bluuebunny/crossref_metadata_2025 huggingface dataset:
Effective polyethylenimine‐mediated gene transfer into human endothelial cells
Authors: Zaric Violeta , Weltin Denis , Erbacher Patrick , Remy Jean‐Serge , Behr Jean‐Paul , Stephan Dominique
Published: February 2004

Background

The major advantage in choosing non‐viral vectors such as cationic polymers for in vitro and in vivo transfection is their higher biosafety than viral ones. Among the cationic polymers, polyethylenimines (PEIs) are promising molecules for gene delivery to a variety of cells. Efficient transfection of primary endothelial cells using PEIs could be regarded as an interesting strategy of treatment in some ischemic cardiovascular diseases.

Methods

Efficacies of a 22‐kDa linear PEI (L‐PEI) and its glucose‐grafted derivative (L‐PEI‐Glc4) were compared for gene transfer into human umbilical vein endothelial cells (HUVEC) using the reporter gene luciferase. Cells were incubated for 2, 4 and 24 h with PEI/DNA complexes made in 150 mM sodium chloride (NaCl) or in 5% glucose solution. Luciferase activity was measured 24 h after the onset of transfection. The effects of low (2%) and high (30%) concentrations of serum on transfection efficacy were assessed as well. We then studied the intracellular fate of the PEI/DNA complexes labelled with the DNA intercalator YOYO‐1 using flow cytometry analysis (FACS) and confocal microscopy.

Results

PEI/DNA complexes formed in NaCl led to a higher transfection efficacy than those made in glucose. The optimal formulation, depending on the incubation time and the presence of serum in the medium, was obtained using DNA complexed to L‐PEI‐Glc4 and incubated for 4 h with the cells. This condition led to 50% fluorescent cells after GFP transfection. A high serum concentration diminished the L‐PEI associated toxicity but decreased L‐PEI‐Glc4 transfection efficiency. FACS analysis using both vectors showed that almost 90% of the cells had internalized the DNA complexes. Confocal microscopic observations showed a fast attachment of the complexes to the cell surface followed by inclusion into vesicles that migrated to the perinuclear region.

Conclusions

In this work, we defined the optimal conditions for gene delivery in HUVEC. These conditions were obtained when using derivatives L‐PEI and L‐PEI‐Glc4 complexed with DNA in 150 mM NaCl and added to cells for 2 and 4 h, respectively. Cellular trafficking of the complexes suggested that cell entry was not a limiting factor for gene delivery using PEI. This study underlined the interest in PEIs as efficient vectors for gene transfer into human endothelial cells. Copyright © 2004 John Wiley & Sons, Ltd.
Post‐secretion neutralization of transgene‐derived effect: soluble erythropoietin receptor/IgG1Fc expressed in liver neutralizes erythropoietin produced in muscle
Authors: Maruyama H. , Higuchi M. , Higuchi N. , Kameda S. , Saito M. , Sugawa M. , Matsuzaki J. , Neichi T. , Yokoyama S. , Miyazaki Y. , Miyazaki J. , Gejyo F.
Published: February 2004

Background

The regulation of transgene expression is a key issue for the development of safe gene therapy. Various strategies have been used to regulate protein production at the levels of transgene expression, transcription, translation, and secretion. Neutralization following secretion is another important backup system to prevent super‐therapeutic levels of a protein from being expressed by gene transfer.

Methods

We tested whether the soluble human erythropoietin receptor (EpoR)/IgG1Fc could neutralize the rat Epo at the post‐secretory level and suppress erythrocytosis.

Results

To assess whether soluble human EpoR could bind rat Epo in vitro, we used the Epo‐dependent human leukemic cell line, AS‐E2. EpoR/IgG1Fc significantly inhibited the growth of AS‐E2 cells in Epo‐containing medium. To test this neutralization effect of EpoR/IgG1Fc in vivo, we first transferred pCAGGS‐Epo into rat muscle by in vivo electroporation, confirmed erythropoiesis for 3 weeks, and then delivered EpoR/IgG1Fc by liver‐targeted gene transfer via tail‐vein injection with hydrodynamics‐based transfection. Reticulocyte counts and hematocrit levels in rats that received pCAGGS‐EpoR/IgG1Fc injections were significantly lower than in rats that received pCAGGS‐EpoR, pCAGGS‐IgG1Fc, or no injection.

Conclusions

These results demonstrate that liver‐targeted pCAGGS‐EpoR/IgG1Fc transfer by tail‐vein injection with hydrodynamics‐based transfection is useful for neutralizing Epo delivered by in vivo electroporation. This backup strategy at the level of post‐secretion could facilitate the clinical application of gene therapy in the future. Copyright © 2004 John Wiley & Sons, Ltd.
Overexpression of human fibroblast growth factor 2 stimulates cell proliferation in an ex vivo model of articular chondrocyte transplantation
Authors: Madry Henning , Emkey Greg , Zurakowski David , Trippel Stephen B
Published: February 2004

Background

Genetically engineered chondrocytes could be used to enhance cartilage repair. Fibroblast growth factor 2 (FGF‐2) is a mitogen for chondrocytes and may be a candidate for gene transfer approaches to stimulate chondrocyte proliferation. In the present study, we tested the hypothesis that human FGF‐2 (hFGF‐2) gene transfer into articular chondrocytes modulates cell proliferation in an ex vivo model of chondrocyte transplantation.

Methods

Transfection of articular chondrocytes with an expression plasmid vector carrying the cDNA for hFGF‐2 under the control of the cytomegalovirus promoter/enhancer mediated transgene expression and synthesis of biologically relevant amounts of the recombinant hFGF‐2 protein. Articular chondrocytes transfected with the Escherichia coli β‐galactosidase (lacZ) gene or a hFGF‐2 cDNA were transplanted onto the surface of articular cartilage explants.

Results

The tissue formed by the chondrocytes expressing hFGF‐2 was thicker and contained more cells than control cultures. Quantitative analysis of [3H]thymidine and [35S]sulfate incorporation in composite cultures revealed that hFGF‐2 transfection stimulated mitogenic activity in the new tissue but did not augment matrix glycosaminoglycan synthesis.

Conclusions

These data support the concept that chondrocytes overexpressing a hFGF‐2 cDNA selectively modulate cell proliferation in an ex vivo model of chondrocyte transplantation. These results suggest that therapeutic hFGF‐2 gene transfer may be applicable for the treatment of articular cartilage disorders, such as traumatic defects in which cellular repopulation is a therapeutic goal. Copyright © 2004 John Wiley & Sons, Ltd.
Protection and selection for gene therapy in the hematopoietic system
Authors: Milsom Michael D. , Fairbairn Leslie J.
Published: February 2004

Hematopoietic stem cell gene therapy is potentially curative for a number of inherited and acquired disorders. However, poor gene transfer and expression in repopulating hematopoietic stem cells attenuate this potential. Here we review potential means of conferring a selective advantage to hematopoietic stem cells and their progeny, and discuss the issues that surround the use of selective advantages in vivo. Copyright © 2004 John Wiley & Sons, Ltd.
Cycloheximide and actinomycin D delay death and affect bcl‐2, bax, and Ice gene expression in astrocytes under in vitro ischemia
Authors: Yu Albert Cheung Hoi , Yung Hon Wa , Hui Michael Hung Kit , Lau Lok Ting , Chen Xiao Qian , Collins Richard A.
Published: February 2004

An in vitro ischemia model was established and the effect of the metabolic inhibitors cycloheximide (CHX) and actinomycin D (ActD) on apoptosis in astrocytes under ischemia studied. CHX decreased by 75% the number of cells dying after 6 hr of ischemia compared with control cultures. TdT‐mediated dUTP nick end labelling (TUNEL) staining of comparable cultures was reduced by 40%. ActD decreased cell death by 60% compared with controls. The number of TUNEL‐positive cells was reduced by 38%. The nuclear shrinkage in TUNEL‐positive astrocytes in control cultures did not occur in ActD‐treated astrocytes, indicating that nuclear shrinkage and DNA fragmentation during apoptosis are two unrelated processes. Expression of bcl‐2 (α and β), bax, and Ice in astrocytes under similar ischemic conditions, as measured by quantitative reverse transcription‐polymerase chain reaction, indicated that ischemia down‐regulated bcl‐2 (α and β) and bax. Ice was initially down‐regulated from 0 to 4 hr, before returning to control levels after 8 hr of ischemia. ActD decreased the expression of these genes. CHX reduced the expression of bcl‐2 (α and β) but increased bax and Ice expression. It is hypothesized that the balance of proapoptotic (Bad, Bax) and antiapoptotic (Bcl‐2, Bcl‐Xl) proteins determines apoptosis. The data suggest that the ratio of Bcl‐2/Bad in astrocytes following ActD and CHX treatment does not decrease as much in untreated cells during ischemia. Our data indicate that it is the ratio of Bcl‐2 family members that plays a critical role in determining ischemia‐induced apoptosis. It is also important to note that ischemia‐induced apoptosis involves the regulation of RNA and protein synthesis. © 2003 Wiley‐Liss, Inc.
Widely expressed transcripts for chemokine receptor CXCR1 in identified glutamatergic, γ‐aminobutyric acidergic, and cholinergic neurons and astrocytes of the rat brain: A single‐cell reverse transcription‐multiplex polymerase chain reaction study
Authors: Danik M. , Puma C. , Quirion R. , Williams S.
Published: February 2004

Increasing evidence suggests that the chemokine interleukin (IL)‐8/CXCL8 plays important roles in CNS development, neuronal survival, modulation of excitability, and neuroimmune response. Recently, we have shown that CXCL8 can acutely modulate ion channel activity in septal neurons expressing receptors CXCR1 and/or CXCR2. This was a surprising finding, insofar as CXCR1 expression had not been described for the mammalian brain. Here we investigated whether CXCR1 transcripts are present in other brain regions, whether they are expressed at the single‐cell level in molecularly identified neurons and astrocytes, and how they are regulated during early postnatal development. In addition, possible cellular colocalization of CXCR1 and CXCR2 transcripts was examined. Semiquantitative reverse transcription‐polymerase chain reaction (RT‐PCR) revealed that CXCR1 mRNAs were expressed in the septum, striatum, hippocampus, cerebellum, and cortex (temporoparietal and entorhinal) at different levels and appeared to be regulated independently from CXCR2 during development. By using RT multiplex PCR on acutely dissociated cells from these brain regions, we show that CXCR1 transcripts were expressed in 83% of 84 sampled neurons displaying cholinergic (choline acetyltransferase mRNAs), γ‐aminobutyric acidergic (glutamic acid decarboxylases 65 and 67 mRNAs), or glutamatergic (vesicular glutamate transporters 1 and 2 mRNAs) phenotypes. CXCR1 and CXCR2 transcripts were colocalized in 45% of neurons sampled and also were present in some glial fibrillary acidic protein mRNA‐expressing astrocytes. This is the first study to demonstrate the widespread expression of CXCR1 transcripts in the brain and suggests that CXCR1 may have hitherto unsuspected roles in neuromodulation and inflammation. © 2003 Wiley‐Liss, Inc.
Inhibition of α‐ketoglutarate dehydrogenase complex promotes cytochrome c release from mitochondria, caspase‐3 activation, and necrotic cell death
Authors: Huang Hsueh‐Meei , Ou Hsiu‐Chong , Xu Hui , Chen Huan‐Lian , Fowler Corinne , Gibson Gary E.
Published: February 2004

Mitochondrial dysfunction has been implicated in cell death in many neurodegenerative diseases. Diminished activity of the α‐ketoglutarate dehydrogenase complex (KGDHC), a key and arguably rate‐limiting enzyme of the Krebs cycle, occurs in these disorders and may underlie decreased brain metabolism. The present studies used α‐keto‐β‐methyl‐n‐valeric acid (KMV), a structural analogue of α‐ketoglutarate, to inhibit KGDHC activity to test effects of reduced KGDHC on mitochondrial function and cell death cascades in PC12 cells. KMV decreased in situ KGDHC activity by 52 ± 7% (1 hr) or 65 ± 4% (2 hr). Under the same conditions, KMV did not alter the mitochondrial membrane potential (MMP), as assessed with a method that detects changes as small as 5%. KMV also did not alter production of reactive oxygen species (ROS). However, KMV increased lactate dehydrogenase (LDH) release from cells by 100 ± 4.7%, promoted translocation of mitochondrial cytochrome c to the cytosol, and activated caspase‐3. Inhibition of the mitochondrial permeability transition pore (MPTP) by cyclosporin A (CsA) partially blocked this KMV‐induced change in cytochrome c (−40%) and LDH (−15%) release, and prevented necrotic cell death. Thus, impairment of this key mitochondrial enzyme in PC12 cells may lead to cytochrome c release and caspase‐3 activation by partial opening of the MPTP before the loss of mitochondrial membrane potentials. © 2003 Wiley‐Liss, Inc.
Repression of phospho‐JNK and infarct volume in ischemic brain of JIP1‐deficient mice
Authors: Im Joo‐Young , Lee Ko‐Woon , Kim Man Ho , Lee Si Hyoung , Ha Hye‐Yeong , Cho Ik‐Hyeun , Kim Doyeun , Yu Myung Sik , Kim Jung‐Bin , Lee Ja‐Kyeong , Kim Young Joo , Youn Byung‐Woo , Yang Sung‐Don , Shin Hee‐Sup , Han Pyung‐Lim
Published: February 2004

Mice lacking JIP1, a scaffold protein that organizes JNK pathway components, were constructed independently by two groups. The proposed in vivo function, however, remains contradictory; One study reported that targeted disruption of the jip1 caused embryonic death due to the requirement of JIP1 for fertilized eggs (Thompson et al. [2001] J. Biol. Chem. 276:27745–27748). In contrast, another group (Whitmarsh et al. [2001] Genes Dev. 15:2421–2432) demonstrated that JIP1‐deficient mice were viable and that the JIP1 null mutation inhibited the kainic acid‐induced JNK activation and neuronal death. The current study was undertaken to re‐elucidate the in vivo roles of JIP1 using newly generated JIP1 knockout mice. Our JIP1‐deficient mice were viable and healthy. The transient focal ischemic insult produced by middle cerebral artery occlusion (MCAO) strongly activated JNK in brain of jip1+/+, jip1+/−, and jip1−/− mice. Increased JNK activity was sustained for more than 22 hr in jip1+/+ and jip1+/−, whereas it was repressed rapidly in jip1−/−. Concomitantly, the infarct volume produced by the ischemic insult in jip1−/− was reduced notably compared to that in jip1+/+ brain. These results suggest that JIP1 plays a pivotal role in regulating the maintenance of phosphorylated JNK and neuronal survival in postischemic brain, but is not essential for JNK activation and early development. © 2003 Wiley‐Liss, Inc.
Brain transplantation of genetically engineered human neural stem cells globally corrects brain lesions in the mucopolysaccharidosis type VII mouse
Authors: Meng Xing‐Li , Shen Jin‐Song , Ohashi Toya , Maeda Hiroshi , Kim Seung Up , Eto Yoshikatsu
Published: February 2004

In the present study, we investigated the feasibility of using human neural stem cells (NSCs) in the treatment of diffuse central nervous system (CNS) alterations in a murine model of mucopolysaccharidosis VII (MPS VII), a lysosomal storage disease caused by a genetic defect in the β‐glucuronidase gene. An immortalized NSC line derived from human fetal telencephalon was genetically engineered to overexpress β‐glucuronidase and transplanted into the cerebral ventricles of neonatal MPS VII mouse. Transplanted human NSCs were found to integrate and migrate in the host brain and to produce large amount of β‐glucuronidase. Brain contents of the substrates of β‐glucuronidase were reduced to nearly normal levels, and widespread clearing of lysosomal storage was observed in the MPS VII mouse brain at 25 days posttransplantation. The number of engrafted cells decreased markedly after the transplantation, and it appears that the major cause of the cell death was not the immune response of the host but apoptotic cell death of grafted human NSCs. Results showed that human NSCs would serve as a useful gene transfer vehicle for the treatment of diffuse CNS lesions in human lysosomal storage diseases and are potentially applicable in the treatment of patients suffering from neurological disorders. © 2003 Wiley‐Liss, Inc.
Polymerization reaction engineering: past, present and future
Authors: Ray W. Harmon , Soares João B.P. , Hutchinson Robin A.
Published: February 2004

In this short review we describe some of the main developments of polymer reaction engineering since the early days of polymer science in the 1930's to the current challenges of today.
Temperature oscillation calorimetry by means of a Kalman‐like observer: the joint estimation of Qr and UA in a stirred tank polymerization reactor
Authors: Freire Fábio Bentes , Giudici Reinaldo
Published: February 2004

The present work is concerned with the joint estimation of the rate of heat produced by the emulsion terpolymerization of styrene, butyl acrylate and methyl methacrylate (Qr), and the overall heat transfer coefficient (UA) from temperature measurements and reactor heat balance. By making specific assumptions on the dynamics of the parameters UA and Qr, we designed a Kalman‐like observer to carry out the estimation of these two time‐varying parameters, without the need for neither additional measurements nor on‐line samples. Temperature oscillations are induced in the cooling jacket in order to ensure the observability of the system. One further aspect of our approach is that it only requires the reactor energy balance to perform the estimation.
Simulating cumulative distributions under transient conditions in well‐mixed, continuous and batch polymerization reactors
Authors: Sachs William H.
Published: February 2004

Instantaneous property methods are applied to the simulation of cumulative distributions of polymer chain architecture in well‐mixed, continuous and batch reactors. We show how cumulative distributions can be simulated under transient conditions using a general convolution integral and suitable output from a dynamic reactor simulation package such as POLYREDTM. We also show how the state equations that describe a polymerizing system can be augmented for direct simulation of these distributions. Examples of the impact of catalyst kinetics, reactor operating policies, and process upsets on the molecular weight distribution of bimodal high molecular weight polyethylene produced in well‐mixed, stirred‐bed gas‐phase reactors are simulated for a binary transition‐metal catalyst system.
Butyl acrylate/methyl methacrylate latexes: adhesive properties
Authors: Jovanović Renata , Ouzineb Keltoum , McKenna Timothy F. , Dubé Marc A.
Published: February 2004

In this study, butyl acrylate/methyl methacrylate (BA/MMA) latexes of bimodal molecular weight and particle size distribution were prepared in a multi‐step process by seeded conventional emulsion and seeded miniemulsion polymerization. For the conventional emulsion case, a BA/MMA batch copolymerization was conducted as a first step (seed generation) and was followed by a monomer addition step to ensure particle growth. In a third step, a BA/MMA pre‐emulsified mixture was added to generate a second particle population. For the miniemulsion case, a BA/MMA copolymerization was carried out as a first step (seed generation) and was followed by a monomer addition step. The addition of a BA/MMA miniemulsion served to generate a bimodal particle size and molecular weight distribution. The final latexes were coated onto a polyethylene terephthalate carrier, dried and their performance as pressure‐sensitive adhesives was evaluated using tack, peel and shear adhesion measurements. Structure‐property relationships between the adhesive properties and the weight‐average molecular weight and average particle size were examined. Even though the polymers obtained by miniemulsion showed better shear resistance, their shear resistance was low. There was no statistically significant difference in peel resistance of the polymers obtained by the two reactions. While a significant difference in tackiness between the two emulsion procedures was found when the adhesives were tested using the less sensitive, rolling ball test, no differences were found when they were tested using a loop tack test.
An experimental and numerical study on crystallization analysis fractionation (Crystaf)
Authors: Anantawaraskul Siripon , Soares João B.P. , Wood‐Adams Paula M.
Published: February 2004

Crystallization analysis fractionation (Crystaf) is a new technique used to estimate the chemical composition distribution (CCD) of semi‐crystalline copolymers. In this study, the effect of chain microstructure and operation parameters on Crystaf profiles was investigated using a series of ethylene/1‐hexene copolymers and their blends. The Crystaf profiles were also modeled via stochastic simulation based on the distribution of average ethylene sequence lengths.
Chemical composition distribution of multicomponent copolymer chains
Authors: Anantawaraskul Siripon , Soares João B.P. , Wood‐Adams Paula M.
Published: February 2004

Probability theory was used to model the microstructure of copolymer chains. Specifically, we derived analytical expressions to describe the chemical composition distribution of multicomponent random copolymers and the longest monomer sequence length distribution of binary copolymers. The results agree with Stockmayer's distribution for binary copolymers and with Monte Carlo simulations for multicomponent copolymers.
A new tool for the study of polymerization under supercritical conditions – preliminary results
Authors: Fortini Sophie , Lavanchy Frédéric , Nising Philip , Meyer Thierry
Published: February 2004

Efficient stirring is needed to realize heat flow analysis with a thermally homogeneous medium. Because dispersion polymerization with supercritical fluids can be destabilized under stirring, a preliminary target has been to find a compromise between synthesis and basic reaction calorimetry requirements. This paper describes the use of poly (dimethylsiloxane) macromonomer with a molecular weight 5000 g/mol as stabilizer for the dispersion polymerization of methyl methacrylate in supercritical carbon dioxide. The effect of stirring speed and stabilizer concentration has been examined. This study has shown that poly (methyl methacrylate) can be produced at high yield and molecular weight using 10 wt% (respect to monomer) poly (dimethylsiloxane) macromonomer at stirring speeds up to 600 rpm. A polymerization enthalpy of −57.6±2 kJ/mol has been calculated being in good agreement with previously reported data. Thus, preliminary results for the heat balance using the newly developed high pressure reaction calorimeter for supercritical fluid applications have shown the important potential of reaction calorimetry to promote supercritical fluid technologies at industrial scale allowing for the determination of kinetics and thermodynamic and safety data, respectively.
On growth patterns of branched polymer architectures
Authors: Iedema Piet D. , Hoefsloot Huub C.J.
Published: February 2004

In nature trees may have many different forms and so have all natural branched structures. Differences in branched architectures of synthetic polymers can only be explained by kinetics. We compare radical polymerization of low density Polyethylene (PE) and PE polymerization with Constrained Geometry Catalyst (CGC) metallocene. The architectures generated by our synthesis algorithms revealed marked differences between the two PE‐systems. Metallocene‐PE turned out to be more comb‐like. This could partially be explained by analyzing growth patterns of the two PE types as incorporated in the architecture synthesis algorithms.
Compartmentalisation in miniemulsions: exploration of compartmentalisation and some interesting end‐uses
Authors: Ouzineb Keltoum , Graillat Christian , Dubé Marc A. , Jovanović Renata , McKenna Timothy F.
Published: February 2004

Infrared spectroscopy and differential scanning calorimetry were used to demonstrate that miniemulsions of relatively hydrophobic monomers are compartmentalised during the reaction. Experiments with blends of miniemulsions of different composition revealed that no mass transfer takes place between droplets of different composition in the same reactor. In addition, it was shown that it is possible to make high solids content, low viscosity latexes with bimodal particle size and molecular weight distributions because of this property.
Batch process monitoring and its application to polymerization systems
Authors: Ündey Cenk , Ertunç Sinem , Tatara Eric , Teymour Fouad , Çιnar Ali
Published: February 2004

Slight changes in raw material properties or operating conditions during critical periods of operation of batch and semi‐batch polymerization reactors may have a strong influence on reaction mechanism and impact final product quality. Online process monitoring, fault detection, fault diagnosis, and product quality prediction in real‐time ensure safe reactor operation and warn operators about excursions from normal operation that may lead to deterioration in product properties. Multivariate statistical process monitoring and quality prediction using multiway principal components analysis and multiway partial least squares have been successful in detecting abnormalities in process operation and product quality. When abnormal process operation is detected, fault diagnosis tools are used to determine the source cause of the deviation. Illustrative case studies are presented via simulated polyvinyl acetate polymerization.
On‐line monitoring of all‐acrylic emulsion polymerization reactors by Raman spectroscopy
Authors: Elizalde Oihana , Leiza Jose Ramon , Asua José M.
Published: February 2004

Fourier Transform Raman spectroscopy was used as an on‐line sensor in order to monitor high solids content (50 wt%) n‐BA/MMA emulsion copolymerization reactions. Due to the similarity of the chemical structure of the monomers, no separate bands could be detected for each monomer, and therefore a multivariate calibration technique was required (Partial Least Squares Regression, PLSR). Using experimental data from several semi‐batch reactions independent PLSR models were built for the solids content, cumulative copolymer composition and unreacted amounts of n‐BA and MMA. Those models were experimentally validated by monitoring reactions not used for calibration. It is demonstrated that FT‐Raman spectroscopy can be successfully applied to on‐line monitor emulsion polymerization reactors. This technique also shows a high potential for process control purposes because independent information about several molecular properties can be obtained from a single apparatus.
Branching and crosslinking in emulsion polymerization
Authors: Bouvier‐Fontes Ludivine , Pirri Rosangela , Arzamendi Gurutze , Asua José M. , Leiza Jose R.
Published: February 2004

The seeded semibatch emulsion polymerization of butyl acrylate (BA) with allyl methacrylate (AMA) and butanediol diacrylate (BDA) was used to study the influence of the crosslinkers on the kinetics, branching and crosslinking density, gel fraction and sol MWD produced during the experiments carried out at 80°C using potassium persulfate as initiator. Surprisingly, the most reactive crosslinker, BDA, produced the less crosslinked, branched and gel containing polymer. These results were explained with the help of a mathematical model in terms of cyclization reactions and diffusion controlled propagation and termination reactions.
Comparing near infrared and Raman spectroscopy for on‐line monitoring of emulsion copolymerization reactions
Authors: Reis Marlon M. , Araújo Pedro H.H. , Sayer Claudia , Giudici Reinaldo
Published: February 2004

In this work, Raman and Near InfraRed (NIR) spectroscopies are evaluated for the monitoring of different semicontinuous emulsion homo‐ and co‐polymerization reactions. Important process variables, namely monomer concentrations and average particle sizes, were monitored by both techniques under realistic conditions that would be found in an industrial environment (e.g. low signal/noise ratio, probe placed in the reaction medium). Results suggest that Raman and NIR are suitable for on‐line monitoring of emulsion polymerization reactions and that the success of their application is mainly related to representative calibration models used for the estimation of the properties of interest.
Butyl acrylate and vinyl acetate semicontinuous emulsion copolymerizations: study of stabilization performance
Authors: Araújo Pedro H. H. , Giudici Reinaldo , Sayer Claudia
Published: February 2004

The use of small amounts of carboxylic monomers in industrial recipes with high solids content enhances colloidal stability due to the presence of carboxylic groups on the outer surface of the polymer particles. Understanding the relationship between several different but interdependent phenomena, including particle nucleation, kinetics, particle aggregation, monomer type, solids content, the role of the carboxylic monomer and the influence of reaction temperature may improve the control over particle size and latex stability. In this work, the kinetics and stabilization performance of semicontinuous vinyl acetate (VA) and butyl acrylate (BA) emulsion copolymerization reactions are studied under different reaction temperatures, acrylic acid (AA) concentrations, solids contents and monomer feed compositions. Results show that choosing optimal AA concentrations and reaction temperatures are key factors in order to enhance the stabilization performance in semicontinuous VA/BA emulsion copolymerization.
Analysis of mass transport limitation during emulsion polymerization using reaction calorimetry and conductivity measurement
Authors: Henninger Björn , Rehfeld Matthias , Pauer Werner , Moritz Hans‐Ulrich
Published: February 2004

The seeded emulsion polymerization of styrene was investigated by reaction calorimetry in combination with conductivity measurements using the RC1e calorimeter (Mettler Toledo). Varying the stirrer speed showed the existence of mass transport limitation in the lower speed range. For the case of using the autoclave HP60 with an anchor stirrer a minimum stirrer speed of 400 rpm is required to be sure of adequate mixing in the reactor.
Analysis of particle formation under monomer‐starved conditions in emulsion polymerization reactors
Authors: Sajjadi Shahriar , Yianneskis Michael
Published: February 2004

An important characteristic of monomer‐starved nucleation in semibatch reactors is that the rate of growth of particles is controlled by the rate of monomer addition. The reduced rate of growth of particles prolongs the nucleation interval by slowing down the rate of emulsifier micelle depletion and forms a larger number of particles (Np). Model calculations show how Np varies with the formulation parameters as the monomer‐flooded nucleation shifts into monomer‐starved one. Particle formation in the intermediate conversion of interval III of the styrene batch emulsion polymerization also showed an enhancement because of a low rate of growth of newly formed particles. However, at a higher conversion, the rate of particle formation decreased significantly. Modeling results show that the reduction in the rate of particle formation at high conversions could not be simply explained by existing theories which rely on the decrease in monomer concentration in the aqueous phase as a means to explain the decrease in the rate of radical capture.
Diffusion‐controlled reactions in vinyl chloride suspension polymerization
Authors: De Roo Tony , Heynderickx Geraldine J. , Marin Guy B.
Published: February 2004

The vinyl chloride suspension polymerization is kinetically modeled with a general approach for the independent calculation of diffusion effects on polymerization reactions. For the initiator decomposition, propagation and termination an apparent rate coefficient is determined, built up from two contributions: the intrinsic rate coefficient and a diffusional contribution. The diffusional contribution is calculated with the Smoluchowski model, the diffusion coefficients being determined from the free volume theory. When applying the free volume theory no adjustable parameters are used. The intrinsic rate coefficients are taken from the literature. Hence, a model without any adjustable parameters is obtained. Calculations show that the glass effect appears only at (very) high conversions. Due to the cage effect the initiator efficiency decreases strongly as soon as the monomer phase has disappeared. The gel effect always occurs in the polymer‐rich phase and results in a decrease of the termination rate coefficient at the start of the third stage in the polymerization process. There is a good agreement with experimental results.
Continuous styrene – methyl methacrylate – glycidyl methacrylate terpolymerizations in homogeneous mixtures with supercritical carbon dioxide
Authors: Beuermann Sabine , Buback Michael , Gadermann Moritz , Jürgens Michael , Günzler Fabian
Published: February 2004

Free‐radical terpolymerizations of styrene, methyl methacrylate, and glycidyl methacrylate were carried out in a tubular reactor in the presence of 20 wt.% CO2 at temperatures between 120 and 180°C and pressures of 300 and 350 bar. The number average molecular weights, MN, were mostly between 2000 and 3000 g·mol−1 and polydispersity indices around 2. In part of the experiments molecular weights were controlled by n‐dodecyl mercaptan serving as the chain‐transfer agent. PREDICI modeling indicates that the targeted molecular weights of MN∼2500 g·mol−1 and polydispersities around 2 may also be reached by using an initiator cocktail, a mixture of two initiators with significantly different decomposition rate coefficients. The predictions are confirmed experimentally.
Simulation model for urea‐formaldehyde reactors
Authors: Mejdell Thor , Schjønsby Hans K.
Published: February 2004

A comprehensive simulation model for urea/formaldehyde (UF)‐resins has been developed. The model utilizes kinetic results reported in the literature for low molecular weight systems and extends these to higher molecular weight systems by using a functional group approach. The model consists of

‐ 9 functional groups, 5 urea groups and 4 formaldehyde groups.

‐ 9 reactions, 5 methylolation reactions and 4 condensation reactions. In all these reactions both the formation and the decomposition reactions are included.

All the kinetic constants are pH and temperature dependent.

Two batch runs with different U/F ratios were used to adjust a couple of model parameters. Samples from these batch runs were analyzed with HPLC for low molecular weight compounds, and GPC for the average molecular weight. A run with continuous IR measurement showed excellent fit for the formaldehyde concentration. The model also estimates the viscosity from the functional groups.
On the evolution of particle size average and size distribution in suspension polymerization processes
Authors: Jahanzad Fatemeh , Sajjadi Shahriar , Brooks Brian W.
Published: February 2004

The dispersion of methyl methacrylate (MMA) and its suspension polymerization were used as models to elaborate the evolution of particle size average and size distribution in the course of suspension polymerization. The underlying mechanisms for the occurrence of the dynamic and static steady states in the population of drops were defined and their effects on the evolution of drop/particle size average and size distributions were examined. The characteristic intervals of suspension polymerizations (transition, steady‐state, growth, and identification) were elaborated. The formation of satellite droplets and their evolution in the course of polymerization were also discussed.
Achieving high conversions in nitroxide‐mediated living styrene miniemulsion polymerization
Authors: Lin Marcus , Cunningham Michael F. , Keoshkerian Barkev
Published: February 2004

Nitroxide‐mediated living radical polymerizations of styrene were run in miniemulsion. Using a modified miniemulsion process that does not require the use of a volatile costabilizer, near complete conversions could be achieved in 2‐3 hours while preserving narrow molecular weight distributions and a high degree of chain livingness. Increased rates and final conversions were achieved by semi‐batch addition of the nitroxide scavenger ascorbic acid.
Determination of polybutylene terephthalate polycondensation equilibrium constant using a batch reactor
Authors: Darda Pranay Jairam , Hogendoorn Kees , Molenkamp Tjaart , Versteeg Geert
Published: February 2004

The PBT polycondensation equilibrium constant at 255°C was determined using a batch reactor. Starting from a Polybutylene terephthalate (PBT) prepolymer having a degree of polymerisation of 12.7, equilibrium experiments were performed in the range of 1 to 50 mbar. The equilibrium degree of polymerisation (i) was determined indirectly using dilute solution viscometry of a solution of 1 weight % PBT in m ‐ cresol. The degree of polymerisation of PBT obtained at equilibrium in the range of 1 to 50 mbar at 255°C as a function of the BDO partial pressure (mbar) could be expressed by: i = 111.47 − 86.18 exp(−1.14 $P^{-1.44}_{bdo}$
). The equilibrium solubility of 1,4 butanediol (BDO) in the PBT melt was derived form the BDO partial pressure using the Flory ‐ Huggins theory. The PBT polycondensation reaction equilibrium constant was related to the degree of polymerisation by the equation: $K_e = {0.187 \over 1 -19243 e^{-0.3932}} $ in the range i = 26 − 100. The PBT polycondensation equilibrium constant at high degrees of polymerisation is in line with literature data and thermodynamics.
Multi‐objective dynamic optimization of semi‐batch polymerization processes
Authors: Martins da Silva Cláudia , Chalbaud Biscaia Evaristo
Published: February 2004

An improved evolutionary algorithm is proposed to perform multi‐objective dynamic optimization of a semi‐batch styrene polymerization process. The target is to determine the optimal feeding trajectories and the reactor operating temperature, which maximize the monomer conversion rate and minimize the initiator residue concentration in the final product. The optimization problem has been formulated as a multi‐objective mixed‐integer nonlinear problem (MOMINLP). The proposed approach allows the effective computation of the optimal operating strategies for the production of polymers with the average molecular weight and the polydispersity index required.
Kinetic modeling of aggregation and gel formation in quiescent dispersions of polymer colloids
Authors: Lattuada Marco , Sandkühler Peter , Wu Hua , Sefcik Jan , Morbidelli Massimo
Published: February 2004

In this work, a methodology suitable for the description of aggregation and gel formation processes of polymeric colloidal dispersions in quiescent conditions is presented. The modeling of aggregation is based on the use of populations balance equations to describe the time evolution of the aggregate distribution. Monte‐Carlo simulations are used to generate the structural properties of individual aggregates, which are necessary to compute the average radius of gyration and hydrodynamic radius that are compared to the values measured using light scattering. The agreement between model predictions and measured sizes is good in both diffusion‐limited and reaction‐limited conditions. For the description of progress toward gel formation, the cumulatively occupied volume, a measure of the fraction of space occupied by the clusters, is defined. Due to the fractal nature of clusters, during the aggregation the system can reach a condition of space filling, after which the formation of gel is a result of the interconnection of the clusters. It is found that in diffusion‐limited conditions the interconnection step is much faster than the preceding aggregation, while in reaction‐limited conditions the aggregation and the interconnection are of comparable duration.
Ultrasound‐induced polymerization of methyl methacrylate in liquid carbon dioxide: a clean and safe route to produce polymers with controlled molecular weight
Authors: Kemmere Maartje , Kuijpers Martijn , Jacobs Leon , Keurentjes Jos
Published: February 2004

Ultrasound‐induced cavitation is known to enhance chemical reactions as well as mass transfer at ambient pressures. Ultrasound is rarely studied at higher pressures, since a high static pressure hampers the growth of cavities. Recently, we have shown that pressurized carbon dioxide can be used as a medium for ultrasound‐induced reactions, because the static pressure is counteracted by the higher vapor pressure, which enables cavitation. With the use of a dynamic bubble model, the possibility of cavitation and the resulting hot‐spot formation upon bubble collapse have been predicted. These simulations show that the implosions of cavities in high‐pressure fluids generate temperatures at which radicals can be formed. To validate this, radical formation and polymerization experiments have been performed in CO2‐expanded methyl methacrylate. The radical formation rate is approximately 1.5*1014 s−1 in this system. Moreover, cavitation‐induced polymerizations result in high‐molecular weight polymers. This work emphasizes the application potential of sonochemistry for polymerization processes, as cavitation in CO2‐expanded monomers has shown to be a clean and safe route to produce polymers with a controlled molecular weight.
Thermodynamics of polymer systems
Authors: Sadowski Gabriele
Published: February 2004

This work gives an introduction into the thermodynamic modeling of polymer systems. After a short overview about the different basics of thermodynamic models, results obtained with the recently proposed PC‐SAFT equation of state are discussed exemplarily for systems containing polymers as well as copolymers.
Microemulsion polymerization for producing fluorinated structured materials
Authors: Apostolo Marco , Biressi Giovanni
Published: February 2004

When perfluoropolyether microemulsions are used during polymerization of fluoropolymers, the structure of the reaction environment can be strictly controlled. In particular, the number and size of polymer particles in latexes can be set freely, yielding a number of advantages.

First, as a result of radical segregation, terminations can be decreased without reducing polymerization rate: in this way high molecular weights are easily obtained also with poorly reactive monomers.

Moreover, in combination with a reversible chain transfer mechanism based on iodine, particle segregation allows establishing pseudo‐living polymerization conditions. In this situation formation of long branches in the polymer can be controlled by using bifunctional molecules that are able to link two different polymer chains to each other during polymerization. This is the so‐called “branching and pseudo‐living” technology.

Finally, by co‐coagulating latexes of different polymers prepared by microemulsion polymerization, very small particles and, thus, high interface areas are generated. In this way properties of different polymers, such as fluoroelastomers and fluorinated semicrystalline polymers, are matched effectively, generating new nanocomposite materials that exhibit outstanding properties.

In this paper these results are reported and an overview of some novel sophisticated fluoropolymers obtained in microemulsion is given.
Rate mechanisms of a novel thiol‐ene photopolymerization reaction
Authors: Reddy Sirish K. , Cramer Neil B. , O' Brien Allison K. , Cross Tsali , Raj Rishi , Bowman Christopher N.
Published: February 2004

A novel thiol‐ene photopolymerization reaction involving copolymerization of tetrathiol monomer with vinyl silazane is experimentally characterized and is modeled successfully. The overall polymerization rate is found to be controlled by the ratio of the propagation to chain transfer kinetic parameters. The polymerization rate of this mixture, in the presence of added photoinitiator, is approximately first order in ene functionality and is independent of thiol functional group concentration. Initiation rates in this system, when cured utilizing a light centered around 365 nm light, and in the presence of no added photoinitiator, are shown to be proportional to the ene monomer concentration. When the mixture is polymerized utilizing light centered at 254 nm light, and without photoinitiator, the initiation rates are proportional to the thiol monomer concentrations. This novel reaction scheme is further utilized to form ultra rapidly polymerizable polymer derived ceramic structures with high aspect ratios.
Syndiospecific polymerization of styrene with embedded metallocene catalysts
Authors: Chung Jin Suk , Woo Boo Gon , Choi Kyu Yong
Published: February 2004

Syndiotactic polystyrene (sPS) is a highly crystalline polymer with high melting point (270°C). The syndiospecific polymerization of styrene to sPS with metallocene catalysts is characterized by significant phase changes that lead to global gelation. Since sPS does not dissolve in styrene or solvents such as toluene and n‐heptane, sPS precipitates out immediately from the liquid phase with the start of polymerization. The polymer crystallites aggregate to primary particles and they develop to a gel. The gelation is not due to cross‐linking polymerization but due to strong molecular interactions between the polymer and monomer molecules. In this work, homogeneous Cp*Ti(OMe)3 catalyst is heterogenized or embedded into sPS prepolymer particles. The embedded catalyst has been tested in a laboratory scale diluent slurry process to illustrate the feasibility of slurry phase polymerization for the synthesis of sPS particles.
New routes to high solid content latexes: a process for in situ particle nucleation and growth
Authors: Boutti Salima , Graillat Christian , McKenna Timothy F.
Published: February 2004

A means of generating latices with solid contents well over 70% (v/v) without the use of intermediate seeds is proposed. It is demonstrated that the use of an electrically neutral initiation system (hydrogen peroxide) in the initial stages of the process, followed by an initiator yielding negatively charged free radicals (ammonium persulphate) changes the way in which the system generates stable particles. The reason for this change is the need to avoid stabilising small, homogeneously nucleated particles during the first portion of the process, and the desire to generate controlled quantities of them during the second portion. The processes are highly reproducible, as are the particle size distributions and rheological properties of the final latices.
Simulating acrylate polymerization reactions: toward improved mechanistic understanding and reliable parameter estimates
Authors: Busch Markus , Müller Matthias
Published: February 2004

It is well accepted that free‐radical acrylate polymerizations are governed by a complex coupled kinetic mechanism consisting of propagation, termination and inter‐molecular transfer to small species such as monomer or modifiers, together with intra‐ and inter‐molecular transfer reactions to polymer. Propagation, β‐scission or termination of the transient secondary/tertiary radicals formed following transfer to polymer is possible. This reaction cascade strongly affects the micro‐structural characteristics of the polymer and its application properties. Individual parts of this mechanism have been discussed on many occasions. However, a general approach for determining the rate coefficients for the full kinetic scheme has been missing. Such an approach is developed in this communication.
Simulation of gel permeation chromatography measurement for long chain branched metallocene polyethylene
Authors: Liu Nannan , Wood‐Adams Paula
Published: February 2004

The research about the polymerization reaction mechanism of long chain branched polymer provides a method to simulate the generation of LCB mPE (long chain branched metallocene polyethylene).[1‐3] In this work, after simulating the generation of one million LCB mPE molecules, we calculate the sizes (i.e. radii of gyration) of molecules in good solvents to obtain the molecular size distributions. Then we simulate the fractionation in GPC (gel permeation chromatography) measurement and the different GPC detector responses to obtain simulated GPC MWDs (molecular weight distributions). The simulated MWDs are compared to the real GPC results provided by the Dow Chemical Company.