Les normes concernant les émissions de formaldéhyde des adhésifs pour bois étant très restrictives, des alternatives satisfaisant les mêmes exigences sont recherchées. Dans cette perspective nous avons étudié des solutions pour l'utilisation industrielle de trois types d'adhésifs que sont les tanins réagissant par autocondensation, les résines hybrides d'uréeformaldéhyde (UF)/polyméthylènediisocyanate (pMDI) et les formulations à base de diméthoxyéthanal (DME). L’étude portant sur les tanins a montré qu’une production industrielle de panneaux à grosses particules pressés à injection de vapeur est possible. Les études ont permis d’évaluer le durcissement du mélange adhésif et de l’optimiser pour le pressage à injection de vapeur. La plupart des formulations étudiées satisfont les exigences qualitatives des normes1. Cependant la résistance à l’eau de ces panneaux reste problématique. L’expérimentation menée sur les adhésifs UF/pMDI apporte une meilleure connaissance de ceux-ci et de leurs interactions avec les propriétés finales des panneaux de fibres. Des résultats intéressants ont été obtenus lors de l’étude de la distribution de la résine par microscopie confocale à balayage laser (MCBL). L’amélioration des caractéristiques des panneaux permet de satisfaire aux exigences de la norme F** pour des adhésifs UF/pMDI émulsifiable ayant un faible rapport molaire. Toutefois les dégagements F**** n’ont pu être atteints seulement qu’en utilisant 100 % de MDI. Dans l’étude portant sur des formulations dérivées de DME, de nouvelles formulations d’adhésifs ont été développées et certaines ont été validées à l’échelle industrielle. Celles-ci satisfont les exigences qualitatives des normes, et ont des émissions de formaldéhyde correspondantes aux panneaux de la classe F****. / The standards concerning the formaldehyde emissions2 from wood based panels have become more restrictive; alternatives meeting the requirements of the standards are needed. Therefore, solutions for the industrial use of three types of adhesives were studied which are; tannin adhesives by silica-induced autocondensation, Urea-formaldehyde (UF) / polymeric phenyl isocyanate (pMDI) hybrid adhesives and formulations based on dimethoxyethanal (DME). The study related to the tannins showed that an industrial production of large particle particle boards pressed with steam injection is possible. The analyses made it possible to evaluate the tannin autocondensation reactions of the formulations and to optimize them for steam injection pressing. Most of the studied formulations satisfied the qualitative requirements of the standard for both internal bond strength and formaldehyde emission2. Besides, the potential use for exterior grade of these panels remains problematic. The experimentations on the UF/pMDI adhesives increased the knowledge in the field of the adhesives-panel properties interactions for medium density fiberboard (MDF). Important results were obtained by the study of the resin distribution by confocal laser scanning microscopy (CLSM). Best results concerning the improvement of the panel properties were obtained for adhesive mixtures with low molar ratio UF and emulsifiable pMDI, satisfying the requirements of the standard, grade F **. However, grade F **** could only be reached by using 100 % of MDI. During the study related to the formulations of DME derived resins, new adhesive formulations were developed. The most promising formulation was selected and validated on industrial scale. It has shown to be able to satisfy the qualitative requirements of the standards with low formaldehyde emission2.

Thesis--PlanB (M.S.)--University of Wisconsin--Stout, 2001. / Includes bibliographical references.

Diss. (sammanfattning) Stockholm : Univ., 2004. / Härtill 6 uppsatser.

Thesis (Ph. D.)--University of Chicago, Dept. of Chemistry, March 2001. / Includes bibliographical references. Also available on the Internet.

Thesis (doctoral)--Lund University, 1994.

Thesis (doctoral)--Lund University, 1994.

Isocyanates are invaluable bulk chemicals that play a central role in the synthesis of various polymers and provide a key platform for the synthesis of nitrogen-containing molecules such as carbamates and ureas. Unfortunately, isocyanates suffer from high toxicity, low functional group tolerance, and a propensity to undergo deleterious side-reactions. Consequently, blocked (masked) isocyanate derivatives have been the subject of increased interest resulting from their reduced toxicity and exceptional control over isocyanate reactivity. This strategy has largely been relegated to the polymerization literature, although its use in the synthesis of complex urea and carbamate derivatives is well established in synthetic organic chemistry. However, prominent gaps in the blocked isocyanate literature were clear at the outset of this research project. First and foremost, the development of heteroatom-substituted isocyanates, such as N- and O-substituted derivatives, remained relatively scarce despite their potential for the synthesis of important nitrogen-containing derivatives. Furthermore, the additions of carbon-centred nucleophiles on blocked N-, O-, and even C-substituted blocked isocyanates were exceedingly rare. Finally, the use of a blocking group strategy in catalytic transformations of isocyanates remained largely absent from the literature. This was particularly striking given the widespread development of catalytic transformations of isocyanates. As such research efforts began focusing on furthering the development of blocked N-isocyanates as a vital platform for heterocyclic synthesis (chapter 2). Initially, the cascade reactivity of blocked N-iso(thio)cyanates was expanded to incorporate electrophiles such as alkynes (section 2.2). This readily provided access to imidazolone and thiazolidine products. Subsequently, the development of a cascade reaction providing access to 1,2,4-triazin-3(2H)-ones was explored (section 2.3). This provided the first examples of an N-isocyanate cascade which hinged on the use of acid catalysis. Moreover, insight into hydrazone isomerization was gained. Finally, these efforts culminated in the development of cascade reactions providing access to a rare class of 1,2,4-triazinones as well as 5-aminopyridazinones (section 2.4). This provided the first example of a cascade reaction involving a C-C bond formation onto a blocked N-isocyanate derivatives. Furthermore, this development was pivotal in re-focusing attention on the development of general strategies to achieve addition of carbon nucleophiles onto blocked isocyanate derivatives. Towards this end, the development of two strategies to achieve carbon-centred nucleophilic additions on both blocked N- And O-isocyanates were developed (chapter 3). Inspiration from the isocyanate literature led to the development of carboxylic acids as formal carbon nucleophiles (section 3.2). This strategy was found to be quite general for the synthesis of hydroxamates from blocked O-isocyanates. Furthermore, encouraging results were generated on the ability of Grignard reagents to form similar products (section 3.3). Particularly important is the paradigm shift this allows from C-N bond formation to C-C bond formation for the synthesis of hydroxamate derivatives. Furthermore, lead results suggest the potential of this reactivity to translate to blocked N-substituted derivatives, a transformation which had failed with carboxylic acids. Finally, the development of a catalytic amide synthesis from blocked isocyanate precursors was targeted (chapter 4). The use of a blocking group strategy was able to address the current major limitation of isocyanates as amide precursors, that is functional group tolerance (section 4.2). Indeed, a commercially available rhodium catalyst was found to allow efficient amidation of various ambiphilic blocked isocyanate derivatives using arylboroxines as nucleophiles. Mechanistic studies including the use of variable time normalization analysis supported the presence of two alternative kinetic regimes contingent on the reaction conditions employed. Furthermore, these data suggested the success of this transformation, in the case of ambiphilic derivatives, hinged on a rate determining isocyanate release (chapter 4). Finally, initial results strongly support the potential for Boc-carbamates to provide a general platform for amidation in the presence of strong nucleophiles such as primary amines. The potential of a blocking group strategy in catalytic reaction development was further displayed with the development of a palladium catalyzed amidation of blocked derivatives with arylboroxine nucleophiles (section 4.3). Indeed, the use of blocked isocyanates was found to be absolutely key in achieving efficient reactivity with the palladium catalyst. This result, coupled with the sparse reports on blocked isocyanates in catalysis, strongly suggest that the use of such a strategy could allow the development of reactivity otherwise unattainable when using free isocyanates.

Isocyanate chemistry is well-known and has been studied and exploited for years. N-Isocyanate derivatives, however, are scarce and far less understood. These are divided in three subclasses: the aminoisocyanates, the iminoisocyanates, and the rarest of them all, the amido-isocyanates. The latter are underdeveloped and understudied. Herein, studies that resulted in evidence for the existence of N_β-amido–isocyanates, and validated their use in a masked isocyanate strategy, will be described. Suitable precursors, N_β-acyl phenylcarbazide derivatives (activated aza-dipeptides), were synthesized in the context of aza-tripeptide synthesis. The 1,3,4-oxadiazol-2(3H)-one intermediate was formed quickly in the course of the reaction, and an equilibrium between the free N_β-amido-isocyanate and the 1,3,4-oxadiazol-2(3H)-ones was established. Longer reaction times, in presence of amino amide nucleophiles, led to the formation of hydantoins or aza-tripeptides with full consumption of both the starting material and the oxadiazolone intermediate, yielded 14 hydantoins and 4 aza-tripeptides in 51-79% isolated yields. Experiments were performed to support the formation of an amido-isocyanate intermediate and discriminate between pathways possibly involving the formation of a tetrahedral oxyanionic intermediate versus the trapping of an N-isocyanate by a nucleophile. A control reaction in which the N_α in the starting material was methylated completely suppressed the formation of the isocyanate intermediate and shut down the reaction, lending supporting the isocyanate formation pathway. The hydrogen at this position is crucial for the formation of the isocyanate, which can be deprotonated and form a neutral isocyanate species. To further support the mechanistic hypothesis, established C-isocyanate chemistry, in which isocyanates react with carboxylates to form amides, was applied to a series of oxadiazolones. This transformation cannot occur in the absence of an isocyanate. This reaction yielded 8 different N_β-acyl hydrazides with moderate to good yields, again supporting the formation of the rare amido-isocyanates. Overall, this work supports the formation of amido-isocyanates in equilibrium with their corresponding 1,3,4-oxadiazol-2(3H)-ones and validated that the latter are masked amido-isocyanates, species that have been rarely studied in the literature.

Thesis (M.P.H.)--University of Adelaide, Dept. of Community Medicine, 1992. / Includes bibliographical references (leaves 73-80).

Thèse de doctorat : Chimie et sciences des matériaux : Paris 12 : 2007. / Thèse uniquement consultable au sein de l'Université Paris 12 (Intranet). Titre provenant de l'écran-titre. Bibliogr. : 116 réf.