Michel Bartholin

Thermal dehydrochlorination and stabilization of poly(vinyl chloride) in solution: Part III—Zn-Ca stearates as stabilizers

Abstract The thermal degradation of poly(vinyl chloride) (PVC) in trichlorobenzene (TCB) solution at 187°C has been studied in the presence of various mixtures of zinc and calcium stearates, using coulometric titration of chloride ions, HCl evolution measurements and spectroscopic analysis (FTIR and UV) of the degraded polymer at various times. The substitution reaction, initially suggested by Frye and Horst1,2 is clearly demonstrated, although the very small amount of stearate groups involved with respect to the number of vinyl chloride units makes it difficult and requires the use of high performance equipment and careful recording conditions. Many of the known features of the stabilization of PVC with mixed metal soaps are also observed. In addition, a transient complex between the metal stearates is observed which cannot be separated from the polymer because it shows the same solubility behavior. Evidence for secondary reactions between metal chlorides and stearic acid is given. Finally, the rates of the processes are very dependent on the amounts of structural defects in the initial polymer.

Catalysts containing supported rhodium complexes. A new support: polyphenylsiloxane on silica

Abstract When silica is coated with an organosilicon ladder polymer, after chloromethylation and phosphination it is possible to obtain a support for catalysts containing rhodium complexes which have proved much more active towards olefin hydrogenation than their homogeneous analogues, although they seem to follow the same general mechanism. The reasons for this new but expected result are discussed and a comparison is made with other similar supported catalysts.

Infrared evidence for the grafting of ester groups on polyvinyl chloride stabilised by Zinc and Calcium stearates

SummaryCareful FTIR analysis of PVC samples heated in trichlorobenzene solution at 187°C in the présence of mixture of zinc and calcium stearates for various times were carried out. A special accessory allowing identical flushing of several samples with dry nitrogen was used. The samples were thoroughly purified before examination. The very weak carbonyl absorption, after an initial decrease, increases as a sharp band near 1734 cm-1 progressively shifting towards lower wave numbers and then decreases with simultaneous broadening. A corresponding C-H band is seen near 2850 cm-1.

Influence of the texture of phosphinated polystyrene resins on the stability and catalytic activity of supported rhodium complexes

Abstract The Cramer complex, Rh2Cl2(C2H4)2, was fixed onto 3polystyrene — co divinylbenzene (DVB) resins previously chloromethylated and phosphinated. The resins differ by their DVB amount and their porosity. The intrinsic catalytic activity versus hexene hydrogenation is dependent not only on the Rh contents, but more significantly on the localization, and then on the availability of the sites, which depends on the preparation process. The changes that are observed after ageing under hydrogen are related to the formation of metallic particles active for benzene hydrogenation. This evolution of the complex strongly depends on the texture of the resin and on the temperature. A tentative explanation is given.

Polyphenylsiloxane and related compounds as supports for hydrogenation catalysts, based on rhodium complexes

Abstract Attempts have been made to understand the high catalytic activity versus olefin hydrogenation of rhodium complexes supported on phosphinated polyphenylsiloxane covering silica. Chloromethylated and phosphinated prepolymer, high polymer and model compounds have been prepared. The basicity of the phosphines is not very much changed by their fixation on a polyphenylsiloxane substrate. Some evidence is presented for a bis-coordination of the rhodium-active sites onto the surface of the support. However, some doubt remains about the actual nature of the active sites owing to an indication of the possible formation of metallic rhodium.

Essais d'isolement de complexes catalytiques dimerisables par fixation sur un support polymere

Abstract Iridium pyridino phosphino complexes extremely active in olefin hydrogenation catalysis, were anchored on highly crosslinked polystyrene—divinyl-benzene macroporous resins carrying well dispersed phosphine groups. Although the catalytic sites are totally dispersed, the catalysts are more or less rapidly deactivated. An alternative cause of deactivation might be a dissociation process followed by dimerization of the dissociated complex.

Versuche zur Rhodium(I)-katalysierten asymmetrischen Hydrierung von α-Acetamidozimtsäure mit monomeren und polymeren Aminophosphinen / Rhodium (I) Catalyzed Asymmetric Hydrogenation of α-Acetamido Cinnamic Acid with Monomeric and Polymeric Aminophosphines

An optically active 1-phosphino-2-aminopropane, prepared from ephedrine, has been used for the Rh(I) catalyzed asymmetric hydrogenation of α-acetamido cinnamic acid. Optical yields up to 77 percent were obtained. Low stereoselectivity has been found using 1,4-bis(diphenylphosphino)-2,5-dibenzylpiperazine and a polystyrene bound bisdiphenyl-phosphine, obtained from phenylalanine. The preparation of optically active piperazines from α-amino acids is reported

Diethynyl terminated siloxane bases (bisazomethine Schiff base)

SummaryBis-4 ethynylbenziminopropyl-hexamethyldisiloxane was prepared and characterized. The flexible central unit of this product allows an easy and thorough polymerization of the ethynyl groups at a moderate temperature.After thermal polymerization of the ethynyl groups, another reaction takes placeupon curing, leading to a product presenting no detectable Tg.This increase in crosslinking could be related to a diene synthesis involving both olefinic and imine double bonds.