Molecular weight processing methods

FIFE is made commercially by two major processes, one leading to the so called granular polymer and the second leading to a dispersion of polymer of much finer particle size and lower molecular weight. One method of producing the latter involved the use of a 0.1 % aqueous disuccinic acid peroxide solution. The reactions were carried out at temperatures up to 90°C. It is understood that the Du Pont dispersion polymers, at least, are produced by methods based on the patent containing the above example. 

More extensive surveys of molecular weight determination methods may be found in other volumes [21-23]. Their relevance to mechanochemical processes is summarized below. 

In this method, the plasma state is only used in the initial stage, to initiate the polymerization. The formed active molecules are transferred fi om the plasma phase to the monomer phase (liquid or solid), in which the chain growth reaction runs already without the plasma participation. As a result of this process one gets a conventional polymer, built of mers, which often exhibits a very high molecular weight. This method is particularly useful for the pol5merization of water-soluble monomers such as acrylamide and its derivatives. 

Polyamines can also be made by reaction of ethylene dichloride with amines (18). Products of this type are sometimes formed as by-products in the manufacture of amines. A third type of polyamine is polyethyleneimine [9002-98-6] which can be made by several routes the most frequently used method is the polymeriza tion of azitidine [151 -56 ] (18,26). The process can be adjusted to vary the amount of branching (see Imines, cyclic). Polyamines are considerably lower in molecular weight compared to acrylamide polymers, and therefore their solution viscosities are much lower. They are sold commercially as viscous solutions containing 1—20% polymer, and also any by-product salts from the polymerization reaction. The charge on polyamines depends on the pH of the medium. They can be quaternized to make their charge independent of pH (18). 

Many challenging industrial and military applications utilize polychlorotriduoroethylene [9002-83-9] (PCTFE) where, ia addition to thermal and chemical resistance, other unique properties are requited ia a thermoplastic polymer. Such has been the destiny of the polymer siace PCTFE was initially synthesized and disclosed ia 1937 (1). The synthesis and characterization of this high molecular weight thermoplastic were researched and utilized duting the Manhattan Project (2). The unique comhination of chemical iaertness, radiation resistance, low vapor permeabiUty, electrical iasulation properties, and thermal stabiUty of this polymer filled an urgent need for a thermoplastic material for use ia the gaseous UF diffusion process for the separation of uranium isotopes (see Diffusion separation methods). 

High molecular weight polymers or gums are made from cyclotrisdoxane monomer and base catalyst. In order to achieve a good peroxide-curable gum, vinyl groups are added at 0.1 to 0.6% by copolymerization with methylvinylcyclosiloxanes. Gum polymers have a degree of polymerization (DP) of about 5000 and are useful for manufacture of fluorosiUcone mbber. In order to achieve the gum state, the polymerization must be conducted in a kineticaHy controlled manner because of the rapid depolymerization rate of fluorosiUcone. The expected thermodynamic end point of such a process is the conversion of cyclotrisdoxane to polymer and then rapid reversion of the polymer to cyclotetrasdoxane [429-67 ]. Careful control of the monomer purity, reaction time, reaction temperature, and method for quenching the base catalyst are essential for rehable gum production. 

Molecular Weight. PE mol wt (melt index) is usually controlled by reaction temperature or chain-transfer agents. Reaction temperature is the principal control method in polymerization processes with Phillips catalysts. On the other hand, special chemical agents for chain transfer are requited for... 

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