Polymerisation stereospecifique du sulfure de propylene en phase homogene

The homogeneous polymerization of propylene sulphide, initiated by cadmium or zinc thiolates, proceeds without important termination reactions and gives “living” polymers. The molecular weight distributions of the polymers are narrow. After elimination of the metal included in macromolecules, changes of molecular weight are not observed. Zinc or cadmium atoms are not located in the middle of the chains but at one end. Different types of associations are shown by viscometric studies on living polymer solutions. It is possible to prepare stereoregular polypropylene sulphides from cadmium thiolates in benzene, tetrahydrofuran or tetrahydrothiophene solutions.     

Structure electronique de silacyclopentenes-2 et -3

Photoelectron spectroscopy is used to compare the electronic structures of 1,1′-dimethylsilacyclopent-3-ene, 1,1′-dimethylsilacyclopent-2-ene and several phenyl, vinyl and allyl derivatives. When a π orbital is on α position of the silicon atom, a hyperconjugation (α(SiC)π interaction) and a homoconjugation (p_πd_π interaction) are observed. The polarization induced by the P_πd_π interaction explains the differences of nucleophilic reactivity showed by the compounds studied. Also, the analysis of the shifts of first ionization potentials made it possible to propose a conformation for 1,1′-diallylsilacyclopent-3-ene.