Popcorn polymerization

Proliferous Polymerization. Eady attempts to polymerize VP anionicaHy resulted in proliferous or "popcorn" polymerization (48). This was found to be a special form of free-radical addition polymerization, and not an example of anionic polymerization, as originally thought. VP contains a relatively acidic proton alpha to the pyrroHdinone carbonyl. In the presence of strong base such as sodium hydroxide, VP forms cross-linkers in situ probably by the following mechanism ... 

Popcorn Polymerization CO-Polymerization, frequendy referred to as popcorn polymerization because of the appearance of the product, can be a dangerous side reaction if not carefully controlled. The polymeriza tion appears to proceed without external initia tion (69—71), and is catalyzed by the tightly gelled polymer seeds that are a product of the polymerization. Once seeds are present and immersed either in the Hquid or vapor phase of monomer, their weight increases exponentially with time. 

Popcorn polymerization, 79 835 Popping, coating film defect, 7 123-124 Poppy seed, 23 170 Population balances, 3 120-121 Population inversion, 74 658 Porcelain, 5 582... 

Studies in the grafting of mixed monomers to cellulose have also been reported by Sakurada (113). Binary mixtures studied included butadiene with styrene or with acrylonitrile, and styrene with acrylonitrile. Remarkable increases in rate in the case of mixed monomer similar to those found by RAPSON were found in many cases. For example, about 10% of butadiene increased the grafting yield about ten fold. Similar results were found with the addition of acrylonitrile to butadiene and to styrene. Ternary mixtures of monomers were also investigated by both Rapson (109) and Sakurada (113). The large increases in rate with certain mixtures were interpreted by Sakurada as due to a particular balance of gd effects akin in many ways to popcorn polymerization. The effects were found also with polyvinyl alcohol but not with polyethylene where gel effects would perhaps be less prominent. 

Crospovidone, which is slightly cross-linked with bifunctional monomers (e.g., l-vinyl-3-ethylidenepyrrolidone, ethylene-bis-3-(N-vinyl-pyrrolidone), is obtained by popcorn polymerization. It has been used as a disintegration agent for tablets. 

Acetylene and formaldehyde are reacted in the presence of a highly active catalyst to form butynediol, which is hydrogenated to butanediol and then cyclodehydrogenated to form butyrolactone. Pyrrolidone is produced by reacting butyrolac-tone with ammonia. This is followed by a vinylation reaction in which pyrrolidone and acetylene are reacted under pressure. The monomer vinylpyrrolidone is then polymerized in solution, using a catalyst. Crospovidone is prepared by a popcorn polymerization process. 

Insoluble polyvinylpyrrolidone (crospovidone) is obtained by popcorn polymerization of N-vinylpyrrolidone [2], which yields a mainly physically crosslinked polymer [4-6]. The process is illustrated in Fig. 4 and uses either an alkali hydroxide at temperatures over ioo°C, which yields some bifunctional monomer, or a small percentage of bifunctional monomer in water to initiate crosslinking of the polymer. 

Radical polymerization can be carried out under homogenous as well as heterogenous conditions. This difference is classified based on whether the initial mixture and/or final product are homogenous or heterogenous. Some homogenous mixtures become heterogenous as polymerization proceeds as a result of insolubility of the resulting polymer in the reaction media. There are many other specialized processes that are used to synthesize materials via free-radical polymerization. These include interfacial polymerization, gas phase reactions ( popcorn polymerization ), as well as the use of specialized media like supercritical fluids. Current research efforts include the study of such... 

Ethylene, vinyl acetate, and acrylonitrile are polymerized in this way. The redox initiated polymerization of acrylonitrile is an example of precipitation polymerization where the polyacrylonitrile formed is insoluble in water and separates as a powder. This can lead to undesirable side reactions known as popcorn polymerizations when tough cross-linked nodules of polymer grow rapidly and foul the feed lines in industrial plants. 

Kinetics, degrees of polymerization, and constitution can be changed, however, by a series of other reactions (see Section 20.4). Under certain conditions, for example, the appearance of cauliflower-shaped forms, frequently representing cross-linked polymers, is observed (popcorn polymerization). 

J. W. Breitenbach, Popcorn polymerizations, Adv. Macromol. Chem. 1,139 (1%8) Proliferous... 

During World War I, poly (dimethyl butadiene) was manufactured under the name methyl rubber as a substitute for the natural rubber that the Central Axis Powers lacked. H-type poly(dimethyl butadiene) was obtained by letting the monomer stand for three months in ventilated metal drums. The white, solid crystalline material thus obtained by popcorn polymerization becomes... 

Popcorn polymerization n. Polymerization reaction in which the material s molecular matrix has been penetrated due to vapor pressure by uninhibited monomer. 

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