A contribution to the study of the catalytic action of clays on the polymerization of styrene: II. Reaction mechanism

Abstract

: The study of 13C NMR spectra of polystyrene thermally obtained on clays shows that thermal polymerization of styrene on these minerals proceeds by two parallel reaction mechanisms: the radical mechanism due to the thermal effect, and the cationic mechanism in which the initiatory cation H + is provided by the clay. The latter mechanism, accelerated by increase in temperature, becomes more important as the clay content increases in the reaction medium. Otherwise, the thermal polymerization on clays is accompanied by the hydrogenation of some g carbons of the polystyrene molecule and the oxidation of certain aromatic carbons.In a previous study, it was shown that mildly acid-treated clays catalyse the thermal polymerization of styrene. The gel permeation chromatograms of the polystyrenes formed revealed the intervention of two polymerization mechanisms (Njopwouo et al., 1987). Heat acts on polystyrene by producing free radicals to start polymerization, and in this case, the radical mechanism is evident. A supplementary polymerization test was carried out at ambient temperature to demonstrate the intervention of the other mechanism; the control tests (without clay), and those with the three clays used in the preceding study showed that at the same clay catalyst concentration P (P = 0.8%), polymerization of styrene started after 3 days on Bo4 (KPIM* mixture), 4 days on Bal (halloysite) and 5 days on Bol (kaolinite) with conversion rates z of 1-9%, 1-5% and 1.0%, respectively. In the control test, polymerization began after 7 days. These results showed that clays could initiate the polymerization of styrene by a non-radical mechanism. A cationic mechanism can be envisaged, and according to Fripiat et al. (1965Fripiat et al. ( , 1971, silico-alumina surfaces possess Lewis and BrSnsted acid sites, the latter being predominant in hydrated silico-alumina (as in clays). In other respects Conley & Althoff (1971) showed that acid-treated kaolinite possesses BrSnsted acid sites (H3 O+) on its surface at low temperature due to silanol groups, and Lewis acid sites (A13+) at high temperature, from the octahedral gibbsitic sheet. In the trials reported, the acid sites, especially Brfnsted style, could be responsible for the cationic polymerization mechanism occurring in parallel with the radical mechanism. The present study is aimed at confirming the presence of these two mechanisms from observations on ~3C nuclear magnetic resonance (NMR).* KPIM --kaolinite-palygorskite-illite-montmorillonite.9 1988 The Mineralogical Society

Talc indices from Boumnyebel (Central Cameroon), physico-chemical characteristics and geochemistry

“…Physico-chemical and beneficiation studies of clay materials in Cameroon have been carried out on kaolinite, illite, montmorillonite, palygorskite and beidellite (Njopwouo, 1984;Njopwouo et al, 1987Njopwouo et al, , 1988Elimbi and Njopwouo, 2002) but not on talc. Though talc occurrences are rare in Cameroon, two occurrences of talc-rich rocks are reported at Baoina and Mayo Boula in North Cameroon (Laplaine, 1969).…”

Synthesis and Characterization of Polymeric Material Consisting on Acrylamide Catalyzed by Maghnite (Algerian MMT) under Microwave Irradiation

“…Figures 5 and 6 show the FTIR spectra for the final product and the monomer. The peaks at 3191-3331 cm −1 were due to amine group, whereas, the absorption peak at 1651 cm −1 is strong and sharp and is attributed to the carbonyl (C〓O) of the carboxyl group [38]. The peaks at 2868.68 and 2909.55 and 2931.10 cm −1 are assigned to υ-CH 2 [39].…”

Silica-alumina catalysts for polymerization of cyclic siloxanes

“…NMR spectra were recorded using a Bruker ACP 200 spectrometer in CDCl 3 . IR spectra were re- the mobile phase.…”

“…Aluminosilicates, natural or synthetic, could Polymerization of cyclic siloxane monomers is serve as environmentally friendly catalysts used generally carried out using acidic and basic catafor polymerization/oligomerization of alkenes. [2][3][4][5][6] lysts. 1 Catalysts that have been reported to initiPike patented a method of polycondensation of ate cationic polymerization of siloxane include silanol oligomer to give high molecular weight orprotonic acids like H 2 SO 4 , HClO 4 , a variety of ganosilicon polymer using zeolite.…”