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Enzymes are potentially useful catalysts for polymerization as well as modification of polymers. While lipases have been used previously for polymerization reactions, they have not been used for modification of polymers. In this report, lipases were used to determine regioselective modification of ester functions in a telomer of poly(methyl acrylate). The influence of chain length on the extent of transesterification of methyl acrylate telomers of D P n ¯ 6–50 was studied by examining the relationship between the extents of enzymic modification to other telomerization parameters. The regioselectivity was observed when the average D P n ¯ of telomers is in a range of 6–22. At a higher D P n ¯ (>22), however, the average number of reacting ester functions per telomer strongly deviated from the theoretically predicted value. This phenomenon was suspected as a result of steric hindrance caused by folding of longer telomer chains. To verify this hypothesis, acrylate telomers at a D P n ¯ ranging from 10 to 42 were synthesized using a shorter telogen, i.e., 2,2′-ethanedithiol. The transesterification of these telomers showed a deviation in a degree of conversion when D P n ¯ was greater than 10, possibly indicating the inhibition caused by steric hindrance. Therefore, regioselective modification of acrylic polymers, which is difficult to achieve by conventional chemical methods, may be accomplished enzymatically.

This paper describes two different methods, based on the electrochemical reduction of diazonium salts, for the strong binding of polymers to an iron surface. The first method involves the electrochemical reduction, on an iron electrode, of the diazonium salt of 4-aminobenzophenone. This permits the covalent attachment of 4-benzoylphenyl moieties on the surface. Polystyrene (PS) is then deposited on the modified iron surface and can be covalently bonded to the 4-benzoylphenyl groups under irradiation. Another method involves the attachment of carboxyphenyl groups to the iron surface by reduction of the diazonium salt of 4-aminobenzoic acid and the further attachment of poly(1,2-propanediyl fumarate) to the phenylcarboxylate functions through ionic bonds with Mg2+ ions. The barrier properties of the polymeric films are characterized by electrochemistry and by the protection they provide against corrosion.

Enzyme-catalyzed polymer synthesis has gathered many scientists around a major topic such as the synthesis of polyesters by enzyme catalysis. Since the mid 80′s indeed, it is commonly accepted and experimented that lipases in particular are able to catalyze reverse reactions when they are used in organic media (less data are reported on esterases or proteases). Transposed to polymer chemistry, these pioneering results led to the definition of numerous reaction systems leading to the formation of polyesters. Thus AA + BB and AB + AB-type polycondensations as well as lactones and macrolides polymerizations have been achieved in various organic solvents. In this article, the creation of aliphatic, unsaturated and aromatic polyesters is reviewed with a special attention paid to the equilibria between linear chains and rings.

This article describes hybrid materials and systems in which the core integrity of inorganic nanobuilding blocks (NBBs) is preserved and reviews the main synthetic procedures presented in the literature. The relation between the NBB and the resulting hybrid networks is discussed for several striking examples: silicon and tin oxo clusters, polyoxometalates, and transition metal−oxo-based clusters. This approach is extended to nanoparticule-based hybrids. The chemical strategies offered by the coupling of soft chemistry processes and this approach based on functional NBBs allows, through an intelligent and tuned coding, to develop a new vectorial chemistry that is able to direct the assembly of a large variety of structurally well-defined clusters or nanoparticles into complex architectures.

The free-radical polymerization of acrylamide initiated by a redox system (hydrogen peroxide/β-diketone) catalyzed by horseradish peroxidase is studied with emphasis on the control of the molecular weight of the polymer. The case where 2,4-pentanedione (Acac) is used as the β-diketone is particularly examined. It is shown that the concentration of Acac and that of the enzyme readily control the molecular weight of the polymer. The concentration of hydrogen peroxide does not influence the molecular weight to a significant extent except at extreme values for which enzyme degradation or side reactions interfere with the normal enzymatic cycle. The variations of the molecular weight induced by changes in the chemical structure of the β-diketone are attributed to the reactivity toward the enzymatic cycle. The experimental results are rationalized by the use of classical kinetic equations for free-radical polymerization and including the specific expressions of enzymatic catalysis. The tendencies indicated by the theoretical expressions account for the evolutions given by the experimental results.

The transesterification of methyl acrylate telomers by lipase catalysis in toluene at 50°C was investigated. The specificity of the enzymatic catalyst led to modification of the ester functions of peculiar monomer units. Due to the influence of the near-neighbourhood, only the ester functions of the end-groups and those of the monomer units linked to the telogen segment were modified. It was a completely new result with respect to previous work done in our laboratory. The very precise action of the biocatalyst was characterized from the study of the modification of short telomers as models for longer chains. A detailed analysis of these compounds was made by spectrometric measurements, proton NMR spectroscopy, and size exclusion chromatography. The enzymatic modification opens up numerous possibilities for the design of new acrylate polymers according to the structures of the telogen and of the alcohol used in the transesterification.

It has been shown in Part 1 that the transesterification of methyl acrylate telomers by lipase catalysis in toluene at 50°C is a regioselective modification. Indeed, only the ester functions of the end-groups (A and C functions) and those of the monomer units linked to the telogen segment (B function) were modified. The reactivity of the latter was not expected according to data on the specificity of the Rhizomucor miehei lipase, so that has questioned the influence of the telogen structure on the recognition of the B methyl ester by the enzyme. In this article, methyl acrylate telomers were synthesized from new telogens and their modification by lipase catalysis was investigated under the same conditions as in Part 1. The main result is that the B function is still reactive whatever the structure of the incorporated telogen. Further investigations should be done in order to understand the peculiar contribution of the sulphur atom to the regioselective modification of the telomers. A detailed structural a...

The polymerization of acrylamide in water initiated by a horseradish peroxidase-catalyzed redox system is studied. It combines hydrogen peroxide (as the oxidant) and 2,4-pentanedione (as the reductant). Several side reactions leading to the degradation of the enzyme through the formation of compound III are evidenced by polymerization experiments and UV spectroscopy; they can be avoided by adjusting the reactant concentrations. The oxidation of 2,4-pentanedione by a non-enzymic pathway is also detected by 1H NMR. Its main effect is to reduce the concentration of the enol form of 2,4-pentanedione, and hence to modify the initiation rate. From this information, a schematic picture of the reactions involved in the enzyme-catalyzed redox system is drawn, so as to optimize the polymerization conditions.

The synthesis and the swelling properties of two types of hybrid hydrogels have been studied to point out the contribution of cross-linking organic−inorganic aggregates to the network formation and the water absorption. The first type consists of polyacrylamide hydrogels with embedded polyoxotungstates. The second one has been obtained by radical polymerization of acrylamide in the presence of copolymerizable polyoxotungstates above their critical aggregation concentration. As recently reported for polyacrylamide hydrogels with trapped rods, the incorporation of such polyelectrolytes in a neutral network enhances the ability of the hydrogel to absord water. The same observation holds for polyacrylamide hydrogels with trapped polyoxotungstate aggregates. As polymerizable tetrafunctional polyoxotungstates and acrylamide were copolymerized, aggregate-containing hydrogels were obtained. Their swelling properties were found to be in the low range of those of superabsorbent materials and are discussed in relati...

Polyoxotungstates with propyl methacrylate functionalities and ethyl methacrylate were copolymerized in acetonitrile leading to the formation of networks whose swelling properties have been studied in several organic solvents. The polyanions ensure the cross-linking of poly(ethyl methacrylate) chains and are therefore an integral part of the covalent structure of the gels. This synthetic route to achieve the preparation of polyanion-containing polymeric materials differs from those studied up to now.

The copolymerization of acrylamide with the tetrafunctionalized polyanion [gamma-SiW(10)O(36)(RSiO)(4)](4-) (R=C(3)H(6)OC(O)C(Me)=CH(2)), which acts as a cross-linker, is performed in an aqueous dispersion of maghemite (gamma-Fe(2)O(3)) nanoparticles. It results in a magnetic hybrid hydrogel with superabsorption properties (see scheme). The magnetic properties of the nanoparticles enables their mobility inside the network to be estimated and their release during the swelling of the hydrogel to be observed.

Die Copolymerisation von Acrylamid und dem tetrafunktionalisierten Polyanion [γ-SiW10O36(RSiO)4]4− (R=C3H6OC(O)C(Me)=CH2), das als Vernetzungsmittel dient, in einer wasrigen Dispersion von Maghemit(γ-Fe2O3)-Nanopartikeln fuhrt zu einem magnetischen Hybridhydrogel (siehe Schema) mit superabsorbierenden Eigenschaften. Die magnetischen Eigenschaften der Nanopartikel ermoglichen es, die Partikelbeweglichkeit im Innern des Netzes zu bestimmen und die Freisetzung der Partikel wahrend des Quellens des Hydrogels zu verfolgen.

Free-radical polymerization of acrylamide in water at room temperature involves catalysis by horse radish peroxidase to produce radical species from hydrogen peroxide and 2,4-pentanedione through an oxidoreductive pathway. In the presence of the vinylic monomer, initiation takes place, leading to polyacrylamide formation after a long and unreproducible inhibition period. Conversion-time plots are presented, and some kinetic features are compared with results of previous studies of classical acrylamide polymerization.

The hydrolysis of poly(1,2-propanediyl fumarate), poly(1,2-propanediyl phthalate) and poly(1,2-propanediyl fumarate-co-phthalate)s was studied. In the absence of the lipase from Chromobacterium viscosum, all the samples exhibit a weight loss indicating that uncatalyzed hydrolysis and/or solubilization of shortest chains take place. In the presence of the enzyme, the weight loss is much higher except when the sample is poly(1,2-propanediyl phthalate), which means that the enzyme does not catalyze the hydrolysis of the phthalate functions. SEC and 1H-NMR analyses of the hydrolysis residues of copolymers with various aromatic unit contents showed that the weight loss is accompanied by both molecular weight decrease and aromatic content increase. The enzyme specificity was tested on a phthalic model and the results confirmed the assumption of a selective action of the lipase from Chromobacterium viscosum. If the non-specific uncatalyzed hydrolysis is controlled, the selective enzymic degradation of copolyesters will give a good opportunity to study the copolyester sequences by means of hydrolysis residue analysis.

Enzyme-catalyzed synthesis of aliphatic, unsaturated, and semiaromatic polyesters from diesters and diols was carried out in toluene at different temperatures in the presence of supported lipases from Candida antarctica. Whatever the monomer structure, rings were formed concurrently with linear chains except when dimethyl fumarate was used. The yield of cyclics depends on several parameters such as the monomer structure and the initial concentration of the reactive functions and strongly influences the average molar masses of unfractionated samples. Qualitatively, this is a general feature of the ring−chain equilibrium. Once the existence of this equilibrium was shown, the molar cyclization equilibrium constants (K) for aliphatic, unsaturated, and semiaromatic polyesters were determined, and it would appear that the molar distribution of the ringed species obeys the Jacobson−Stockmayer equation (ln K = ln B − 5/2 ln n, where B and n represent a constant and the number of monomer units of each type in the ...

Enzyme-catalyzed synthesis of aliphatic, unsaturated and semi-aromatic polyesters from methyl diesters and diols was carried out in toluene at 60°C in the presence of supported lipases. Whatever the monomer structure, rings were formed concurrently to linear chains excepted when dimethyl fumarate was used. The yield of rings depends on several parameters such as the monomer structure and the initial concentration of the reactive functions and strongly influences the average molar masses of the unfractionated samples. For aliphatic, unsaturated and semi-aromatic polyesters, the molar cyclization equilibrium constants (K) were determined and it would appear that the molar distribution of the ringed species obeys Jacobson-Stockmayer equation: LnK = LnB - 5/2 Lnn, where B and n represent a constant and the number of monomer units of each type in the ring, respectively.

Hydrolytic degradation of poly(1,2-propanediyl fumarate) was carried out in mild experimental conditions using Chromobacterium viscosum lipase as catalyst. The influence of pH, temperature, enzyme concentration, and enzyme inactivation on the initial hydrolysis rate has been analyzed. Enzymatic and chemical processes were compared. This study is an introduction to the enzyme-catalyzed hydrolysis of networks based on unsaturated polyesters. © 1997 John Wiley & Sons, Inc.

The results obtained in Part I relative to the enzyme-catalyzed hydrolysis of poly(1,2-propanediyl fumarate) are applied to the hydrolysis of the networks prepared from this polyester. The weight loss of polyester samples after 14 days of hydrolysis was correlated to the degree of crosslinking (α) determined by differential scanning calorimetry (DSC). In this work, it was shown that the enzyme-catalyzed hydrolysis rapidly takes place on the uncrosslinked polyester chains only, whereas the chemical hydrolysis affected both free and crosslinked chains. The initial hydrolysis rate of the chemical process does not depend on α or on the nature of the chains (free or crosslinked) but it is lower than that of the enzymatic process. © 1997 John Wiley & Sons, Inc.

The lipase-catalyzed synthesis of poly(1,6-hexanediyl maleate-co-fumarate) from 1,6-hexanediol, dimethyl maleate and dimethyl fumarate is described. No secondary reaction involving the double bounds takes place, so that the copolyester composition can be well defined by adjusting the mole fraction of the dimethyl esters in the initial monomer mixture. The average molar masses of the non-fractionated copolyesters depend on the mole fraction of the dimethyl maleate and are correlated with the amount of macrocycles formed. The possibility that the reaction system obeys a ring-linear chain equilibrium is discussed. Linear polyester chains and macrolactones are characterized by 1 H NMR spectroscopy, steric exclusion chromatography and tonometry. A comparison is made with the homopolyester syntheses which were described in previous works.

The enzyme-catalyzed synthesis of poly(1,6-hexanediyl terephthalate) and poly(1,6-hexanediyl isophthalate) is described. An unsuccessfull attempt to synthesize poly(1,6-hexanediyl o-phthalate) is also presented and the reactivity of those three monomers is discussed according to the enzymatic nature of the catalyst. The crude polyesters are characterized by 1H and 13C NMR spectroscopy and by differential scanning calorimetry. Macrocycles are isolated from poly(1,6-hexanediyl isophthalate) and characterized by steric exclusion chromatography and by mass spectrometry. The number-average molar masses and the thermal properties of the crude, linear and cyclic polyesters are also reported.

Enzyme-catalyzed synthesis of aliphatic polyesters in organic media from methyl diesters and diols was carried out at stoechiometric ratio in the presence of supported lipases (li-pozyme® and novozyme®). Two systems were studied to shift the thermodynamic equilibrium which limits the conversion. In the first one, the solution flows through a molecular sieve in which methanol is adsorbed. In the second one, methanol is eliminated by nitrogen bubbling. The system with nitrogen bubbling in hydrophobic solvents at 60°C works best when novozyme® is used as catalyst. Despite a high fractional conversion (p> 0.99), the number-average molar mass is not very high (M;n = 3050 eq. PS). In relation to the nature of monomers, cycles with DP = 2–20 were characterized by chromatographic analyses and mass spectrometry. Their formation explains why high polycondensates cannot be obtained. © 1995 John Wiley & Sons, Inc.

The lipase-catalyzed preparation of poly(1,6-hexanediyl maleate) by transesterification of 1,6-hexanediol and dimethyl maleate is described. A configurationally pure poly(1,6-hexanediyl maleate) exhibiting exclusively cis structure was obtained. During the reaction, a substantial amount of macrolactones was formed. They were isolated, and the cyclic oligomer with y = 2 was found to predominate. Cycles are semi-crystalline, while no melting point was detected for the linear poly(1,6-hexanediyl maleate). We assume that the linear unsaturated polyester is completely amorphous owing to its cis configuration.

Oligo(methylacrylate)s with ester end-group are transesterified by allyl alcohol in the presence of lipozyme as catalyst. The transesterification is regioselective: only end-group is modified. The structure of the modified oligomers is studied by 13C NMR spectroscopy.

A novel initiating system for free-radical polymerization at room temperature has recently been described by our laboratory. It is based on the catalytic properties of horseradish peroxidase (HRP) to generate radical species from hydrogen peroxide and 2,4-pentanedione (acetylacetone) through an oxydoreductive pathway. In the presence of an acrylic monomer (acrylamide), initiation takes place leading to a polymer. The enolic form of acetylacetone is assumed to directly intervene in the catalytic cycle so the question has been raised in order to determine if other β-diketones might play a similar role in HRP-mediated polymerization. Assumptions on the initiation mechanism are discussed in relation to the well-known HRP catalytic scheme.

A butyltin oxo-cluster, {(BuSn)12O14(OH)6}2+, functionalized through electrostatic interactions with two 2-acrylamido-2-methyl-1-propanesulfonate anions (AMPS), has been synthesized and characterized by single crystal X-ray diffraction and multinuclear (1H, 13C and 119Sn) NMR. Its polymerization or co-polymerization with methyl acrylate yield hybrid materials where the nanobuilding blocks are fully preserved and act as nano-fillers and cross-linking agents. According to the electrostatic nature of the cross-linking, these materials can yield gels or solutions depending on the solvent used to swell them.

Hybrid copolymers have been prepared by free radical polymerization, in toluene, of methylacrylate (MA) and varying amounts of an organotin oxo-cluster functionalized with two acrylamido groups, {(BuSn)12O14(OH)6}(AMPS)2. The tin based nanobuilding block is fully preserved in the final materials. These copolymers formed networks where the cross-linking is based on the electrostatic interactions that take place between the macrocation {(BuSn)12O14(OH)6}2 + and its two functional anions (AMPS–). Accordingly, these copolymers can yield gels or solutions depending on the solvent used to swell them.

The polymerization of dimethyl terephthalate and diethylene glycol by enzymic catalysis in toluene is described. The potential pi-pi interactions of the aromatic rings together with the relative flexibility of the diol segment have been regarded as synergy factors responsible for the formation of a pure cyclic compound. The so-called C2 macrocycle was characterized by (1)H and (13)C NMR, size-exclusion chromatography, differential scanning calorimetry, mass spectrometry, and X-ray diffraction on powder. Structurally speaking, it is made of two repeating units. The substitution of the central oxygen atom of the diol by -CH(2)- or -S- as well as the presence of ortho-substituents (-NH(2) or -NO(2)) on the phthalate were expected to disrupt the stacking of the phenyl groups more or less.

The study and uses of enzymes are no longer limited to the domain of biologists.1 Since the mid-1980s, chemists have used more and more of the enormous possibilities of these catalysts, particularly in organic chemistry. Enzymes exhibit a much higher selectivity than classical catalysts. An enzyme catalyzes only one type of reaction, for example hydrolysis, and it recognizes only one compound (the substrate) with a specific structure.

During the Middle Ages and the XVIth century, brazilwood was a red dyewood used in the Western world not only for textile dyeing, but also in painting, especially in manuscript illuminations, as recently shown by physic-chemical analyses. In mediaeval times this material xas imported from Asia, and from the end of the XVth onwards it came from Latin America. This research tries to investigate how in the Middle Ages and in the early modern era brazilwood travelled from such remote areas to Western Europe and could thus be available on the market to European craftsmen and artists. The first part of this study seeks to determine when and how the Medieval West came to know this new material, before analyzing what Europeans knew about this wood and about the tree that produced it. The second part, focusing on Asian brazilwood, identifies production areas in south and south-east Asia, before tracing down the commercial roads followed by this dyewood, first through the Middle East during the Middle Ages, and then from the New World : it defines when and where American brazilwood was produced ; it analyses the conditions of its production and finally considers the specific trade system established by the Spanish and Portuguese Crowns to exploit this natural resource., Le bois de brésil est un bois tinctorial rouge utilisé en Occident à la période médiévale et au XVIe siècle non seulement pour la teinture des étoffes, mais aussi en peinture, en particulier en enluminure, comme l’ont montré des analyses physico-chimiques récentes. Durant le Moyen Âge, ce matériau provient d’Asie, puis, à partir de la fin du XVe siècle, d’Amérique latine. Cette étude a pour objet de comprendre dans quelles conditions, au Moyen Âge et dans les premiers temps de l’ère moderne, le bois de brésil pouvait parvenir de ces régions lointaines jusqu’en Occident et être ainsi disponible sur le marché européen comme matériau colorant pour les artisans et les artistes. La première partie de ce travail s’interroge sur l’époque et les conditions dans lesquelles l’Occident médiéval est entré en contact avec le bois de brésil, puis sur ce que savaient ou non les Européens de ce matériau et de l’arbre qui le produisait. La seconde partie se déplace en Asie pour y identifier les régions productrices du bois tinctorial, retracer son cheminement jusqu’en Occident, d’abord par l’intermédiaire du Proche-Orient arabo-musulman durant la période médiévale, puis par la route du Cap à partir de la fin du XVe siècle. Enfin, la troisième et dernière étape de cette recherche se concentre sur l’Amérique pour déterminer où et comment, à partir de la fin du XVe et au cours du XVIe siècle, ce continent se met à produire du bois de brésil, cerner les modalités de cette production et analyser le type de régime commercial spécifique alors établi par les Couronnes ibériques pour l’exploitation du brésil américain.