Branching theories and thermodynamics used to help designing precursor architectures and binder systems / K. Dusek in SURFACE COATINGS INTERNATIONAL. PART B : COATINGS TRANSACTIONS, Vol. 89, B2 (06/2006)  

[article]  inSURFACE COATINGS INTERNATIONAL. PART B : COATINGS TRANSACTIONS > Vol. 89, B2 (06/2006) . - p. 123-131 Titre : Branching theories and thermodynamics used to help designing precursor architectures and binder systems Type de document : texte imprimé Auteurs : K. Dusek, Auteur ; R. Barsotti, Auteur ; J. Huybrechts, Auteur ; L. A. Lewin, Auteur ; M. Duskova-Smrckova, Auteur Année de publication : 2006 Article en page(s) : p. 123-131 Note générale : Bibliogr. Langues : Anglais (eng) Catégories : Cyclisation (chimie) Gélification Liants Réseaux polymères Réticulation (polymérisation) Revêtements organiques Thermochimie Index. décimale : 667.9 Revêtements et enduits Résumé : Cross-linking hydroxy-functional stars and copolymer precursors with a triisocyanate and associated structural changes were studied theoretically and experimentally. The model of network formation was based on the statistical generation of structures from units which were in different reaction states. The differences in gel point conversion and cross-link density were interpreted in terms of precursor functionality and functionality distribution, and differences in the reactivity of functional groups. Hydroxy-functional copolymer systems containing precursors of the same number-average functionality gel at lower conversions than stars which are monodispersed mainly due to functionality distribution. The structure of copolymers characteristic of several internal cross-links contributes more to the concentration of elastically-active network chains than stars with a single cross-link. Cyclization accompanies intermolecular cross-linking; its intensity is higher for copolymer systems compared with stars. Note de contenu : - Experimental systems and methods : Precursors - Methods - Results and discussion - Network build-up from precursors differing in architecture - theoretical description - Structure evolution for cross-linking of precursors of various architectures - Thermodynamic factors DOI : 10.1007/BF02699642 En ligne : https://link.springer.com/content/pdf/10.1007/BF02699642.pdf Format de la ressource électronique : Pdf Permalink : https://e-campus.itech.fr/pmb/opac_css/index.php?lvl=notice_display&id=5383 [article]

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Scratch- and mar-resistant refinish two-pack clear coats - linear versus branched acrylics / J. Huybrechts in SURFACE COATINGS INTERNATIONAL. PART B : COATINGS TRANSACTIONS, Vol. 89, B4 (12/2006)  

[article]  inSURFACE COATINGS INTERNATIONAL. PART B : COATINGS TRANSACTIONS > Vol. 89, B4 (12/2006) . - p. 275-283 Titre : Scratch- and mar-resistant refinish two-pack clear coats - linear versus branched acrylics Type de document : texte imprimé Auteurs : J. Huybrechts, Auteur ; A. Vaes, Auteur ; K. Dusek, Auteur ; M. Duskova-Smrckova, Auteur ; R. Barsotti, Auteur Année de publication : 2006 Article en page(s) : p. 275-283 Note générale : Bibliogr. Langues : Anglais (eng) Catégories : Automobiles -- Vernis Copolymères Copolymères greffés Polyacryliques Polymères ramifiés Polyols Résistance à l'abrasion Résistance à l'usure Vernis bi-composant Index. décimale : 667.9 Revêtements et enduits Résumé : The new generation clear coats introduced in the automotive industry have improved scratch and mar resistance. It is believed that those properties are related to the introduction of new binder technologies leading to higher film cross-link densities. This was relatively easy to accomplish in the automotive industry because baking temperatures are well above the glass-transition temperature (Tg) of the final clear coat film. In car repair coatings, the cross-linking takes place under conditions where the intermediate and/or final film Tg values are above the curing temperature. Such formulations result in vitrification during the drying process, a transition during which chemical cure and solvent release are slowed down substantially. The chemical cure can be improved through more reactive and/or higher functional binders, but this shifts the gel point to shorter times in the drying cycle which may lead to more solvent entrapment, resulting in low film hardnesses and paint defects. This paper describes the overall properties of 2K-refinish clear coats based on linear versus branched, random and graft acrylic polyols. The authors will try to correlate overall properties with theoretical predictions and practical results. Note de contenu : - EXPERIMENTAL : Binders, cross-linkers and clear coat formulations - Physical measurements on clear coats - THEORETICAL BACKGROUND - Table 1 : Physical properties of linear and branched graft acrylics - Table 2 : Film Tg values, swell ratios and gel fractions at different catalyst levels and baking cycles, measurement after 30 days of ageing at room temperature - Table 3 : Gel time for a 55% solution of different acrylics activated with HDI trimer at 500 ppm DBTDL - Table 4 : Theoretical calculations of ve, WSov Wge~ and NCO conversion at the gel point for reaction of the BACR H and LACR H at different OH/NCO ratios and practical measurements Tg, Mn and Mw for film cross-linked at 140~ (I = insoluble) - Table 5 : Property balance of different clear coats based on structured acrylics versus a commercial standard applied over a dark blue metallic basecoat at specified baking conditions DOI : 10.1007/BF02765579 En ligne : https://link.springer.com/content/pdf/10.1007/BF02765579.pdf Format de la ressource électronique : Pdf Permalink : https://e-campus.itech.fr/pmb/opac_css/index.php?lvl=notice_display&id=5268 [article]

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Star oligomers and hyperbranched polymers in low VOC polyurethane coatings : Part III / J. Huybrechts in SURFACE COATINGS INTERNATIONAL, Vol. 81, N° 5 (05/1998)

[article]  inSURFACE COATINGS INTERNATIONAL > Vol. 81, N° 5 (05/1998) . - p. 234-239 Titre : Star oligomers and hyperbranched polymers in low VOC polyurethane coatings : Part III Type de document : texte imprimé Auteurs : J. Huybrechts, Auteur ; K. Dusek, Auteur Année de publication : 1998 Article en page(s) : p. 234-239 Note générale : Bibliogr. Langues : Anglais (eng) Catégories : Formulation (Génie chimique) Liants Oligomères Polymères ramifiés Polyuréthanes Revêtements bi-composant Index. décimale : 667.9 Revêtements et enduits Résumé : Hydroxyl funtional star and dendritic oligomers with a precise control of molecular weight, functionality and structure can be prepared by ring-opening polycondensation. Such polyols can be used in 2-component polyurethane (or repair points with a VOC (Volatile Organic Compound) less than 3.5 (pounds per gallons). Using the theory of branching processes, the extent of reaction at gel, gel times and molecular weight buildup during reaction with a trifunctional polyisocyanate can be calculated as a function of the functionality of the oligomer. This paper discusses those theoretical predictions and compares the results with the crosslinking behaviour of star and dendritic oligomers and blends in a 3.5 VOC compliant refinishing clear coat. Permalink : https://e-campus.itech.fr/pmb/opac_css/index.php?lvl=notice_display&id=16637 [article]

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Star oligomers for low VOC polyurethane coatings / J. Huybrechts in SURFACE COATINGS INTERNATIONAL, Vol. 81, N° 3 (03/1998)

[article]  inSURFACE COATINGS INTERNATIONAL > Vol. 81, N° 3 (03/1998) . - p. 117-127 Titre : Star oligomers for low VOC polyurethane coatings Type de document : texte imprimé Auteurs : J. Huybrechts, Auteur ; K. Dusek, Auteur Année de publication : 1998 Article en page(s) : p. 117-127 Note générale : Bibliogr. Langues : Anglais (eng) Index. décimale : 667.9 Revêtements et enduits Résumé : Hydroxyl functional star oligomers prepared by ring-opening polycondensation have a narrow molecular weight and composition distribution. Such oligomers give a solids/viscosity advantage over linear structures at the same molecular weight and can be used in low VOC two component polyurethane coatings. The solids/viscosity advantage is a combination of the highly branched structure and the narrow molecular weight distribution. Acrylic polyols formulated at the same molecular weight/polarity/average functionality and hydroxyl value give poorer drying properties. This difference can be explained by the fact that the free radical polymerisation technique leads to polymer compositions having a broad molecular weight and functionality distribution and high fractions of polymer with a low functionality. The potlife of acrylic polyols based formulations is adversely affected by the higher fractions of high molecular weight material and with a high average functionality. In low VOC polyurethane formulations star oligomers need to be formulated within a narrow range of compositions (TG, polarity), functionality and molecular weight to get an optimum balance of drying properties and potlife. Note de contenu : - HYDROXYL FUNCTIONAL (METH)ACRYLATE COPOLYMERS - FREE RADICAL POLYMERISATION - HYDROXYL FUNCTIONAL (METH)ACRYLATE COPOLYMERS - GROUP-TRANSFER POLYMERISATION - FILM FORMATION AND CROSSLINKING IN TWO COMPONENT POLYURETHANE COATINGS - STAR AND HYPERBRANCHED POLYMERS - RESULTS AND DISCUSSION : Synthesis - Solids-viscosity relation of linear against star structures - Drying-potlife of a linear acrylic against a star oligomer - Effect of star oligomer structure on drying properties Permalink : https://e-campus.itech.fr/pmb/opac_css/index.php?lvl=notice_display&id=16475 [article]

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Star oligomers with different reactivity in low VOC polyurethane coatings : part II / J. Huybrechts in SURFACE COATINGS INTERNATIONAL, Vol. 81, N° 4 (04/1998)

[article]  inSURFACE COATINGS INTERNATIONAL > Vol. 81, N° 4 (04/1998) . - p. 172-177 Titre : Star oligomers with different reactivity in low VOC polyurethane coatings : part II Type de document : texte imprimé Auteurs : J. Huybrechts, Auteur ; K. Dusek, Auteur Année de publication : 1998 Article en page(s) : p. 172-177 Note générale : Bibliogr. Langues : Anglais (eng) Tags : 'Peinture  deux  constituants'  Liant  Polyuréthane  Oligomère  'Polymère  étoile'  'Composé  organique  volatil'  réticulé'  Réticulation Index. décimale : 667.9 Revêtements et enduits Résumé : In this paper the effects of the reactivity of hydroxyl functional oligomers with a polyisocyanate crosslinking agent have been demonstrated by comparing the potlife/hardness of a 3.5 VOC two-component polyurethane clear coat based on a low TG, high reactive against a high TG, low reactive oligomer. The reaction rate of two polymers forming a crosslinked network becomes diffusion controlled when, during the reaction, the increasing TG comes close to the reaction temperature.4 If this reaction takes place in the presence of a solvent which evaporates during film formation and crosslinking, the speed of evaporation will affect both the reaction rate and the film TG. The results of this study have shown that the reactivity determines the potlife whilst the TG controls the hardness. The reactivity of blends of such oligomers against pure oligomers is different as can be calculated using the theory of branching processes and as shown from practical measurements. Blends of oligomers or a pure oligomer with up to 75% of the properties of the high TG, low reactive oligomer do show a hardness close to the properties of the low TG, high reactive oligomer which further proves that the chemical reactivity controls the overall drying performance. A fast chemical reactivity shortens the potlife with a risk of solvent entrapment near to and at the gel point which results in low hardness. Note de contenu : - THEORETICAL BACKGROUND : Star with groups of different reactivity - Network build-up and gelation - Kinetics - Mixture of more and less reactive stard - Gelation and network formation - Kinetics Permalink : https://e-campus.itech.fr/pmb/opac_css/index.php?lvl=notice_display&id=16528 [article]

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