Polymerization of isobutylene

It is intended to study the polymerization reaction of isobutylene. This reaction is known as one of the most important processes for cationic polymerization, and also called catalytic reaction Friedel-Crafts. The high reactivity of the polyisobutene is obtaining a product with high concentration of double bonds. 

The aim of this example is to determine a mode of production of polybutene to obtain a product similar to standard UV-10. This means, to produce a material with a greater concentration of terminal double bonds from the process variables and a commercial catalyst. 

The variables investigated during the process were the temperature and the concentration of co-catalyst (HCl/Cat = 3 and HCl/Cat = 1). The products were characterized by infrared (FT-IR). The infrared analyzes were conducted at room temperature in a Perkin-Elmer 2000 FT-IR at a resolution of 4 cm T 

One of the conditions used for polymerization reactions is described in Table 25.1. The pure isobutene and its mixture with RAFl (from the polybutene) were used as initial reactants in the process. The addition of reagent is conducted slowly, avoiding a significant increase in temperature. After the end of the addition of isobutylene, the temperature remained stable at around 7°C. In an initial volume (reactant + ethanol in dichloromethane) of 1000 mL, a yield of 600 mL was obtained, approximately. 

Volumetric ratio ethanol/dichloromethane Molar ratio BF3/ethanol 

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Derivatives of polyisobutylene (6. in Figure 9.1) offer the advantage of control over the molecular weight of the polyisobutylene obtained by cationic polymerization of isobutylene. Condensation on maleic anhydride can be done directly either by thermal activation ( ene-synthesis reaction) (2.1), or by chlorinated polyisobutylene intermediates (2.2). The condensation of the PIBSA on polyethylene polyamines leads to succinimides. Note that one can obtain mono- or disuccinimides. The mono-succinimides are used as... 

The mechanism of initiation in cationic polymerization using Friedel-Crafts acids appeared to be clarified by the discovery that most Friedel-Crafts acids, particularly haUdes of boron, titanium, and tin, require an additional cation source to initiate polymerization. Evidence has been accumulating, however, that in many systems Friedel-Crafts acids alone are able to initiate cationic polymerization. The polymerization of isobutylene for instance can be initiated, reportedly even in the absence of an added initiator, by AlBr or AlCl (19), TiCl ( )- Three fundamentally different... 

Butyl and Halobutyl Rubber. Butyl mbber is made by the polymerization of isobutylene a small amount of isoprene is added to provide sites for curing. It is designated HR because of these monomers. Halogenation of butyl mbber with bromine or chlorine increases the reaction rate for vulcanization and laminates or blends of halobutyl are feasible for production of mbber goods. It is estimated that of the - 100 million kg of butyl (UR) and halobutyl (HIIR) mbber in North America, over 90% is used in tire apphcations. The halogenated polymer is used in the innerliner of tubeless tires. Butyl mbber is used to make innertubes and curing bladders. The two major suppHers of butyl and halobutyl polymers in North America are Exxon and Bayer (see ELASTOLffiRS,SYNTHETIC-BUTYLrubber). 

Table 2. Polymerization of isobutylene using the (CH3)3CCl/Et2AlCl initiating system in the presence of

Table 10. The effect of solvent polarity on the polymerization of isobutylene by the HSi(CH3)2CH2CH29 CH2Q/Me3Al initiating system...

Production of TPA is much more complex than that of napalm, limiting it to those nations with an advanced petrochemical industry. Because of the reactivity with air, production is usually carried out in an inert atm of nitrogen or helium. Polymerization of isobutylene is also a complex process, requiring catalysts such as Al, Ti or Mo... 

Marek and co-workers 6 studied the polymerization of isobutylene using EtAlCl2 and n-heptane. They found ... 

Living polymerization of isobutylene (IB) by di- and trifunctional initiators to make the nearly uniform rubber mid-block... 

It is much more likely that initiation involves transfer of a proton, or possibly some other cation, to the monomer. Thus, the mechanism proposed by Evans and Polanyi and others to account for the polymerization of isobutylene in the presence of boron trifluoride monohydrate is represented as follows ... 

Rates of polymerization of isobutylene in n-hexane by TiCfi with either water or trichloracetic acid as co-catalyst at —90 to 0°C have been estimated by Plesch from the adiabatic temperature rise. His... 

Dibenzothiophene derivatives have been used as co-catalysts in the addition polymerization of vinyl and diene monomers. Dibenzothiophene itself, in conjunction with vanadium oxychloride, is effective in initiating the polymerization of isobutylene, - although when incorporated in a Ziegler catalyst system, competition between donor and monomer for the most electrophilic sites results in deactivation of the catalyst. Despite the fact that 2-vinyl- - - and 4-vinyldibenzothiophene - readily undergo thermal polymerization,... 

Ionic polymerization may also occur with cationic initiations such as protonic acids like HF and H2SO4 or Lewis acids like BF3, AICI3, and SnC. The polymerization of isobutylene is a common example, shown in Fig. 14.5. Note that the two inductively donating methyl groups stabilize the carbocation intermediate. Chain termination, if it does occur, usually proceeds by loss of a proton to form a terminal double bond. This regenerates the catalyst. 

Which of the following could be used to initiate the polymerization of isobutylene (a) sulfuric acid, (b) boron trifluoride etherate, (c) water, or (d) butyllithium ... 

Sulfuric acid finds commercial application in the polymerization of isobutylene to diisobutylene (a mixture of the two 2,4,4-trimethylpen-tenes) and the copolymerization of isobutylene with the n-butylenes to obtain a more complex mixture of octylenes. Dilute (65-70 %) acid is used at 20-35° for the polymerization of only the isobutylene. The copolymerization occurs in the so-called hot acid polymerization process in which the dilute sulfuric acid is employed at about 80-90°. If more concentrated sulfuric acid is used, particularly acid of concentration above about 90%, conjunct polymerization occurs even at —35°. 

Aluminum chloride, boron fluoride and certain other Friedel-Crafts catalysts catalyze the polymerization of isobutylene, at temperatures below about —70° recent work has indicated that the presence of a promoter such as water is usually necessary (see Section V). A rubberlike polymer is obtained. 

The thermal polymerization of isobutylene (at 370-460° and 540-5350 p.s.i.) is of particular interest because it yields 1,1,3-trimethyl-cyclopentane rather than 2,4,4-trimethyl-l- and -2-pentene (McKinley et al., 11). This cyclic dimer amounted to as much as 45.9% of the total liquid product when the reaction was carried out at 400° and 540 p.s.i. It was suggested that its formation might involve one of three mechanisms ... 

Polymerization of isobutylene, for example, may be explained in terms of this hydrogen switch mechanism by assuming that the hydrogen switch occurs between two molecules of the olefin ... 

The reaction of isobutylene with 91% sulfuric acid at 0° yielded a product which contained 63% of paraffin in the fraction boiling below 200° when 87% sulfuric acid was used only traces of paraffins were found in the corresponding fraction, while with 77 % acid no paraffins at all were produced. No polymerization of isobutylene occurred with 67% acid at 0° at 35°, on the other hand, polymer composed of di- and triisobutylene was obtained. 

The low temperature polymerization of isobutylene (that is, polymerization at temperatures below about —70°) in the presence of Friedel-Crafts catalysts (particularly boron fluoride, aluminum chloride, and titanium tetrachloride, has been studied quite intensely. The reaction is commercially important because it yields a high molecular weight... 

Unlike boron fluoride, titanium tetrachloride does not catalyze the liquid phase polymerization of isobutylene under anhydrous conditions (Plesch et al., 83). The addition of titanium tetrachloride to a solution of the olefin in hexane at —80° failed to cause any reaction. Instantaneous polymerization occurred when moist air was added. Oxygen, nitrogen, carbon dioxide, and hydrogen chloride had no promoting effect. Ammonia and sulfur dioxide combined with the catalyst if these were added in small quantity only, subsequent addition of moist air permitted the polymerization to occur. Ethyl alcohol and ethyl ether, on the other hand, prevented the polymerization even on subsequent addition of moist air. They may be regarded as true poisons. 

The addition of boron fluoride to a nonreacting mixture of isobutylene and titanium tetrachloride at -80° resulted in a rapid polymerization of isobutylene. In other words, as has already been mentioned, the liquid phase polymerization of isobutylene with boron fluoride catalyst apparently does not require the presence of water. 

Water has also been shown to be essential for the liquid phase polymerization of isobutylene with stannic chloride as catalyst (Norrish and Russell, 87). The rates of reaction were measured by a dilatometric method using ethyl chloride as common solvent at —78.5°. With a mixture consisting of 1.15% stannic chloride, 20 % isobutylene, and 78.8% ethyl chloride, the rate of polymerization was directly proportional to the amount of added water (up to 0.43% of which was added). A rapid increase in the rate of polymerization occurred as the stannic chloride concentration was increased from 0.1 to 1.25% with higher concentrations the rate increased only gradually. It was concluded that a soluble hydrate is formed and functions as the active catalyst. The minimum concentration of stannic chloride below which no polymerization occurred was somewhat less than half the percentage of added water. When the concentration of the metal chloride was less than about one-fifth that of the added water, a light solid precipitated formation of this insoluble hydrate which had no catalytic activity probably explains the minimum catalyst concentration. The addition of 0.3% each of ethyl alcohol, butyl alcohol, diethyl ether, or acetone in the presence of 0.18% water reduced the rate to less than one-fifth of its normal value. On the other hand, no polymerization occurred on the addition of 0.3 % of these substances in the absence of added water. The water-promoted reaction was halved when 1- and 2-butene were present in concentrations of 2 and 6%, respectively. 

That the liquid phase polymerization of isobutylene in the presence of aluminum chloride or boron fluoride occurs even in the absence of a third component may be seen in the results of another worker (Houtman, 88). With solid aluminum chloride polymerization occurred at room temperature when isobutylene vapors were passed over the catalyst and at —80° when the isobutylene was in the liquid state. In both cases the reaction was incomplete probably because the catalyst was covered with a layer of polymer. The reaction at — 80° was not however as explosive in character as when moisture was present. When boron fluoride was added to isobutylene at about —80°, the polymerization started immediately in the gas phase above the liquid (owing to a somewhat higher temperature) and sometimes continued for a considerable time before reaction was noticeable in the liquid phase. There was no difference in behavior between the experiments in which the catalyst was led through or over the liquid. It was pointed out, however, that these results are not necessarily in contradiction with those of Polanyi and Evans and co-workers and that it is possible that the presence of moisture is neces-... 

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