Bulk polymerization of vinyl chloride

Perhaps the only process where such correlations have been published is the bulk polymerization of vinyl chloride as reported by Ray, Jain and Salovey (14). 

Finally, similar autoacceleration in the polymerization rate was reported by Crosato-Arnaldi, Gasparini and Talamini (18) for the bulk polymerization of vinyl chloride. 

The literature on the modeling and design of precipitation polymerization reactors is limited primarily to reactor for the bulk polymerization of vinyl chloride (31-38), although other systems have been discussed, particularly in the patent literature (39,40,41). 

It is clear, however, that a simultaneous increase in polymerization rate and molecular weight could either follow from a reduction in the rate of termination or from an increase in the rate of propagation. This last possibility has seldom been considered, except in some of the very early studies such as in the work of BENGOUGH and NORRISH (2J on the bulk polymerization of vinyl chloride where a "catalytic" action was attributed to the precipitated polymer. 

In other words, if any structural formations appear in the liquid, they may become a new reaction medium in which the polymerization may change substantially. The part of such a medium may be played, as we have seen, by fluctuational formations of monomer molecules but there is another possibility. The polymer molecules formed during polymerization are often more unevenly distributed in the monomer than in the solvent. They are much more likely to form structures than monomeric substances. The extreme case is the formation of a polymer which is insoluble in the monomer or in the solvent used for polymerization. In this case the polymer formed is evolved as a new phase, and if polymerization occurs inside or on the surface of the particles of this new phase, structural phenomena will naturally begin to play a major part. Perhaps the most vivid example of such a phenomenon is the bulk polymerization of vinyl chloride, whose structural features were studied recently (6, 7). The peculiarities of this process arise from the fact that... 

The polymer concentration at which autocatalytic effects are significant varies from system to system. When a polymer is insoluble in its own monomer, radicals can be occluded in the precipitated polymer-rich phase where they are prevented from terminating by their low mobilities. Bulk polymerization of vinyl chloride provides an example of this. 

Precipitation polymerization. In precipitation polymerization, monomer is polymerized either in bulk or in solution (aqueous or organic), however, the polymer formed is insoluble in the reaction media. As such, the forming polymer precipitates and the viscosity of the medium does not change appreciably. This pol5mierization is often referred to as powder or granular polymerization because of the forms in which the polymers are produced. Solution polymerization of acrylonitrile in water, and bulk polymerization of vinyl chloride are examples of precipitation polymerization. 

One process for bulk polymerization of vinyl chloride was developed in France, where the initiator and monomer are heated at 60 °C for approximately 12 hours inside a rotating drum... 

One process for bulk polymerization of vinyl chloride was developed in France where the initiator and monomer are heated at 60°C for approximately 12 h inside a rotating drum containing stainless steel balls. Typical initiators for this reaction are benzoyl peroxide or azobisisobutyronitrile. The speed of rotation of the drum controls the particle size of the final product. The process is also carried out in a two-reactor arrangement. In the first one approximately 10% of the monomer is converted. The material is then transferred to the second reactor where the polymerization is continued until it reaches 75-80% conversion. Special ribbon blenders are present in the second reactor. Control of the operation in the second reactor is quite critical [315]. 

For the bulk polymerization of vinyl chloride, the relation between the rate of polymerization, R o, and the conversion, p, is not clearly defined. Some authors state that up top = 3.5< 0, the relation between i po, andp is linear others claim that up to p = 15%, is a function of the frd power of p while still other workers claim that... 

In Table VII, it will be noted that in a bulk polymerization, at a conversion of 10-20%, secondary particles form. That is, swollen polymer particles collide to form larger particles. As the process proceeds, virtually no free liquid monomer is present. Using a special autoclave, in which polymer lumps could be broken up, bulk polymerization of vinyl chloride could be carried out beyond this low conversion range [58]. This concept was improved upon in the basic patent for the Pechiney-Saint Gobain process [59]. Evidently Produits Chimique Pechiney-Saint Gobain was a... 

TABLE VIII Temperature Effect on the Bulk Polymerization of Vinyl Chloride [48]"... 

TABLE IX Bulk Polymerization of Vinyl Chloride in Sealed Glass Tubes... 

In a precipitation polymerization, the system initially is in a homogeneous phase, because monomer and initiator are completely soluble in the initial reaction medium, but, upon initiation, the formed polymer precipitates as soon as it forms. After precipitation, the polymerization proceeds by absorption of monomer and initiator into the polymer particles. Bulk polymerization of vinyl chloride and solution polymerization of acrylonitrile in water are examples of precipitation polymerization. Precipitation polymerizations are often referred to as powder or granular polymerizations because of the forms in which the final polymer products are obtained. 

Mazzolini et al. [251-254] reported the organic hydroperoxide-S02 redox pair and a nucleophilic agent to polymerize vinyl chloride in bulk at subzero temperatures. Patron and Moretti [255] have also reported on the bulk polymerization of vinyl chloride using the same type of system at 20°C... 

According to Mazzolini et al. [251], the kinetic expressions for the continuous bulk polymerization of vinyl chloride by the hydroperoxide-S02 nucleophilic agent may be as follows ... 

During the bulk polymerization of vinyl chloride [251], when cumyl or tert-Bu hydroperoxides and SO2 are used with ethers, ketones, or alcohols, sul-fone groups are incorporated in the polymer chain because of copblymeri-zation of SO2. When the hydroperoxides and SO2 are used with MeO or EtO (from Na or Mg alkoxides), SO2 copolymerization is completely suppressed, provided the Me0 /S02 or EtO /SO2 ratio is at least 1 1. When the feed rate of hydroperoxide is constant, the maximum monomer conversion in continuous bulk polymerization is reached when the SOa/hydroperoxide ratio... 

In two other patents reported by Mazzolini et al. [252,254] for bulk polymerization of vinyl chloride, they used the same type of catalytic system as above. Thus, vinyl chloride was polymerized at — 30°C in the presence of a mixture of cumene hydroperoxide or tert-Bu hydroperoxide, a meth-anolic solution of SO2, and a methanolic solution of NaOMe, NaOEt, or KOMe. 

In another German patent, Mazzolini et al. [253] reported the low-temperature bulk polymerization of vinyl chloride in the presence of a catalyst system consisting of an organic hydroperoxide, SO2, and at least one alkali metal alcoholate at a [R0X]-[S02]/[R 00H] mole ratio of 0-0.5 and 0.005-1% mercapto compound which gave a degree of conversion >18% and a polymer with outstanding physical and chemical properties. The typical recipe for the polymerization is presented in Table 23. 

Patron and Moretti [255] also reported the bulk polymerization of vinyl chloride at >0°C in the presence of a catalyst system consisting of an organic hydroperoxide, SO2, and an alcohol or metal al(X)holate. A 25% conversion was obtained at 25°C. The PVC recovered had an intrinsic viscosity of 1.3 and bulk density of 0.41 g cm . They [260] also reported the bulk polymerization of vinyl chloride by taking a mixture containing liquid vinyl chloride at — 30°C and a catalyst composition containing cumene hydroperoxide, SO2, Na methylate, and 2-mercaptoethanol that was continuously fed to a reactor. The molar weight concentration ratio of the catalyst composition... 

---