Stannic chloride cationic polymerization

Homogeneous catalysts are also often used in cationic and anionic polymerization processes. Lewis acid catalysts, such as boron trifluoride and stannic chloride, accept protons from co-... 

Another differential reaction is copolymerization. An equi-molar mixture of styrene and methyl methacrylate gives copolymers of different composition depending on the initiator. The radical chains started by benzoyl peroxide are 51 % polystyrene, the cationic chains from stannic chloride or boron trifluoride etherate are 100% polystyrene, and the anionic chains from sodium or potassium are more than 99 % polymethyl methacrylate.444 The radicals attack either monomer indiscriminately, the carbanions prefer methyl methacrylate and the carbonium ions prefer styrene. As can be seen from the data of Table XIV, the reactivity of a radical varies considerably with its structure, and it is worth considering whether this variability would be enough to make a radical derived from sodium or potassium give 99 % polymethyl methacrylate.446 If so, the alkali metal intitiated polymerization would not need to be a carbanionic chain reaction. However, the polymer initiated by triphenylmethyl sodium is also about 99% polymethyl methacrylate, whereas tert-butyl peroxide and >-chlorobenzoyl peroxide give 49 to 51 % styrene in the initial polymer.445... 

Relatively few attempts have been made to demonstrate the presence of ions in the polymerization of styrene, the most extensively studied of all monomers. Pepper [11] made conductivity studies on stannic chloride solutions in various solvents with and without monomer and added water, using open systems. He concluded that his results shed little light on the question of whether chain-carrying cations were present (which, indeed, he presumed) or on their concentration. Brown and Mathieson [12] found that for the polymerization of styrene by chloroacetic acids in nitromethane, the conductivity was indistinguishable from zero when no water was added, although the reaction rate was appreciable, and with increasing amounts of added water the conductivity increased, but the polymerization rate decreased. Therefore their results gave no useful information on the question of the participation of carbonium ions. 

Injected 6.5 ml (5.90 g or 0.00566 mol) of styrene monomer to the tube containing 30 ml methylene chloride. After this tube has cooled for about 10 min in the ice bath to 0°C, inject with 4 ml of the cool stannic chloride solution (cationic initiator) from the other test tube. Recorded the time it is injected (start of polymerization). 

Cationic mechanisms are much more characteristic of the polymerization of oxygen heterocycles, both ethers and acetals. A wide variety of catalysts has been used, including protonic acids, such Lewis acids as boron trifluoride, phosphorus pentafluoride, stannic chloride, antimony pentachloride, titanium tetrachloride, zinc chloride, and ferric chloride, and salts of carbocations or tri-alkyloxonium ions having anions derived from Lewis acids. Some complex, coordination catalysts that appear to operate by a mechanism... 

A typical cationic polymerization is conducted with highly purified monomer free of moisture and residual alcohol, both of which act as inhibitors, in a suitably dry unreactive solvent such as toluene with a Friedel-Crafls catalyst, e.g., boron trilljoride, aluminum trichloride, and stannic chloride. Usually low temperatures (—40 to — 70 C.) are favored in order to prevent chain-transfer or side reactions. 

The cocatalytic activity of alkyl halides in the cationic polymerization of styrene in the presence of stannic chloride (17), in the polymerization of butadiene with Et2AlCl-cobalt compound (10) and R3Al-cobalt compound (23) catalyst systems and in the cationic polymerization of isobutylene (12) and styrene (13) in the presence of Et2AlCl is well documented. It is reasonable to propose that a reaction between Et2AlCl and a labile chlorine atom on PVC results in the generation of a carbonium ion on the polymer backbone. 

Recently Russian workers claimed that the presence of cocatalysts was not a necessary requirement for cationic polymerization of styrene and isoprene with stannic chloride catalyst provided the temperature and/or the dielectric constant of the medium was high enough (53—55). Similar ideas have also been expressed by Japanese investigators (56). 

Catalyst. Any cationic polymerization catalyst can be used, but jH eferable catalysts are Lewis acid catalysts, such as BFj-etherate and p-toluenesulfonic acid, a combination of it and a Lewis acid also can be used. Inorganic catalysts, such as ferric chloride, stannic chloride, phosphoric pentachloride, and trichloroacetic acid can also be used. The IB-oper amount of the catalyst is in a range of about 0.05 to 2.0 wt % of pyranyl monomers. 

Cationic polymerizations of isoprene proceed more readily than those of butadiene, though both yield low molecular weight liquid polymers. AICI3 and stannic chloride can also be used in chlorinated solvents at temperatures below 0 °C. Without chlorinated solvents, however, polymerizations of isoprene require temperatures above 0 °C. 

Cationic polymerizations of isoprene proceed more readily than those of butadiene, though both yield low molecular weight liquid polymers. AICI3 and stannic chloride can be used in chlorinated solvents at temperatures below 0°C. Without chlorinated solvents, however, polymerizations of isoprene require temperatures above 0°C. At high conversions, cationic polymerizations of isoprene result in formations of some cross-linked material [120]. The soluble portions of the polymers are high in trans-, A structures. Alfin catalysts yield polymers that are higher in trans-l,A structures than free-radical emulsion polymerizations [121]. 

The cationic polymerization of alloocimene, also ocimene and myrcene, has been achieved with metal halide catalysts (e.g., stannic chloride, aluminum chloride, or boron trifluoride) in liquid phase (e.g., ethyl chloride, ethylene dichloride, or benzene) at a temperature range of —35°C to about 200°C. MWs and microstructures of the products were not provided [40]. Cationic (or radical) copolymerizations of alloocimene (or myrcene) with for instance styrene yield resinous copolymers [42]. 

The cationic copolymerization was carried out in air at 25°C in a nitrobenzene solution using stannic bromide as catalyst, while the anionic polymerization was studied in air with sodium dissolved in anunonia [186]. Although many monomers may be polymerized by quaternary ammonium salts, vinyl acetate does not produce any polymer on treatment with dimethylphenylbenzylammonium chloride [187]. 

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