Styrenes medium

A was in fact observed in both systems (Figure 4). The spectrum for TI was broad probably due to the aggregation (association) of TT in the styrene medium, and that for BHT was clearly split into four peaks (1 3 3 1 ratio hypersplitting constant an = 11.20 G) by the methyl group at the para position and further split into three peaks (1 2 1 ratio oh = 1-67 G) by the protons at the meta positions. In these experiments, we used a large amount (100-200 mM) of the catalyst to... 

Two mechanisms have been proposed in the literature to account for the interaction of polyester and magnesium oxide in the reactive monomer (e.g., styrene) medium. One is a chain extension mechanism and the second is the formation of a coordinate complex, also known as two-stage thickening mechanism [28]. The common starting point for these two mechanisms is the formation of basic and neutral salts with the polyester carboxylic acid (—COOH) end groups according to the following reactions ... 

At low latex soHds-to-pulp ratios, ie, 10—20 pph, latex is added to the beaten pulp to give a paper web with superior web strength, elongation, bursting strength, internal bond, and tear strength. The nitrile latices and medium styrene—butadiene are commonly used as beater additions. In a similar manner, latex can be deposited on asbestos fibers. Such compositions are used as gaskets, linoleum bases, etc. 

Microbiological Oxidation. Styrene [100-42-5] can be oxidized to PEA by aerobic cultuting with a Pseudomonas bacterium ia the appropriate medium (101). Eor a medium containing peptone, (NH 2 04, Na2HP04 12H20, KH2PO4, MgSO and com steep Hquor, the yield is 2.34 mg/mL. 

Bead Polymerization Bulk reaction proceeds in independent droplets of 10 to 1,000 [Lm diameter suspended in water or other medium and insulated from each other by some colloid. A typical suspending agent is polyvinyl alcohol dissolved in water. The polymerization can be done to high conversion. Temperature control is easy because of the moderating thermal effect of the water and its low viscosity. The suspensions sometimes are unstable and agitation may be critical. Only batch reaciors appear to be in industrial use polyvinyl acetate in methanol, copolymers of acrylates and methacrylates, polyacrylonitrile in aqueous ZnCh solution, and others. Bead polymerization of styrene takes 8 to 12 h. 

Suspension polymerisation of styrene is widely practised commercially. In this process the monomer is suspended in droplets 5 -Min. in diameter in a fluid, usually water. The heat transfer distances for the dissipation of the exotherm are thus reduced to values in the range s-fisin. Removal of heat from the low-viscosity fluid medium presents little problem. The reaction is initiated by monomer-soluble initiators such as benzoyl peroxide. 

Property Units G.P. polystyrene Medium-impact PS-SBR blend Very high impact PS-SBR blend Styrene acrylonitrile Medium impact ABS High impact ABS MBS... 

Producing a polystyrene (PS)-DVB copolymer of increasing porosity has been accomplished by dissolving 50-80% styrene, 10-50% divinylbenzene, and 30-70% of an inert organic liquid. Toluene is a solvent for the monomer but is a nonsolvent for the polymerized polymer. The monomer solution is then incorporated into water to form a dispersion of oil droplets followed by the polymerization of the suspended oil droplets from the aqueous medium into the polymer (21). 

Monosized polystyrene particles in the size range of 2-10 /am have been obtained by dispersion polymerization of styrene in polar solvents such as ethyl alcohol or mixtures of alcohol with water in the presence of a suitable steric stabilizer (59-62). Dispersion polymerization may be looked upon as a special type of precipitation polymerization and was originally meant to be an alternative to emulsion polymerization. The components of a dispersion polymerization include monomers, initiator, steric stabilizer, and the dispersion medium... 

Based on the Smith-Ewart theory, the number of latex particles formed and the rate of polymerization in Interval II is proportional with the 0,6 power of the emulsifier concentration. This relation was also observed experimentally for the emulsion polymerization of styrene by Bartholomeet al. [51], Dunn and Al-Shahib [52] demonstrated that when the concentrations of the different emulsifiers were selected so that the micellar concentrations were equal, the same number of particles having the same size could be obtained by the same polymerization rates in Interval II in the existence of different emulsifiers [52], The number of micelles formed initially in the polymerization medium increases with the increasing emulsifier concentration. This leads to an increase in the total amount of monomer solubilized by micelles. However, the number of emulsifier molecules in one micelle is constant for a certain type of emulsifier and does not change with the emulsifier concentration. The monomer is distributed into more micelles and thus, the... 

The free radical initiators are more suitable for the monomers having electron-withdrawing substituents directed to the ethylene nucleus. The monomers having electron-supplying groups can be polymerized better with the ionic initiators. The water solubility of the monomer is another important consideration. Highly water-soluble (relatively polar) monomers are not suitable for the emulsion polymerization process since most of the monomer polymerizes within the continuous medium, The detailed emulsion polymerization procedures for various monomers, including styrene [59-64], butadiene [61,63,64], vinyl acetate [62,64], vinyl chloride [62,64,65], alkyl acrylates [61-63,65], alkyl methacrylates [62,64], chloroprene [63], and isoprene [61,63] are available in the literature. 

Recently, Smigol et al. [75] extensively studied emulsifier-free emulsion polymerization of different monomers including styrene, methyl methacrylate, and glycidyl methacrylate in an aqueous medium by using potassium peroxydisulfate as the initiator. In this study. 

The same PVP series were also tried for the dispersion polymerization of styrene in the ethanol medium by using AIBN as the initiator and aerosol OT as the costabilizer [84]. PVP K-15 usually yielded polymeric particles with a certain size distribution and some coagu-lum. The uniform products were obtained with PVP K-30 and PVP K-90 in the presence of the costabilizer. The tendencies for the variation of the final particle size with the stabilizer concentration and with the molecular weight of the stabilizer were consistent with those obtained for the dispersion polymerization of methyl methacrylate [84],... 

Paine et al. [99] tried different stabilizers [i.e., hydroxy propylcellulose, poly(N-vinylpyrollidone), and poly(acrylic acid)] in the dispersion polymerization of styrene initiated with AIBN in the ethanol medium. The direct observation of the stained thin sections of the particles by transmission electron microscopy showed the existence of stabilizer layer in 10-20 nm thickness on the surface of the polystyrene particles. When the polystyrene latexes were dissolved in dioxane and precipitated with methanol, new latex particles with a similar surface stabilizer morphology were obtained. These results supported the grafting mechanism of stabilization during dispersion polymerization of styrene in polar solvents. 

We have also examined the effect of stabilizer (i.e., polyacrylic acid) on the dispersion polymerization of styrene (20 ml) initiated with AIBN (0.14 g) in an isopropanol (180 ml)-water (20 ml) medium [93]. The polymerizations were carried out at 75 C for 24 h, with 150 rpm stirring rate by changing the stabilizer concentration between 0.5-2.0 g/dL (dispersion medium). The electron micrographs of the final particles and the variation of the monomer conversion with the polymerization time at different stabilizer concentrations are given in Fig. 12. The average particle size decreased and the polymerization rate increased by the increasing PAAc concentra-... 

Paine et al. [85] extensively studied the effect of solvent in the dispersion polymerization of styrene in the polar media. In their study, the dispersion polymerization of styrene was carried out by changing the dispersion medium. They used hydroxypropyl cellulose (HPC) as the stabilizer and its concentration was fixed to 1.5% within a series of -alcohols tried as the dispersion media. The particle size increased from only 2.0 /itm in methanol to about 8.3 /itm in pentanol, and then decreased back to 1 ixm in octadecanol. The particle size values plotted against the Hansen solubility parameters... 

Almog et al. [80] studied the dispersion polymerization of styrene in different alcohols as the continuous medium by using AIBN and vinyl alcohol-vinyl acetate copolymer as the initiator and the stabilizer, respectively. Their results showed that the final particle size decreased with the alcohol type according to the following order ... 

Okubo et al. [87] used AIBN and poly(acrylic acid) (Mw = 2 X 10 ) as the initiator and the stabilizer, respectively, for the dispersion polymerization of styrene conducted within the ethyl alcohol/water medium. The ethyl alcohol-water volumetric ratio (ml ml) was changed between (100 0) and (60 40). The uniform particles were obtained in the range of 100 0 and 70 30 while the polydisperse particles were produced with 35 65 and especially 60 40 ethyl alcohol-water ratios. The average particle size decreased form 3.8 to 1.9 /xm by the increasing water content of the dispersion medium. 

We have studied the effect of monomer concentration in the dispersion polymerization of styrene carried out in alcohol-water mixtures as the dispersion media. We used AIBN and poly(acrylic acid) as the initiator and the stabilizer, respectively, and we tried isopropanol, 1-butanol, and 2-butanol as the alcohols [89]. The largest average particle size values were obtained with the highest monomer-dispersion medium volumetric ratios in 1-butanol-water medium having the alcohol-water volumetric ratio of 90 10. The SEM micrographs of these particles are given in Fig. 15. As seen here, a certain size distribution by the formation of small particles, possibly with a secondary nucleation, was observed in the poly-... 

Figure 16 The variation of the monomer conversion by the polymerization time at different monomer to dispersion medium ratios in the dispersion polymerization of styrene. Monomer/dispersion medium (mL/mL) (a) 5/100, (b) 10/ 100, (c) 20/100. The original SEM photographs were taken with 2600 X, 2(KX) x, and 2600 x magnifications for (a), (b), and (c), respectively, and reduced at a proper ratio to place the figure. (From Ref. 93. Reproduced with the permission of John Wiley Sons, Inc.)...

Lu et al. [86] also studied the effect of initiator concentration on the dispersion polymerization of styrene in ethanol medium by using ACPA as the initiator. They observed that there was a period at the extended monomer conversion in which the polymerization rate was independent of the initiator concentration, although it was dependent on the initiator concentration at the initial stage of polymerization. We also had a similar observation, which was obtained by changing the AIBN concentration in the dispersion polymerization of styrene conducted in isopropanol-water medium. Lu et al. [86] proposed that the polymerization rate beyond 50% conversion could be explained by the usual heterogenous polymer kinetics described by the following equation ... 

Styrene monomer was also copolymerized with a series of functional monomers by using a single-step dispersion copolymerization procedure carried out in ethanol as the dispersion medium by using azobisizobu-tyronitrile and polyvinylpyrollidone as the initiator and the stabilizer, respectively [84]. The comonomers were methyl methacrylate, hydroxyethyl acrylate, metha-crylic acid, acrylamide, allyltrietoxyl silane, vinyl poly-dimethylsiloxane, vinylsilacrown, and dimethylamino-... 

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