Chlorination of polyisobutene

Radiation-induced chlorination of polyisobutene in carbon tetrachloride was studied at various temperatures. The process is a chain reaction with a G value of about 10 to 105, depending on the reaction conditions. At very low dose rates (0.1 to 0.2 rad I sec), the chlorination rate is directly proportional to the dose rate. At higher dose rates, the rate approaches a square-root dependence on the dose rate. The termination reaction and the influence of oxygen are discussed. The reaction is first order with respect to chlorine concentration. An activitation energy of about 4 kcal/mole was obtained. In connection with the chlorination reaction, degradation of the polyisobutene takes place. This degradation was followed by osmometric measurements. The structure of the chlorinated product was briefly investigated by IR spectroscopy. 

Degradation of the polyisobutene chain takes place parallel to the chlorination. This is shown in Figure 5, where the molecular weight Mn is plotted vs. the absorbed radiation dose. A similar effect was observed by McNeill and McGuchan (4) for the thermal chlorination of polyisobutene, which they explained by reaction of a polymer radical formed in the chlorination process ... 

During maintenance work, simultaneous release of chlorine and acetylene from two plants into a common vent line leading to a flare caused an explosion in the line [10]. The violent interaction of liquid chlorine injected into ethane at 80°C/10 bar becomes very violent if ethylene is also present [11]. The relationship between critical pressure and composition for self-ignition of chlorine—propane mixtures at 300°C was studied, and the tendency is minimal for 60 40 mixtures. Combustion is explosive under some conditions [12]. Precautions to prevent explosions during chlorination of solid paraffin hydrocarbons are detailed [13]. In the continuous chlorination of polyisobutene at below 100°C in absence of air, changes in conditions (increase in chlorine flow, decrease in polymer feed) leading to over-chlorination caused an exotherm to 130°C and ignition [14],... 

McNiell has developed a useful technique for the determination of unsaturation using chlorine-36. It is not suggested that the technique should replace existing methods but that it is highly suitable for micro analyses when only small samples are available or for estimation of very low unsaturation values where other methods are not sufficiently sensitive. The superiority of the method for the analysis of butyl rubbers has been demonstrated (61) and it has also been used to measure unsaturation of 0.1—0.01 mole-% of polyisobutene (62). 

The time-conversion curves do not pass through the origin in spite of all precautions taken, there was always a small dark reaction. This dark reaction is obviously caused by traces of light penetrating into the ampule during the preparation and is not caused by a thermal reaction. The conversion of the dark reaction in experimental times is always so small that it does not have any implications for the size of the radiation-induced reaction. Irradiation of a solution of polyisobutene in carbon tetrachloride in the absence of chlorine showed that only negligible amounts of chlorine (about 2 weight %) were taken up from the solvent. 

Harrison [4] prepared poly(isobutylene-g-succinic anhydride) by reacting a 1 1 mole ratio of polyisobutene/maleic anhydride using di-t-butylperoxide as catalyst where the ratio of di-t-butylperoxide/polyisobutene was 0.05 1, respectively. In this procedure polyisobutylene had a Mn of roughly 2300 daltons while the product had a SAP number of 26.2 mg for the KOH/g sample. Poly (isobutylene-g-succinic anhydride) has also been prepared in the simultaneous chlorination/maleation process described by Barini [5]. 

Before the development of living cationic polymerization in the 1980s, Kennedy and his co-workers devised another way to synthesize end-functionalized polymers, which uses special reagents called inifer, or initiator-chain transfer agents [129]. The method is primarily for the synthesis of polyisobutene with a tertiary chlorine terminal, which is, however, a synthon for a variety of other functional groups. These developments have been reviewed extensively [1,3,130] and fall outside the scope of this chapter. 

The reaction mixtures were clear and colourless at temperatures below about -15° the polymer came out of solution during the reaction. The half-lives of the reactions ranged from 2 to 60 s, the yield, rate, and DP were uninfluenced by the sequence in which the catalyst phial and water phial were broken, the DP of the polyisobutenes ranged from 20 to 2 x 105, and elementary and spectroscopic analyses showed the polymers to contain chlorine, OH-groups and vinyl and tri-substituted double bonds. 

To get a better insight into the chlorination reaction, we wanted to avoid a heterogeneous process. Instead of polyethylene or polypropylene, we used polyisobutene, which is soluble in carbon tetrachloride, as are its chlorination products. In addition, we were interested in the structure and properties of the chlorinated products, especially in comparison with polyvinyl chloride (PVC) and vinyl chloride/isobutene (VC/IB) copolymers. 

Figure 5. Plot of Mn of the chlorinated polyisobutene vs. absorbed radiation dose [PIB]=3.5 g/l ...

The structure of the chlorinated products obtained is not yet clear. McNeill and McGuchan concluded from NMR data that, in the thermal chlorination process, both methyl and methylene groups were chlorinated but that the methylene groups were more readily substituted and that even some disubstitution of the methylene groups occurred. We studied our products by infrared-spectroscopy Figure 6 shows the spectra of four chlorinated polyisobutenes with increasing chlorine content. 

The introduction of conjugated diene functions in polyisobutene chains has been recently acconq>lished throu an indirect approach which utilizes the dehydro-haiogenation of chlorinated butyl rubber, i. e. randomly chlorinated poly(isobutene-co-isoprene), by means of basic agents ... 

More recently, the dehydrohalogenation of chlorinated butyl rubber, i. e. iso-butene-isoprene copolymer containing 1.4—1.6 wt % of chlorine, essentially in allylic positions7, was performed successfully8 thus polyisobutene chains carrying random groups of two conjugated double bonds were obtained. 

Unvulcanized butyl rubber resembles polyisobutene of comparable molecular weight in many properties. It is soluble in hydrocarbons and chlorinated hydrocarbons and shows considerable cold flow. 

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