Polymerization/workup process

Polychlorotrifluoroethylene (PCTFE) is ordinarily prepared by emulsion polymerization. A polymer suitable for thermal processing requires coagulation, extensive washing, and postpolymerization workup. Coagulation to provide a filterable and washable solid is a slow, difficult process and removal of surfactant is an important part of it. Complete removal may be extremely difficult depending on the extent of adsorption to the polymer particles. Consequently we set out to develop a suspension polymerization process, which would be surfactant-free and afford an easily isolated product requiring a minimum of postreaction workup. 

In this method, attack by an anionic initiator ( -BuLi, potassium alkoxides/cryptand[2.2.2],62 or silyl anions in benzene)63 occurs regioselectively on the less hindered silicon of 9, resulting in an anionically terminated disilanyl-lithium which then attacks another monomer at the less hindered silicon atom. The process continues rapidly (the reaction is usually complete within a few minutes) in a living polymerization fashion to yield 10 on alcohol workup. 

The method for the manufacture of polypropylene by the Ziegler-Natta process, which has been in widespread use for several decades, involved some years ago a polymerization in a relatively volatile solvent, for example a light petroleum fraction. That was the drawback of this process, since in the separation and subsequent drying of the polymer formed the solvent could not be completely recovered. Problems are thus experienced in fulfilling environmental protection requirements. An additional obstacle was the large volume of aqueous waste that is generated during workup of the polymer suspension. 

Polybutadienes are polyfunctional compounds which, in a free-radical environment, are not only graftable to styrene, but also their molecules react with one another, initially with the formation of long-chain branches. On further reaction, a coherent network forms. Crosslinking of the rubber commences even during the polymerization at a conversion of above 50 % and especially increases during workup of the polymer in the finishing zone. This process is time and temperature dependent. 

Phase-transfer catalysts are used to facilitate reactions between reagents that are in two different phases (e.g., 1-bromooctane in toluene with aqueous potassium iodide to form 1-iodooctane). They are usually quaternary ammonium or phosphonium salts or crown ethers. They can complicate the workup of the reaction and may be difficult to recover for reuse. When they are insoluble polymeric ones, workup and recycle can be done by simple filtration.192 The process is called triphase catalysis. In favorable cases, their activity can be comparable with that of their lower molecular weight analogues. They are often based on cross-linked polystyrene, for which spacers between the aromatic ring and the quaternary onium salt can increase activity two- to fourfold. Copolymerization of 4-vinylben-zyl chloride with styrene or N, N- d i m e Ihy I a c ry I a m i d e, followed by treatment with tri-/ -butylphosphine produced catalysts that were used in the reaction of benzyl chloride with solid potassium acetate (5.43).193... 

Predictably, using the iodide 14b (Scheme 4) allowed the reaction to proceed smoothly at 40°C with no polymerization and thus a more facile workup. It is worth noting, however, that the iodide was not commercially available and would have to be prepared from the bromide. Thus, the bromide was selected as our starting material for further processing. 

The anionic polymerization methacrylic acid esters using such classical initiators as bulky RLi requires low temperatures and has other disadvantages. A breakthrough was reported by Webster, et al, at Dupont in 1983. They used 0-silyl ketene ketals as an initiator in combination with nucleophilic catalysts (fluorides) at room temperature. The process also has two other positive features 1) The polymers are living prior to aqueous workup, and 2) The molecular weight distribution is very narrow (D=M /Mn 1.2) ... 

Emulsifier Recovery/Removal from Fluoropolymer Dispersions Fluo-ropolymer dispersions contain all of the fiuorinated emulsifier used during the polymerization step unless a part of it is lost during workup (e.g., up-concentration) and stabilization with nonionic nonfluorinated emulsifiers. In any event, some fiuorinated emulsifier always remains in the dispersion, as all of these steps cannot remove the fiuorinated emulsifier completely, even if they are applied several times, for example, by up-concentration via ultrafiltration with repeated dilution of the up-concentrated dispersion [26]. Although further processing of fluoropolymer dispersions usually destroys the bulk of the fiuorinated emulsifier, it is desirable to recover and reuse the expensive polymerization aid completely while keeping or even improving the quality of the dispersions. 

Overall, the experimental results strongly indicate a clean and effective reaction scheme. The combination of the facile in-situ chain transfer to St-f/H2 during the catalytic polymerization of propylene and the subsequent complete deprotection reaction during the sample workup step affords a very interesting reaction scheme for the preparation of chain-end-functionalized i-PP with a Cl, OH, or NH2 terminal group via a one-pot reaction process. 

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