymer network and a poor solvent can cause a phase transition marked by a sudden change in the degree of swelling. This is analogous to the “coil–globule” transition recently predicted by Ptitsyn to occur for a macromolecule in solution. The critical conditions for the transition. as well as phase diagrams, are calculated for the gel in free swelling and under uniaxial tension, which facilitates the transition. The transition depends on the gel being formed of chains crosslinked while greatly swollen by a diluent and also having a high degree of crosslinking. It is concluded that it would be difficult to attain the conditions necessary for the transition in the free‐swelling case, but that it should be possible for gel under tension.
Role of diffusion in gel permeation chromatography
Authors: Hermans J. J.
Published: April 2003

A theory is developed that describes the diffusion of solute into the gel particles during a gel permeation chromatographic experiment. The particles are treated as homogeneous spheres of radius a, into which diffusion takes place with diffusion coefficient Ds. The concentration in the mobile phase at any level at any time is supposed to be uniform throughout the cross‐section of the column. It is shown that in the usual columns the effect of diffusion in the mobile phase is unimportant. A determinative quantity in the process is the parameter a2/Dst, where t is the time. For large values of a2/Dst an explicit expression for concentration versus time in the mobile phase at the end of the column is derived [eq. (26) and Fig. 1]. It shows a relatively long tail at large efflux volumes V, where the concentration varies at V−3/2. For arbitrary values of a2/Dst the first three moments of the concentration versus time curve are calculated [eqs. (33)–(37)]. Pronounced skewness of the curve is found unless a2/Dst is small.
Second virial coefficient of polymers in good solvents: The case of polyelectrolytes
Authors: Alexandrowicz Z.
Published: April 2003

A stepwise segment‐by‐segment cluster development of the interaction energy of two polymer coils at given distance leads to a closed expression, describing the second virial coefficient A2 in terms of certain intersegmental contact probabilities. An approximate expression for A2(α,z) in good solvents is then derived by using the uniform segment cloud model; the result being equivalent to that obtained by Flory. This expression is combined with the author's theory for α2(z) to give A2(z), and then with a subsequent adaptation of that theory to polyelectrolytes, to derive the dependence of A2 on ionic strength. The α2(z) and A2(z) equations are both compared with recently reported experimental data for NaPSS.
Temporary changes in electrical properties of polymer dielectrics due to ionizing radiation
Authors: Adamec V.
Published: April 2003

Measurements of conductivity, permittivity, and dissipation factor on polystyrene, low‐density polyethylene, poly(ethylene terephthalate), and polytetrafluoroethylene under irradiation with x‐rays at exposure rates from 0.004 to 400 r/sec. are presented. The radiation‐induced anomalous conductivity as well as the induced dielectric loss are interpreted by Maxwell‐Wagner polarization due to radiation imbalance in surface layers of the specimen. The nature of radiation‐induced steady‐state conductivity is also discussed.
Morphology of polypropylene crystals. III. Lamellar crystals of thermally decomposed polypropylene
Authors: Kojima Morio
Published: April 2003

Morphology and crystal structure of solution‐grown and melt‐grown crystals of thermally decomposed polypropylene have been studied by electron microscopy and x‐ray diffraction. By crystallization from dilute α‐chloronaphthalene or carbitol solutions well‐defined lamellar crystals about 100–150 A. in thickness are obtained from fractions (number‐average molecular weights 1600–2100) of thermally decomposed crystalline polypropylene. The structure is monoclinic as crystallized from very dilute α‐chloronaphthalene or carbitol solutions (0.02–0.005 wt.‐%). However crystals of the triclinic as well as of the monoclinic forms are precipitated from carbitol solutions of higher concentrations (0.05‐1 wt.‐%). On the other hand, the separated triclinic form has been obtained from the melt. Crystals of both modifications have similar morphology. In addition, the chain molecules cannot be expected to fold, within the thickness of lamellae in crystals of either modification prepared from the low molecular weight fractions used in this study.
Small‐angle x‐ray diffraction studies of plastically deformed polyethylene. II. Influence of draw temperature, draw ratio, annealing temperature, and time
Authors: Peterlin A. , Corneliussen R.
Published: April 2003

The angular dependence of scattering intensity of drawn polyethylene (PE) was investigated with a small‐angle Kratky camera. At constant drawing temperature the intensity drops drastically with increasing draw ratio; however, the position and the half‐width of the first maximum remain nearly unchanged. The drop in intensity can be explained only by a reduction of effective electron density difference between amorphous and crystalline components. The latter contains more vacancies, and the former contains more and better packed tie molecules. This increases the average density of the amorphous layer and decreases that of the crystalline component. As the temperature of the drawing increases, the draw ratio attainable at the applied draw rate drops and the intensity of scattering and the long period rapidly increase. In addition, a second‐order maximum appears, indicating a better order of lamellar stacking, in good agreement with electron microscopy. The first annealing effect is an extremely rapid increase in scattering intensity and long period. The subsequent increase is rather slow and proportional to the logarithm of annealing time. The long period in such an experiment is independent of the draw ratio; however, the scattering intensity depends on it quite strongly even after prolonged annealing.
Thermoluminescence in poly(methyl methacrylate) γ‐irradiated at 77°K
Authors: Fleming R. J.
Published: April 2003

Isotactic and atactic poly(methyl methacrylate) containing varying amounts of polymerization initiator and chain‐transfer additives, and carefully purified radiation‐polymerized material, were γ‐irradiated in the dark at liquid nitrogen temperature. On warming to room temperature at a near‐linear rate of 20°K./min., a glow peak having a maximum luminescence intensity at 162 ± 8°K. was observed in all samples; an additional peak at 239 ± 7°K. was resolved relatively infrequently. Low luminescence yields precluded an investigation of the spectral distribution of the glow peaks. It is shown that the electron traps associated with the lower temperature peak are most probably the main‐chain methyl groups, while the higher temperature glow peak is tentatively associated with escape of electrons from structural defects in a few small crystalline regions of the samples. It is postulated that, for the peak at 162°K., the trapped electrons combine radiatively with luminescence centers when thermally induced rotational motion of the main‐chain methyl groups permits sufficient wave‐function overlap. Assuming that methods of glow curve analysis proposed for inorganic materials are applicable to organics, first‐order recombination kinetics and an activation energy of 0.084 ± 0.006 e. v. are deduced for the intensity maximum at 162°K. This activation energy is in fair agreement with that obtained by Bordoni et al. for an unspecified side‐chain motion occurring at similar temperatures, but is only about half the values quoted with some reservations by Powles and by Kawai on the basis of NMR experiments. It was not possible to determine the kinetics of the 239°K. peak with certainty, but an activation energy of 0.432 ± 0.085 e. v. follows from a first‐order assumption. The additives present in the samples did not appear to play any significant part as electrontrapping agents; this observation contrasts with some recent work on the visible and ultraviolet absorption spectra of the same materials which showed a close correlation of additional bands developed following irradiation with the presence of specific additives.
Dielectric relaxation and electrical conduction of polymers as a function of pressure and temperature
Authors: Saito Shogo , Sasabe Hiroyuki , Nakajima Tatsuji , Yada Koji
Published: April 2003

The dielectric properties and the d. c. conductivity of poly(vinyl chloride), poly(vinyl acetate), polychlorotrifluoroethylene, and poly(ethylene terephthalate) were measured at temperatures above and below the glass transition temperature and at various pressures up to 3000 atm. The α relaxation associated with the micro‐Brownian motion of amorphous chain segments depends strongly upon temperatures and pressure, while the β relaxation due to local‐mode motion of the frozen main chain shows weak dependence on temperature and pressure. It is found that the free volume concept is valid for description of the temperature and the pressure dependence of the relaxation time for the α process. Activation energy and volume for both relaxation processes are determined from the experimental data. A simple relation between activation energy and volume for the α relaxation and pressure dependence of the glass transition temperature are derived. Temperature and pressure dependence of the d. c. conductivity in the rubbery state are notably different from those in the glassy state. Ionic conduction appears to be dominant in these polymers.
Effects of temperature and water on the γ → α crystalline transition of nylon 6 caused by stretching in the chain direction
Authors: Miyasaka Keizo , Ishikawa Kinzo
Published: April 2003

The effects of temperature and water on the crystal transition of nylon 6 from the γ phase to the α phase, which is caused by stretching along the chain direction, were investigated. The γ‐phase fibers with high crystallite orientation were stretched at constant load under various conditions. An inversion of the effect of water on the transition occurs at about −60°C. Stretching in the wet state is more effective for the transition at higher temperature. In contrast, at low temperatures water in the crystalline regions actsasa cohesive agent for the chains and increases the activation energy for the transition. Thus, dry stretching is more effective than wet stretching at very low temperature. The fraction of transformed α‐phase crystallites increases abruptly over a narrow range of stress. Thus the critical stress can be determined for the transition. The critical stress changes appreciably with temperature; the higher the temperature, the lower the critical stress. The relation between stretching temperature and critical stress was analyzed by Flory's equation for the shift of transition temperature by stress. About 220°C. was estimated as the zero‐stress transition temperature. The heat content of the γ‐phase crystal was estimated to be smaller by 500 cal./mole than that of the α‐phase crystal. This result suggests that the free energy of the γ‐phase crystal is lower than that of the α‐phase crystal at temperatures lower than the transition point. The irreversible strain of a sample in which the crystal transition has taken place is very small at low temperature. This small extension of the sample is evidence that the γ → α transition produced by stretching along the chain axis is a crystal‐crystal transition.
Relaxation characteristics and intrinsic birefringence and viscosity of polystyrene solutions for a wide range of molecular weights
Authors: Thurston G. B. , Schrag J. L.
Published: April 2003

A comparison is made between measurements on polystyrene solutions and the relaxation characteristics and intrinsic birefringence and viscosity given by the theory for the flexible Gaussian chain of variable number of segments and with internal viscosity and internal hydrodynamic interaction. This is done in order to determine the applicability of the theory to polymers over a wide range of molecular weights, including the low molecular weight range in which there may be conflict with the theoretical assumption of chains having a large number of segments. The longest, terminal relaxation time and the number of chain segments are determined from measurements of the frequency dependence of oscillatory flow birefringence while the intrinsic birefringence and viscosity are determined from steady flow measurements. The range of molecular weights studied is from approximately 900 at 106. It is found that the segment weight is approximately 1000 and the number of segments is in direct proportion to the molecular weight for the range from 1 to 1000 segments. The terminal relaxation time has a molecular weight dependence of the type given by the theory but with better agreement for higher molecular weights. While the measured dependences of the intrinsic viscosity and birefringence are in agreement with theory for molecular weights greater than 5 × 104, they deviate significantly for molecular weights below 1 × 104. The ratio of the intrinsic birefringence to intrinsic viscosity, which in theory is a constant independent of molecular weight, is found to change at the lower molecular weights.
Flow‐rate dependence of gel permeation chromatography
Authors: Yau W. W. , Suchan H. L. , Malone C. P.
Published: April 2003

Analysis of polystyrene standards by gel permeation chromatography over a wide range of flow rates revealed two sources of error in volume measurement. These errors arise from solvent evaporation in the siphon chamber and from solvent continuing to flow into the siphon during discharge. Appropriate corrections are discussed, and a vapor feedback loop to eliminate the solvent evaporation error is described. The flow rate dependence of the GPC calibration curve, expressed in the corrected elution volumes, appears different from that reported in the literature. The corrected flow rate dependence of peak elution volumes is in agreement with the expectation of diffusion and exclusion theories.
Calibration procedure for gel permeation chromatography
Authors: Frank F. C. , Ward I. M. , Williams T.
Published: April 2003

A novel procedure is presented for calibrating a gel permeation chromatograph by using broad polymer fractions. The limit in accuracy is set by the accuracy of number‐average and weight‐average molecular weight measurements and the reproducibility of the chromatograph. In the particular calibration for linear polyethylene described here, low molecular weight fractions were prepared by nitric acid oxidation of annealed single crystals. The calibration is then of particular value in morphological studies of polyethylene. The influence in the calibration of polar endgroups on the polymer, as produced in these oxidized samples is discussed.
Low‐frequency losses in rubbers cross‐linked in the presence of diluent
Authors: Langley Neal R. , Dickie Ray A. , Wong Chu‐Ping , Ferry John D. , Chasset R. , Thirion P.
Published: April 2003

Measurements of the complex shear compliance have been made from 0.1 to 7 cycles/sec. and from −5° to 45°C. on several samples of natural rubber cross‐linked by dicumyl peroxide in the presence of a diluent oil (volume fraction of rubber, v2, = 0.63 and 0.76) which was subsequently extracted. The properties of the extracted vulcanizates were compared with those having the oil still present and with those of conventional undiluted vulcanizates. Measurements of the diffusion coefficient of radioactively tagged n‐hexadecane in trace amounts through the polymer structure were also made both before and after extraction of the oil. The diffusion coefficient was higher in the presence of the oil by an amount consistent with the Fujita theory for concentration dependence of diffusion rate based on free volume considerations. The low‐frequency mechanical losses (reduced to 25°C. by the method of reduced variables), as measured by the loss tangent, were shifted to higher frequencies by the presence of oil to a much larger degree than would be expected from the difference in local mobility gauged by the diffusion coefficient. The equilibrium modulus, derived by extrapolation to zero frequency, was diminished by the presence of oil to a greater extent than the factor of v2⅓ expected from the simple theory of rubberlike elasticity. The low‐frequency losses in the extracted vulcanizates were smaller than those in conventional vulcanizates with comparable degrees of cross‐linking; the differences are attributed to differences in network topology.
Growth and drawing of polyacrylonitrile crystals grown from solution
Authors: Klement J. J. , Geil P. H.
Published: April 2003

Polyacrylonitrile crystals were grown from dilute solutions of propylene carbonate by a technique similar to that described by Holland et al. Crystals were also grown on various substrates and sampled at various stages of growth after washing away the uncrystallized solution. The initial single lamellae rapidly develop into complex twinned structures with many overgrowths. The morphology of the full‐grown crystal varied considerably with crystallization temperature. Small‐angle x‐ray and electron microscopy results indicate only a small change in lamellar thickness with crystallization temperature for our polymer. Electron and x‐ray diffraction results indicate lateral order can be quite good in these crystals. Our x‐ray results indicate that the previously reported a and b parameters should be doubled to give a = 21.18 Å and b = 11.60 Å. However, there was no evidence for chain‐axis order. The crystals were stretched at various stages of growth on Mylar film. Multilamellar crystals having their long axis parallel to the draw direction formed large cracks perpendicular to the long axis. Fibers of large diameter (100–250 Å) were observed across these cracks. When the long axis of these crystals was at an angle to the draw direction no large cracks or fibers were observed. Single lamellae generally cracked perpendicular to the draw direction, irrespective of their orientation to the draw direction. Definite fibers were not observable across cracks in single lamellae.
Design of beams and beam columns
Authors: Lindner J
Published: April 2003

Beams and beam columns are very important elements in steel structures. This paper gives an introduction to mathematical solution methods, to the typical behaviour of these elements and to the design methods used in new codes in Europe. Special attention is given to the checking of cross‐sectional capacity and to the use of simplified design formulae. Additional information, such as diagrams for the lateral torsional buckling parameter k will help to solve practical design problems. For the case of lateral torsional buckling, different types of constructional details are discussed with regard to the load‐carrying capacity of beams and beam columns. The new European rules for interaction equations which are of great importance for practical design, are explained in detail, distinguishing between members which are susceptible to torsional deformations or not. Copyright © 2003 John Wiley & Sons, Ltd.
Stability of multielectron bubbles against single‐electron split‐off
Authors: Silvera I. F. , Blanchfield J. , Tempere J.
Published: April 2003

Recently, the stability of multielectron bubbles against fissioning into two fragments with large numbers of electrons each was investigated by J. T. Devreese and two of the present authors (I. S. and J. T). In the present work we study a decay mechanism not included in the earlier model on bubble stability: splitting off of single electrons from the multielectron bubble. We find that bubbles with more than a critical number of electrons are stable against this type of decay. The pressure dependence of this critical number was studied. We find that this particular decay mechanism reveals a similar pressure dependence to other decay mechanisms such as shape instabilities in that increasing the pressure destabilizes the bubble whereas a negative pressure increases bubble stability.