Catalysts ethylene oxide polymerization

Ethylene oxide polymerization may be initiated similarly by substances (alcohols, amines, mercaptans) capable of generating a hydroxyl group through reaction with the monomer. In the presence of strongly acidic or basic catalysts, successive addition of ethylene oxide molecules proceeds rapidly in the following manner ... 

USE Catalyst in ethylene oxide polymerization in coating fcr spatter-free welding of steel in C02 in oxide cathode. 

Example 2.4 Ethylene oxide polymerizes readily to high conversions under either anionic or cationic conditions. Tetrahydrofuran can be induced to polymerize in the presence of phosphorous or antimony pentafluorides as catalysts. Tetrahydropyran is unreactive under polymerization conditions. Explain these observations. 

In the course of studying products of the CO2 interaction with trivalent rare earth alkoxides, amides, dicyclopentadienylytterbium and stannyl complexes [(Me3SiCH2)3-Sn]3Ln(DME) it has been found that all of them catalyze ethylene oxide polymerization at room temperature [64, 65]. The process results in the CO2 migration from the metallocomplex to the polymer chain. The polymerization of epoxides on other rare earth catalysts has been observed by Shen and coworkers [131]. 

Heterogeneous Catalytic Polymerization. The preparation of polymers of ethylene oxide with molecular weights greater than 100,000 was first reported in 1933. The polymer was produced by placing ethylene oxide in contact with an alkaline-earth oxide for extended periods (61). In the 1950s, the low yield and low polymerization rates of the eady work were improved upon by the use of alkaline-earth carbonates as the catalysts (62). 

Allyl Glycidyl Ether. This ether is used mainly as a raw material for silane coupling agents and epichlorohydrin mbber. Epichlorohydrin mbber is synthesized by polymerizing the epoxy group of epichlorohydrin, ethylene oxide, propylene oxide, and aHyl glycidyl ether, AGE, with an aluminum alkyl catalyst (36). This mbber has high cold-resistance. 

Direct Oxidation of Propylene to Propylene Oxide. Comparison of ethylene (qv) and propylene gas-phase oxidation on supported silver and silver—gold catalysts shows propylene oxide formation to be 17 times slower than ethylene oxide (qv) formation and the CO2 formation in the propylene system to be six times faster, accounting for the lower selectivity to propylene oxide than for ethylene oxide. Increasing gold content in the catalyst results in increasing acrolein selectivity (198). In propylene oxidation a polymer forms on the catalyst surface that is oxidized to CO2 (199—201). Studies of propylene oxide oxidation to CO2 on a silver catalyst showed a rate oscillation, presumably owing to polymerization on the catalyst surface upon subsequent oxidation (202). 

Catalysts. Silver and silver compounds are widely used in research and industry as catalysts for oxidation, reduction, and polymerization reactions. Silver nitrate has been reported as a catalyst for the preparation of propylene oxide (qv) from propylene (qv) (58), and silver acetate has been reported as being a suitable catalyst for the production of ethylene oxide (qv) from ethylene (qv) (59). The solubiUty of silver perchlorate in organic solvents makes it a possible catalyst for polymerization reactions, such as the production of butyl acrylate polymers in dimethylformamide (60) or the polymerization of methacrylamide (61). Similarly, the solubiUty of silver tetrafiuoroborate in organic solvents has enhanced its use in the synthesis of 3-pyrrolines by the cyclization of aHenic amines (62). 

Reaction and Heat-Transfer Solvents. Many industrial production processes use solvents as reaction media. Ethylene and propylene are polymerized in hydrocarbon solvents, which dissolves the gaseous reactant and also removes the heat of reaction. Because the polymer is not soluble in the hydrocarbon solvent, polymer recovery is a simple physical operation. Ethylene oxide production is exothermic and the catalyst-filled reaction tubes are surrounded by hydrocarbon heat-transfer duid. 

Equation 20 is the rate-controlling step. The reaction rate of the hydrophobes decreases in the order primary alcohols > phenols > carboxylic acids (84). With alkylphenols and carboxylates, buildup of polyadducts begins after the starting material has been completely converted to the monoadduct, reflecting the increased acid strengths of these hydrophobes over the alcohols. Polymerization continues until all ethylene oxide has reacted. Beyond formation of the monoadduct, reactivity is essentially independent of chain length. The effectiveness of ethoxylation catalysts increases with base strength. In practice, ratios of 0.005—0.05 1 mol of NaOH, KOH, or NaOCH to alcohol are frequendy used. 

Diehlorotriphenylantimony has been suggested as a flame retardant (177,178) and as a catalyst for the polymerization of ethylene carbonate (179). Dihromotriphenylantimony has been used as a catalyst for the reaction between carbon dioxide and epoxides to form cycHc carbonates (180) and for the oxidation of a-keto alcohols to diketones (181). 

Polymers with much higher average molecular weights, from 90,000 to 4 x 10 , are formed by a process of coordinate anionic polymerization (43—45). The patent Hterature describes numerous organometaUic compounds, aLkaline-earth compounds, and mixtures as polymerization catalysts. Iron oxides that accumulate in ethylene oxide storage vessels also catalyze polymerization. This leads to the formation of nonvolatile residue (NVR) no inhibitor has been found (46). 

An explosive decomposition in an ethylene oxide (EO) distillation column, similar in its results to that described in Section 7.3.2, may have been set off by polymerization of EO in a dead-end spot in the column base where rust, a polymerization catalyst, had accumulated. Such deadends should be avoided. However, it is more likely that a flange leaked the leaking gas ignited and heated an area of the column above the temperature at which spontaneous decomposition occurs. The source of ignition of the leak may have been reaction with the insulation, as described... 

Polyethylene glycol), or Carbowax, is made by anionic polymerization of ethylene oxide using NaOH as catalyst. Propose a mechanism. 

In polymerization by one-component catalysts [chromium oxide catalyst (75), titanium dichloride 159) at ethylene concentrations higher than 1 mole/liter and temperatures below 90°C the transfer with the monomer is a prevailing process. The spontaneous transfer, having a higher activation energy, plays an essential role at higher temperatures and lower concentrations of the monomer. 

The living nature of PCL obtained in the presence of Zn(OAl-(OPri)2)2 has been used to prepare both di- and triblock copolymers of e-caprolactone and lactic acid (42,43). Treatment of the initial living PCL with dilactide afforded a PCL-PLA diblock with M /Mn = 1.12, with each block length determined by the proportions of the reactants, i.e., the ratio of [monomer]/[Zn]. While the living diblock copolymer continued to initiate dilactide polymerization, it failed to initiate e-caprolactone polymerization. To obtain a PCL-PLA-PCL triblock, it was necessary to treat the living PCL-PLA-OAIR2 intermediate with ethylene oxide, then activate the hydroxy-terminated PCL-PLA-(OCH2CH2)nOH with a modified Teyssie catalyst (Fig. 5). 

A porphinatoaluminum alkoxide is reported to be a superior initiator of c-caprolactone polymerization (44,45). A living polymer with a narrow molecular weight distribution (M /Mjj = 1.08) is ob-tmned under conditions of high conversion, in part because steric hindrance at the catalyst site reduces intra- and intermolecular transesterification. Treatment with alcohols does not quench the catalytic activity although methanol serves as a coinitiator in the presence of the aluminum species. The immortal nature of the system has been demonstrated by preparation of an AB block copolymer with ethylene oxide. The order of reactivity is e-lactone > p-lactone. 

The above considerations stimulated investigations of the polymerization of model systems, namely ethylene oxide in the presence of dialkyldichlorostannanes30). R2SnCl2 has been found to be a very active catalyst for the polymerization of ethylene oxide, the polymerization rate increasing considerably with the length of the alkyl substituent at the tin atom. 

Five-coordinate aluminum alkyls are useful as oxirane-polymerization catalysts. Controlled polymerization of lactones102 and lactides103 has been achieved with Schiff base aluminum alkyl complexes. Ketiminate-based five-coordinate aluminum alkyl (OCMeCHCMeNAr)AlEt2 were found to be active catalyst for the ring-opening polymerization of -caprolactone.88 Salen aluminum alkyls have also been found to be active catalysts for the preparation of ethylene carbonate from sc C02 and ethylene oxide.1 4 Their catalytic activity is markedly enhanced in the presence of a Lewis base or a quaternary salt. 

With ethylene oxide the situation is complicated. Worsfold and Eastham [63] showed that under anhydrous conditions in ethylene dichloride solution boron fluoride reacts slowly with the monomer to form a co-catalyst and that after the induction period during which this occurs the polymerization proceeds smoothly and that the induction period can be eliminated if water, equivalent to the boron fluoride, is added to the system. 

The first reported study of a reaction of wood with an epoxide appears to be that of McMillan (1963). This involved the use of gaseous ethylene oxide (Figure 4.9, R=H) at a temperature of 93 °C and a pressure of 3 atmospheres (0.3 MPa). In some cases, the wood was diffusion pre-treated with trimethylamine vapour as the catalyst. A 65 % ASE at 20 % WPG was obtained, attributed to a bulking effect due to in situ polymerization of the epoxide. There was no effect on the static bending strength of samples, and the modified wood became distinctly brown at higher levels of treatment. 

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