Ernest Maréchal

Study of model esterifications and of polyesterifications catalyzed by various organometallic derivatives—I. Study of esterifications catalyzed by titanium derivatives

Abstract We compared the efficiencies of several esterification catalysts. The esterification of octadecanoic acid in octadecanol, catalyzed by organotitanium derivatives is studied as a polyesterification model. Ti(OBu) 4 activity does not depend on [COOH] 0 and remains unchanged during the whole reaction. the influence of pressure and of the nature of the alcohol and of the titanium ligands is studied. It is unambiguously shown that the catalysis is effective only when titanium ligands and alcohol ROH can be exchanged; when this exchange is possible, the catalytic efficiency does not depend on the nature of the initial ligands provided that R is not too bulky.

Study of model esterifications and of polyesterifications catalyzed by various organometallic derivatives—III. Kinetic and mechanistic study of eterifications catalyzed by tetrabutoxytitanium or zirconium

Abstract The kinetics of the esterification of octadecanoic acid in 1-octadecanol under 14 mmHg in the presence of either Ti(OnBu) 4 or Zr(OnBu) 4 are studied at various temperatures. It is shown that mechanisms taking only acid and alcohol into consideration do not account for experimental data. More complicated mechanisms are examined: existence of an equilibrium between the catalyst and the reaction species or successive and simultaneous reactions of the catalyst; the latter gives the more satisfactory results. A reaction scheme is proposed.

Lipozyme-catalyzed transesterification of oligo(methylacrylate)s

SummaryOligo(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.

Synthesis and characterization of new methyl-substituted azomethine-siloxane liquid crystal macrocycles

SummaryThis article is devoted to the synthesis of new methyl-substituted azomethine-siloxane macrocyclic dimers. They have been obtained by an intramolecular interiminination reaction of linear polydimethylsiloxane-block-polyazomethine main-chain liquid crystal polymers. The reaction has been studied on mono-, di- and tetramethyl-substituted azomethine moities to estimate the influence of methyl-substitution on the feasibility of the reaction. Specific conditions (diluted solution, strong acid catalysis, recrystallization) led to pure macrocyclic dimers, which have been characterized by SEC, 13C NMR and X-ray crystallography. This reactional process is the first step for synthesis of substituted liquid crystal macrocyclic structures, which constitute a new family in the liquid crystal polymer field.

Cationic polymerization of isobutylene initiated by diol/boron trichloride systems

Cationic polymerizations of isobutylene initiated by 2,5-dimethyl-2,5-hexane diol (HMD) and bis-para-2-hydroxy-2-propylbenzene (BPP)/BCl3 were carried out in CH2Cl2 solution at −30 °C, in presence or in absence of 2,6-ditert-butylpyridine (DtBP).IR, 1H NMR and C13 NMR analysis of the resulting polyisobutylenes (PIB) show the insertion of the diol skeleton in the polymers. GPC chromatograms show that the presence of DtPB prevents protonic initiation. The synthesis of PIB with phenolic end groups was carried out by alkylation of α, ω unsaturated oligoisobutylene in CH2Cl2 at −30 °C initiated by SnCl4. Previously,the alkylation was carried out on a model:2,2,4-trimethyl pentene (TMP). Spectroscopic analyses show that the alkylation takes place mainly on para-position. UV titration of phenyl ring and chemical titration of chlorine show that the functionality of PIB is 2.

A possible “direct initiation” of cationic polymerization of isobutylene by boron trichloride in methylene chloride

SummaryInitiation of the cationic polymerization of isobutylene by BCl3 requires a cocatalyst in most cases. However, we found conditions (θ=-30°C, CH2Cl2 as solvent, BCl3 ⩾ 0.0l m) where a direct initiation by BCl3 (i.e. with no cocatalyst) is possible. We showed that in such conditions HCl is not a cocatalyst and that H2O content is too low to explain the results (high vacuum and highly purified reactants and solvent).The conversion increases linearly with tine increasing concentration of BCl3.A mechanism is proposed.

Study of model esterifications and of polyesterifications catalyzed by various organometallic derivatives—II. Study of esterifications and polyesterifications catalyzed by zirconium derivatives

Abstract The esterification of octadecanoic acid in 1-octadecanol catalyzed by zirconium derivatives is studied. The catalytic efficiency does not depend on [COOH]0 and does not change during the esterification. Reactions carried out at 760, 100 or 50 mmHg are characterized by autoacceleration which is not observed when pressure is 14 mmHg. The dependence of the catalytic efficiency on the nature of the zirconium ligands is studied as well as the behaviour of the system when water is added in various experimental conditions. The polycondensation of oligo (1,6-hexanediyl adipate) and of oligo (1,10-decanediyl adipate) is studied in the absence of catalyst or in the presence of tetrabutoxyzirconium.

Chemical modification of chlorinated rubbers—III. Quantitative study of the grafting of chlorinated rubber by aminoesters and versamids

Abstract A quantitative study of the grafting of chlorinated rubber by ethyl 11-aminoundecanoate is carried out. A self-condensation of the aminoester takes place during the grafting; its extent is determined. The grafting of CR by versamid 100 (acetylated or not) is studied quantitatively by several analytical methods (i.r., 1H- and 13C-NMR) and they are compared with respect to accuracy. Non-crosslinked versamid-grafted-chlorinated rubber is obtained.