Vierte Schwebstofftechnische Arbeitstagung in Mainz am 29. und 30. September 1955

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Stereospecific polymerization of isobutyl vinyl ether. III. Polymerization with VCl3 • LiCl

The polymerization of isobutyl vinyl ether by vanadium trichloride in n-heptane was studied. VCl₃ ? LiCl was prepared by the reduction of VCl₄ with stoichiometric amounts of BuLi. This type of catalyst induces stereospecific polymerization of isobutyl vinyl ether without the action of trialkyl aluminum to an isotactic polymer when a rise in temperature during the polymerization was depressed by cooling. It is suggested that the cause of the stereospecific polymerization might be due to the catalyst structure in which LiCl coexists with VCl₃, namely, VCl₃ ? LiCl or VCl₂ ? 2LiCl as a solid solution in the crystalline lattice, since VCl₃ prepared by thermal decomposition of VCl₄ and a commercial VCl₃ did not produce the crystalline polymer and soluble catalysts such as VCl₄ in heptane and VCl₃ ? LiCl in ether solution did not yield the stereospecific polymer. It was found that some additives, such as tetrahydrofuran or ethylene glycol diphenyl ether, to the catalyst increased the stereospecific polymerization activity of the catalysts. Influence of the polymerization conditions such as temperature, time, monomer and catalyst concentrations, and the kind of solvent on the formed polymer was also examined.     

Enthalpie der Polymerisation von 7-Oxabicyclo[2.2.1]-heptan sowie exo- und endo-2-Methyl-7-oxabicyclo-[2.2.1]-heptan

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Cationoid living polymerisations

The cationoid living polymerisations have many of the characteristics of pseudo-cationic (φ-cat) polymerisations and none of those of cationic polymerisations. In contrast to the φ-cat polymerisations by protonic acids, which are transfer-dominated, those giving living polymerisations are propagated by esters which are part of a donor-acceptor complex involving a “third reagent”. There are three types: The first is exemplified by an ester which is activated by a metal halide, e.g. HMI (from monomer M + HI) + ZnBr₂, or oligoisobutyl acetate + BCl₃. The second type is exemplified by a polymer triflate complexed by a dialkyl sulphide. The reagents which change the reactivity of the ester are termed “modifiers”. The acceptors, e.g. ZnBr₂, which co-ordinate to a donor group on the polymer, are positive modifiers (or activators). The donors, such as R₂S, which coordinate onto an acceptor group at the end of the polymer, e.g. the acidic β-H, are negative modifiers (or moderators). The propagation by both types of modified ester probably involves a 6-centred cyclic transition state. The same applies to a third type of φ-cat propagation, in which a polymeric ester reacts with a D-A complex formed from M + I₂. The formation of unwanted non-living polymers of high DP and/or broad DPD, together with those resulting from living polymerisations, happens because the metal halides used in these reactions not only form the φ-cat propagating centres, but also react with ionogenic impurities to initiate concurrent, short-lived cationic polymerisations. These parasitic reactions can be suppressed by an excess of base, e.g. an ester or halide ions, which scavenge protons and carbenium ions. This phenomenon indicates that, whatever else is propagating the living polymerisations, it is unlikely to be carbenium ions. The kinetic equations for the living polymerisations, developed here, make it possible to calculate propagation rate-constants from rate and DP data; such calculations are shown for a variety of published results.