Isobutylene polymerizations

Solvent Polarity and Temperature. The dielectric constant and polarizabihty are of Htde predictive value for the selection of solvents relative to polymerization rates and behavior. In spite of the similarity of the dielectric constants of CH2CI2, CH Cl, and C2H C1 these solvents yield quite different isobutylene polymerization rates that decrease in the same order. 

The initiator can be a radical, an acid, or a base. Historically, as we saw in Section 7.10, radical polymerization was the most common method because it can be carried out with practically any vinyl monomer. Acid-catalyzed (cationic) polymerization, by contrast, is effective only with vinyl monomers that contain an electron-donating group (EDG) capable of stabilizing the chain-carrying carbocation intermediate. Thus, isobutylene (2-methyl-propene) polymerizes rapidly under cationic conditions, but ethylene, vinyl chloride, and acrylonitrile do not. Isobutylene polymerization is carried out commercially at -80 °C, using BF3 and a small amount of water to generate BF3OH- H+ catalyst. The product is used in the manufacture of truck and bicycle inner tubes. 

Isobutylene, polymerization of, 1207 Isocyanate. Hofmann rearrangement and,933-934 Isoelectric point (pJ), 1024 calculation of, 1024 table of, 1018-1019 lsoleucine, metabolism of, 911 molecular model of, 304 structure and properties of, 1018 Isomer, conformational, 93 Isomerase, 1041-1042 Isomers, 81... 

Isobutylene Polymerization with Sir-H Containing Initiator Me3Al Initiating System... 

Thus with aMeSt, the kinetic chain is relatively short, monomer is consumed mainly by initiation and propagation, and chain transfer by the HSiCCHj CH H C Q initiator is unfavorable (see Sect. III.B.3.b.i.). In contrast, with isobutylene the kinetic chain may live longer because it is sustained by thermodynamically favorable chain transfer by the initiator. Scheme 5 illustrates the mechanism of isobutylene polymerization by the HSi(CH3)2CH2CH29>CH2Cl/Me3Al system. The kinetic chain is sustained by chain transfer loops shown on the left margin of the Scheme. 

Scheme 5. Mechanism of isobutylene polymerization with the H(CH3) iSiCH2CH2

Effect of Reagent Addition Sequence on Isobutylene Polymerization. 92... 

The first paper of this series concerns the effects of f-BuX, Me3Al, Et2AlX and EtAlCl2, and MeX on PIB yields and polymerization rates. The second paper1 will survey and discuss the effects of reaction variables on molecular weights of PIB and molecular weight control in isobutylene polymerization. 

Although the history of isobutylene polymerization chemistry can be traced back to the nineteenth century12, systematic research began barely forty years ago. The introduction of alkylaluminum coinitiators took place at about the same time13. Since early work has been reviewed by Kennedy and Gillham14, only a comprehensive review of recent study of isobutylene polymerization using alkylaluminum coinitiators will be presented. 

Both chlorine and bromine in conjuction with alkylaluminums were active initiators in isobutylene polymerization. 

V. Isobutylene Polymerization Using f-BuX/Me3 AI Initiator Systems and MeX Solvents... 

It was postulated that the rate decreased as the basicity of the halogen decreased and/or steric compression increased in f-BuX, and as the polarizability of halogen in MeX increased. The objective of the present research was to extend this model study to isobutylene polymerization systems, in particular to investigate the effect of reagent addition sequence and that of the nature of the halogen in f-BuX and MeX on the polymerization rate and PIB yield using Me3 Al coinitiator. 

Table 2. Effect of reagent addition sequence on isobutylene polymerization...

Effect of f-BuX Initiator, MeX Solvent and Temperature on Isobutylene Polymerization... 

In line with the conclusions derived in the model study10), the effect of solvent on initiator reactivity can also be explained on the basis of halogen polarizability in MeX. A detailed discussion of these trends is given in Section VIII. Mel is a poison in isobutylene polymerization. The poisoning activity of Mel will be discussed in Section VII. 

The objective of this phase of investigation was to study the details of isobutylene polymerization using f-BuCl, f-BuBr and f-BuI initiators, Et2 Aid, Et2AlBr and... 

Though Et2 AlBr coinitiator for isobutylene polymerization has been mentioned in the patent literature33, detailed work with this coinitiator has not been reported. Table 5 lists PIB yields and molecular weights obtained using the f-BuX/Et2 AlBr/MeX... 

Since neither r-BuI34 nor I21 s are initiators in conjunction with R3A1 or Et2AlCl, the use of Et2 All becomes important from the point of view of introducing -I in the counteranion. Recently Italian workers23 also used this approach and studied isobutylene polymerization with I2/Et2AU initiator system. 

Isobutylene Polymerization Using H20 /EtAlCl2 Initiator and n-Pentane Solvent... 

Mel poisoning in isobutylene polymerization with r-BuX/Me3Al systems was studied using mixed solvent systems containing various proportions of MeG and Mel. Results, together with experimental details and materials used are reported in Fig. 2. 

This study shows that Mel, and, for some systems, MeBr are potent poisons in isobutylene polymerization. The extent of poisoning increases in the presence of less reactive initiator and by decreasing temperatures. The mechanism of poisoning is discussed in Section VIII. 

---