Monomer gravimetric determination

This procedure is based on the measurement of the contraction of volume that results from the different densities of the monomer and polymer. The conversion of the volume contraction to the yield of polymer can be made by means of a gravimetrically determined calibration curve or by calculation from the specific volumes (see Example 3-6). 

Of the four-coordinate complexes of Ni those with the square planar stereochemistry are the most numerous. They include the yellow [Ni(CN)4] , the red bis(A(-methyl-salicylaldiminato)nickel(ll) and the well-known bis(dimethylglyoximato)nickel lI) (Fig. 27.6b and c) obtained as a floccuicnt red precipitate in gravimetric determinations of nickel. Actually, in the solid state, this last compound consists of planar molecules stacked above each other. so that Ni-Ni interactions occur (Ni-Ni 325 pm), and the nickel atoms should therefore be described as octahcdrally coordinated. However, in non-coordinating solvents it dissociates into the square-planar monomer, while in bis-(ethylmethylglyoximato)nickel(Il) a much longer Ni Ni separation (475 pm) indicates that even in the solid it must be regarded as square planar. 

At room temperature and atmospheric pressure, vinyl chloride is a gas, albeit a readily condensable one. At ambient temperatures, the solubility of PVC in the monomer (by direct gravimetric determination) is 0.03% [37], although the literature states elsewhere that at about 0.5% conversion of vinyl chloride, precipitation of the polymer is noted [36]. 

Other reported NIRS applications are the determination of micro-additives in PP pellets [260], of additive levels in masterbatches or shipments, of plasticisers in PVC, of moisture content in polyalky-lene glycol ethers [292], of rest monomer in polymers (e.g. PPO) [278], On-line monitoring of the moisture and lubricant levels on polyacetate fibre film using NIR reflectance measurement was reported [293], NIRS allows rapid identification of polymer dispersions and an accurate water content determination ( 0.2%). The method replaces the tedious gravimetric determination of the non-volatile solid content of dispersions according to DIN 53189. 

The same equation applies in a 3-component system containing diluent at constant mole fraction of diluent. Therefore, pressure drop can be related to conversion, if data on the partial molal properties of monomer and polymer and the compressibility of the mixture axe available. Since such data are unavailable, conversion must be obtained by sampling and gravimetric determinations of yield or by means of a previously established calibration of 3deld vs. pressure drop 34). 

Procedures. A standard recipe for the latex preparation is shown below (St + M2) 20 g, (water + buffer) 160 g, and initiator 5 mmole/1. The weight fraction of M2 in monomer charge (f) was varied from 0.01 to 0.50. Polymerizations were carried out at 55°C or 70°C and pH 2.5 or 9.0 under nitrogen. Samples were withdrawn from the reaction mixture at various time intervals and the polymer was precipitated in an excess of acetone. The conversion and polymer composition were determined by gravimetric means and by elemental analysis, respectively. The M2 fraction in instantaneously-formed copolymer ( Fi ) was calculated from eq. 1 ... 

The polymer was isolated by evaporation of the unconverted monomer and the conversion determined gravimetrically. 

More recently Saegusa et al. [120, 45] have developed a technique for the determination of the concentration of active centres, [P l, by terminating the polymerization with the sodium salt of phenol, Na OPh , and estimating the PhO-groups in the polymer spectrophoto-metrically. A closely related method has been used by Jaacks et al. [121] to estimate the concentration of tertiary ox onium ions in the polymerization of 1,3 dioxolan (Section 7.3). Saegusa has shown that the chromophore polymer—OPh has an absorption maximum, X iax 272 nm and an extinction coefficient, e, = 1.96 x 10 1 mole cm in methylene chloride. Consumption of monomer as a function of time was followed by a gravimetric method and the results interpreted [122] according to the kinetic scheme. 

The polymerization kinetics were studied via time-conversion relationships at different dose rates (Figures 6-9). The radiation curing was carried out at room temperature in closed aluminum capsules. Percent monomer conversion was determined gravimetrically for N-vinylpyrrolidone. Evaporation was accomplished under vacuum in a ventilated oven at 50 °C until the weight was constant. For butyl methacrylate and polyester resins, the residual monomer content was determined by gas chromatographic analysis after immersion of the cured products in acetone. 

Monomer Conversion. Off-line methods such as gravimetric analysis and gas chromatography as well as several online methods can be used to determine monomer conversion throughout polymerization [116, 138, 149, 189-195],... 

Internal grafting of tubes (4 mm and 6 mm I.D.) was performed by pumping the monomer (or monomer solution) through the tubes for different lengths of time and irradiating the preswollen tubes in a Co-Y-source with a dose rate of 1 J kg s (= 3.6 105 rad h ). After extraction with an EtOH/water mixture and pure water, the grafting yield was determined gravimetrically. 

The conversion of the polymerization reaction was determined gravimetrically. About 1.5 g of the polymer-monomer mixture was weighed precisely and solved in acetone. A small amount of hydroquinone was added to this solution to prevent further polymerization on heating. 

The product of this polymerization is applied in specialty areas, such as the manufacture of recording tapes and toners for photocopiers. When styrene (St) and butylmethacrylate (BMA) are mixed in the molar ratio 1 1, the polymer formed is transparent and has a glass transition temperature of about 30°C. Figure 8.3 shows the two monomers. The conversion in this case is measured gravimetrically. The product was dissolved in THF, and a small amount of hydroquinone was added to inhibit further reaetion. The molecular weight distribution was determined by gel permeation ehromato-graphy (GPC) with two mixed columns of polymer laboratories. The detection method used was by reactive index. 

Conversion versus dose curves have been determined for a number of diyne surfactants in the bulk crystalline state, after exposing the crystals to penetrating °Co- y-irradiation. Conversion data were obtained gravimetrically by weighing the amount of insoluble polymer subsequently to solvent extraction of residual monomer from the crystals. 

The yield of the copolymeric microspheres was determined gravimetrically. After copolymerization, the latex solution was added to 1% calcium chloride solution and centrifuged to isolate the particles from the mixture. The copolymeric microspheres were washed several times successively with water and methanol solvents to remove the remaining monomer and initiator, and then dried in a vacuum oven at 50 °C till attainment of constant weight. The conversion of monomers was calculated by the equation (3)... 

Cationic latex particles with surface amino groups were prepared by a multi-step batch emulsion polymerisation. Monodisperse cationic latex particles to be used as the seed were synthesised first. Then the amino-functionalised monomer, aminoethylmethacrylate hydrochloride, was used to synthesise the final functionalised latex particles. Three different azo initiators were used 2,2 -azobisisobutyramidine dihydrochloride, 2,2 -azobisdimethyleneisobutyramidine dihydrochloride, and 2,2 -azobisisobutyronitrile. Hexadecyltrimethylammonium bromide was used as the emulsifier. The latices were characterised by photon correlation spectroscopy to study the mean particle diameters, transmission electron microscopy to deteimine the particle size distributions, and hence the number- and weight-average diameters and the polydispersity index. The conversion was determined gravimetrically, the surface density of the amino groups was detemiined by conductimetric titrations, and the... 

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