Suspension polymerization of vinyl chloride

Wheieas the BPO—DMA ledox system works well for curing of unsaturated polyester blends, it is not a very effective system for initiating vinyl monomer polymerizations, and therefore it generally is not used in such appHcations (34). However, combinations of amines (eg, DMA) and acyl sulfonyl peroxides (eg, ACSP) are very effective initiator systems at 0°C for high conversion suspension polymerizations of vinyl chloride (35). BPO has also been used in combination with ferrous ammonium sulfate to initiate emulsion polymerizations of vinyl monomers via a redox reaction (36). 

Fig. 3-20 Typical polymerization vessel for suspension polymerization of vinyl chloride. After Brydson [1999] (by permission of Butterworth-Heinemann and Elsevier, Oxford).

Materials. The polymer samples were prepared either by physical blending of PVC with an EVA copolymer or by suspension polymerization of vinyl chloride with the EVA copolymer dissolved in the monomer. The resulting dried polymer samples were blended with additives (organic Ba-Cd stabilizer and Pb-stearate) to the following general composition ... 

The majority of PVC is produced by free-radical suspension polymerization of vinyl chloride. PVC is available in a number of grades and forms rigid or flexible resins. A flexible resin is obtained by incorporating plasticizers into the resins. 

The authors considered their description of a series of bulk and suspension polymerizations of vinyl chloride with various initiators as very satisfactory [17] with Q St 15. In spite of that, their approach has been criticized by Ugelstad who considers termination of growing radicals exclusively by mutual collisions to be very improbable [19], A large number of primary particles are formed in a short time interval, and many of these are then easily absorbed by the already solid flakes. Desorption of sorbed radicals has also to be considered. Radical distribution among the two phases should be controlled by these processes, especially at low conversion. 

Use Initiator for suspension polymerization of vinyl chloride solution polmyerization of various monomers such as acrylonitrile, MMA, vinyl acetate. 

Material Balance. The next step is the material balance. Here it is necessary to specify the end use of the product. If it is to be electrical, that automatically fixes the catalyst which can be used. The Sales Department s prognostication as to the demand for the product will fix the over-all production. (It is wise for the engineer to get this in writing.) At this point, some laboratory work should be done in order to determine a satisfactory formulation. In this particular case, suspension polymerization of vinyl chloride is rather simple, if the correct formulation is used, so the time consumed need not be great. It will now be possible to settle on a material balance. 

In large jacketed reactors used for suspension polymerization of vinyl chloride, the reaction rate is limited by the rate of heat removal [42,43]. Thick-walled reactors are needed because of the high pressure, and a very smooth surface is desired to minimize fouling. Compare the overall heat transfer coefficients for the following conditions, assuming hi = 300 and hj = 500 Btu/hr ft ... 

Uses Wetting agent, dispersant, emulsifier, penetrant, and solubilizer in emulsion and suspension polymerization of vinyl chloride and styrene for paints, coatings, indirect food additives food-contact paper emulsifier in mfg. of food-contact articles Regulatory FDA 176.180,178.3400 compliances Properties Lt. straw clear llq. sol. in polar and nonpolar soivs. m.w. 584 sp.gr. 1.02 dens. 8.5 Ib/gal cloud pt. -2 C flash pt. (RMCC) 230 F pH 6.0 (10%) surf. tens. 29 dynes/cm (0.1%) anionic 70% act. 

Bis (3,5,5-trimethylhexanoyl) peroxide Di-(2-t-butylperoxyisopropyl) benzene 2,4-Di-t-butylphenyl 3,5-di-t-butyl-4-hydroxybenzoate initiator, suspension polymerization t-Amylperoxy 2-ethylhexanoate initiator, suspension polymerization of vinyl chlorides... 

Industrial suspension polymerizations of vinyl chloride are often carried out in large batch reactors or stirred jacketed autoclaves. Continuous reactors, however, have been introduced in several manufacturing facilities [315]. Typical recipes call for 100 parts of vinyl chloride for 180 parts of water, a suspending agent, like maleic acid-vinyl acetate copolymer, a chain transferring agent, and a monomer soluble initiator. The reaction may be carried out at 100 Ib/in. pressure and 50°C for approximately 15 h. As the monomer is consumed the pressure drops. The reaction is stopped at an... 

Table 3. Typical Primary and Secondary Protective Colloids Used in the Suspension Polymerization of Vinyl Chloride...

Surface Tension in Water (minimum) dynes/cm 28 FDA Approvals 21 CFR Petition Submitted Emulsifier for emulsion and suspension polymerization of vinyl chloride, vinylidene chloride and co-monomers. Reduces... 

The principal characteristics of suspension polymerization have been described in the previous discussion of polystyrene (Section 3.2.3.3). Typically, the suspension polymerization of vinyl chloride is carried out batch-wise in a stirred reactor, jacketed for heating and cooling. The reactor is fitted with a bursting disc (to relieve pressure in case of a runaway reaction) and is also connected to a vacuum line. A typical basic formulation might be as follows ... 

Suspension Polymerization of Vinyl Chloride in Sealed Tubes. 383... 

Suspension Polymerization of Vinyl Chloride with a Mixture of a... 

The kinetic equivalence of bulk and suspension polymerizations of vinyl chloride has been demonstrated [78]. Thus, the suspension polymerization process may be considered as the polymerization of individual monomer droplets in an inert solvent phase. Naturally, some characteristics peculiar to the suspension process may be superimposed on those of the bulk process. This matter has been nicely summarized by Eliassaf [86, 87]. 

Time-lapse photography has been used to follow the course of the suspension polymerization of vinyl chloride. This study showed that the spherical droplets of monomer burst under the action of the shearing force of the agitator to produce deformed and irregular resin particles. Without agitation, on the other hand, opaque spots appear in the spherical monomer droplets that increase in size as the polymerization proceeds [91]. 

While the suspension polymerization of vinyl chloride is the most widely used method industrially, there are a few additional problems that need to be mentioned [97]. 

Table XII gives the half-lives of several initiators which are of interest in suspension polymerizations of vinyl chloride. While these data are a rough guide to the temperature-time relationship to be expected, many other factors need to be considered. For example, lauroyl peroxide brings about a polymerization process of vinyl chloride in which the maximum rate takes place between 60% and 80 o conversion whereas the rate of polymerization with diisopropyl peroxydicarbonate is much more uniform throughout the process. Also, particle structure varies with the initiator used [139]. The development of initiators has been in the direction of molecules with unsymmetrical substitution about the peroxide bridge. Data on these compounds are also included in Table XII [139, 140].

Suspension polymerization of vinyl chloride with preemulsified monomer and interruption of agitation [255]. 

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