Base-catalyzed polymerization

Acrolein produced in the United States is stabilized against free-radical polymerization by 1000—2500 ppm of hydroquinone and is protected somewhat against base-catalyzed polymerization by about 100 ppm of acetic acid. To ensure stabiUty, the pH of a 10% v/v solution of acrolein in water should be below 6. 

Since the principal hazard of contamination of acrolein is base-catalyzed polymerization, a "buffer" solution to shortstop such a polymerization is often employed for emergency addition to a reacting tank. A typical composition of this solution is 78% acetic acid, 15% water, and 7% hydroquinone. The acetic acid is the primary active ingredient. Water is added to depress the freezing point and to increase the solubiUty of hydroquinone. Hydroquinone (HQ) prevents free-radical polymerization. Such polymerization is not expected to be a safety hazard, but there is no reason to exclude HQ from the formulation. Sodium acetate may be included as well to stop polymerization by very strong acids. There is, however, a temperature rise when it is added to acrolein due to catalysis of the acetic acid-acrolein addition reaction. 

The coammonolysis of CH3SiHCl2 and CH3(Un)SiCl2 in the indicated ratios was carried out by the procedure as described for the ammonolysis of CH3SiHCl2 [8]. A mixture of cyclic oligomeric silazanes is to be expected in these reactions, [(CH3(H)SiNH)x(CH3(Un)SiNH)y]n, with more than one ring size present. In each preparation, the soluble, liquid products were isolated and used in the base-catalyzed polymerizations. When a ratio CH3SiHCl2/CH3(Un)SiCl2 of x l (x>l) was used in the ammonolysis reaction, the CH3(H)Si/CH3(Un)Si ratio in the soluble ammonolysis product usually was somewhat less than x l. 

The /3-lactone dimer of dimethylketene can be prepared by pyrolysis of its polyester, which is formed by the base-catalyzed polymerization of dimethylketene.3"6 In addition to the rearrangement of the normal dimer described above,6 the direct dimerization of dimethylketene in the presence of aluminum chloride3 or trialkyl phosphites7 leads to the /3-lactone dimer. 

Another advantage of this method is that no catalyst is needed for the addition reaction this means that the base-catalyzed polymerization of the electrophilic olefin (i.e., a,j8-unsaturated ketones, esters, etc.) is not normally a factor to contend with, as it is in the usual base-catalyzed reactions of the Michael typCi It also means that the carbonyl compound is not subject to aldol condensation which often is the predominant reaction in base-catalyzed reactions. An unsaturated aldehyde can be used only in a Michael addition reaction when the enamine method is employed. 

A few polymerizations leading to nonhydrolyzable polysaccharides have been reported. The first was a base-catalyzed polymerization of 5,6-anhydro-l,2-0-isopropylidene-3-0-methyl-a-D-glucofuranose.u The polymerization was initiated most successfully with solid potassium or cesium hydroxide, and the d.p. achieved was —25. Hydrolysis gave a free, methylated, nonhydrolyzable polysaccharide, which was oxidized with hypoiodite to the poly(D-gluconic acid.)... 

Polyether Polyols. Polyether polyols are addition products derived from cyclic ethers (Table 1). The alky lens oxide polymerization is usually initiated by alkali hydroxides, especially potassium hydroxide. In the base-catalyzed polymerization of propylene oxide, some rearrangement occurs to give allyl alcohol. 

Electroluminescence (EL) spectra of P-l-P-4 are given in Fig. 6 [29,30]. The EL spectra of the polymers were obtained for the light-emitting diodes (LEDs) fabricated between the indium-tin oxide (ITO) coated glass anode and the aluminum cathode. For P-l-P-3, their organic soluble precursor polymers were coated onto the ITO-coated glass and they were subjected to thermolysis at 270 °C for 12 h to convert them into the final polymers. And then aluminum cathode was vacuum deposited on the polymer films. P-4 obtained by base-catalyzed polymerization of the bis-bromomethyl monomer was organic soluble and, thus,... 

Polyether Polyols. Polyether polyols are addition products derived from cyclic ethers (Table 4). The alkylene oxide polymerization is usually initiated by alkali hydroxides, especially potassium hydroxide. In the base-catalyzed polymerization of propylene oxide, some rearrangement occurs to give allyl alcohol. Further reaction of allyl alcohol with propylene oxide produces a monofunctional alcohol. Therefore, polyether polyols derived from propylene oxide are not truly difunctional. By using zinc hexacyano cobaltate as catalyst, a more difunctional polyol is obtained (20). Olin has introduced the difunctional polyether polyols under the trade name POLY-L. Trichlorobutylene oxide-derived polyether polyols are useful as reactive fire retardants. Poly(tetramethylene glycol) (PTMG) is produced in the acid-catalyzed homopolymerization of tetrahydrofuran. Copolymers derived from tetrahydrofiiran and ethylene oxide are also produced. 

Draw a mechanism for a base-catalyzed polymerization of methyl a-methacrylate to give the Plexiglas polymer. 

Methyl a-cyanoacrylate (Super Glue) is easily polymerized, even by weak bases. Draw a mechanism for its base-catalyzed polymerization, and explain why this polymerization goes so quickly and easily. 

Elastomers and nonsilanol terminated fluids are produced by base-catalyzed polymerization of low-molecular weight siloxanes. Polydimethylsiloxanes are also produced by ring opening polymerization of D3, D4, and D5. In the presence of MM or MDDM (endcapper), silicones MD M are formed otherwise, silanol terminated polysiloxanes may be obtained. 

Joyce and Ritter (1) in 1941 obtained a patent on the base catalyzed polymerization of caprolactam. They described the reaction of a small amount of sodium or other alkali metal in caprolactam to form sodium caprolactam and the rapid, exothermic polymerization of caprolactam above 200°C to form molten nylon polymer. The polymerization reaction is an isomerization of the low viscosity cyclic amide to a high viscosity, high molecular weight polyamide. 

In 1955, Monsanto Company began exploratory research on the base catalyzed polymerization of lactams. A two-stage mechanism for the thermally-initiated anionic polymerization was postulated as shown in Figure 1. This proposed mechanism was first published in Italian patent 580069 which was issued July 28, 1958. (2)... 

Polymers of this type are produced by either acid- or base-catalyzed polymerizations of cyclic siloxanes where trisubstituted siloxanes are used to end-cap the polymer chains and control the viscosity (VII). 

Some methyl vinyl ketones behave similarly to acetophenones in aldol condensations, a primary requirement being that the vinyl ketone not be particularly susceptible to Michael addition or base-catalyzed polymerization processes. A recent example utilizes the vinylogous p-keto sulfide (15), which undergoes smooth condensation with benzaldehyde and its derivatives (equation 87). The product of this aldol condensation, enone (16), may be converted by a straightforward sequence of steps into the dienal (17), which is obtained as a 4 1 mixture of ( )- and (Z)-isomers at the C(2>=C(3) double bond. A number of other examples of this useful process are reported in the primary publication. 

Actually, the earliest examples of anionic polymerization studied were the base-catalyzed polymerizations of ethylene oxide involving a ring-opening chain reaction ... 

Anionic, base catalyzed polymerization of propylene oxide and higher epoxides are complicated by the E2 elimination acting as a chain transfer, e.g. 

This reaction limits the maximum degree of polymerization of based catalyzed polymerization at operable temperature of propylene oxide polymerization, the ratio k Jka... 

The subsequent mechanism of the base-catalyzed polymerization of caprolactam is complicated. Ring opening of the initiated monomer does not occur. Since the lactam anion is stabilized by resonance, viz.,... 

Type 2 reactions involve violent base-catalyzed polymerization of reactants causing explosions. A base such as caustic soda may catalyze the polymerizations of many organic unsaturates. Violent explosions occurred when caustic soda was mixed with acrolein, acrylonitrile, or allyl alcohol (NFPA 1986). 

Similar to caustic soda, caustic potash can initiate base-catalyzed polymerizations of acrolein, acrylonitrile, allyl alcohol, and other organic unsaturates susceptible to polymerization, often resulting in explosions. 

The reactivity of aliphatic amines is low. Strongly basic, these compounds react vigorously with concentrated mineral acids. The explosion hazards from amines are very limited. They may promote base-catalyzed polymerization of many unsaturated organics. Such reactions are exothermic and can become violent if not controlled properly. Reactions with perchloric acid, hypochlorites, and chlorine may produce unstable products that may explode. 

Isopropylamine forms explosive mixtures with air in the range 2.0-10.4% by volume in air. Vigorous reactions may occur with strong acids and oxidizers. Contact with acrolein may cause base-catalyzed polymerization, which is highly exothermic. 

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