Initiator dosage in the solid phase during the suspension polymerization of vinyl chloride has been investigated with the use of a special apparatus developed for this purpose. Results arc reported on a series of polymerizations in which the initiator was divided in various ratios between the starting and additional quantities, added either in one dose or repeatedly to the reaction mixture at various reaction times. Discussed is the kinetic course of polymerization and the effect of dosage on the rate of reaction heat release. It is found for the system used that a suitable dosage regime allows the total amount of the initiator to be reduced by as much as 15 percent, while the yield and the reaction time corresponding to the standard polymerization procedure remain unchanged.
AbstractŠtěpite, tetragonal U(AsO3 OH)2(H2O)4 (IMA 2012-006), is the first natural arsenate of tetravalent uranium. It occurs in the Geschieber vein, Jáchymov ore district, Western Bohemia, Czech Republic, as emerald-green crystalline crusts on altered arsenic. Associated minerals include arsenolite, běhounekite, claudetite, gypsum, kaatialaite, the new mineral vysokýite (IMA 2012-067) and a partially characterized phase with the formula (H3O)+2(UO2)2(AsO4)2˙6H2O. Štěpite typically forms tabular crystals with prominent {001} and {010} faces, up to 0.6 mm in size. The crystals have a vitreous lustre and a grey to greenish grey streak. They are brittle with an uneven fracture and a very good cleavage on (001). Their Mohs hardness is about 2. Štěpite is not fluorescent in either short-wave or long-wave ultraviolet light. It is biaxial (–) with refractive indices (at 590 nm) of α = 1.636(2), β = 1.667(3), γ = 1.672(2) and 2Vobs < ~5°, anomalous greyish to pale yellow interference colours, and no pleochroism. The composition is as follows: 0.12Na2O, 50.19 UO2, 0.04SiO4, 0.09 P2O5, 0.93 As2O5, 1.95 SO3, 16.41 H2O; total 107.90 wt.%, yielding an empirical formula (based on 12 O a. p. f. u.) of (U1.01Na0.02)Σ1.03[(AsO3OH)1.82 (PO3OH)0.04(SO4)0.13(SiO4)0.01]Σ 2.00˙4H2O. Štěpite is tetragonal, crystallizing in space group I41/acd, with a = 10.9894(1), c = 32.9109(6) Å, V = 3974.5(1) Å3, Z = 16 and Dcalc = 3.90 g cm-3. The six strongest peaks in the X-ray powder-diffraction pattern [dobs in Å (I) (hkl)] are as follows: 8.190(100)(004), 7.008(43)(112), 5.475(18)(200), 4.111(16)(008), 3.395(20)(312,217), 2.1543(25)(419). The crystal structure of šteěpite has been solved from singlecrystal X-ray diffraction data by the charge-flipping method and refined to R1 = 0.0353 based on 1434 unique observed reflections, and to wR2 = 0.1488 for all 1523 unique reflections. The crystal structure of štšpite consists of sheets perpendicular to [001], made up of eight-coordinate uranium atoms and hydroxyarsenate 'tetrahedra'. The ligands surrounding the uranium atom consist of six oxygen atoms which belong to the hydroxyarsenate groups and two oxygen atoms which belong to interlayer H2 O molecules. Each UO8 polyhedron is connected to five other U polyhedra via six AsO3OH groups. Adjacent electroneutral sheets, of composition [U4+(AsO3OH)22-]0, are linked by hydrogen bonds involving H2 O molecules in the interlayers and OH groups in the sheets. The new mineral is named in honour of Josef Štěp (1863–1926), a Czech mining engineer and 'father' of the world's first radioactive spa at Jáchymov.
The emulsion copolymerization of vinyl chloride and butyl acrylate initiated by ammonium peroxodisulfate at 60°C in the presence of an anionic emulsifier was investigated. Random copolymers of butyl acrylate and vinyl chloride covering several sets of monomer compositions were synthesized by emulsion copolymerization conducted to both low and high conversions. The rate of butyl acrylate polymerization at medium conversion was found to be proportional to the 0,5 and 1,0 power of the butyl acrylate concentration for the system with and without vinyl chloride. The overall rate of poymerization was found to decrease with increasing vinyl chloride concentration in the monomer feed. The particle size increases with increasing vinyl chloride monomer concentration in the monomer feed and conversion. The decrease in molecular weight of butyl acrylate/vinyl chloride copolymer is accompanied with the incease of vinyl chloride concentration in the monomer feed and of conversion. The results are discussed in terms of radical desorption, particle nucleation and the dependence of the equilibrium monomer concentration on the reactor pressure. 0 1992, Hiithig & Wepf Verlag, Basel CCC 0025-1 16X/92/$05.00
SynopsisThe conversion curve of the copolymerization of vinyl chloride with propene and the conversion curves of both monomers were determined, their initial reaction rates compared, and the copolymerization parameters determined by a method which utilizes periodical sampling of a heterogeneous reaction mixture from the reactor during the reaction and gas-chromatographic determination of unreacted monomers contained in the sample. The agreement between the final conversion values determined chromatographically and gravimetrically was evaluated by using results of a series of copolymerizations of vinyl chloride containing various amounts of propene in the initial monomeric mixture (5-30 w t 7%) carried out under the same conditions.
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