Isobutylene Polymerisation

Isobutylene (2-methylpropene) is easily polymerised via a cationic mechanism in the presence of electrophilic catalysts to form a wide range of products - from lower oligomers (where the number of links is about 2-3) to polymers with a MW of more than several millions. 

Isobutylene polymerisation, in the presence of metals halides (Lewis acids) combined with Bronsted acids (exemplified by a catalyst based on MeX and H2O), proceeds according to the following scheme  

Reactions of transfer of a proton to a counterion (possible reaction) can be ignored in many cases  

It should be noted that the catalyst regeneration, due to fast reinitiation, is transformed into the reaction of chain transfer to counterion. 

There are several requirements to be met for implementing the zone model in a real process [2] 1) Reaction zones should not cross each other therefore, the distance between adjacent points of catalyst loading should be  

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It is especially interesting to examine the thermodynamics of reaction (i) for the trityl and dityl (diphenylmethyl) cations as initiating salts for isobutylene because we can thus provide a theoretical explanation of the experimental fact that trityl salts do not initiate isobutylene polymerisation, but dityl salts do Table 2 shows the relevant data. The solvation energy terms have been omitted since on the basis of a... 

Isobutylene polymerisation initiated by 1,2-epoxy-2,4,4-trimethylpentane (TMPO-l)/TiCl4 was studied using IR fibre optics. The initiating mechanism involves the formation of tertiary carbocations, by both SNi and SN2 paths. From the linearity of the first-order plots of monomer consumption, and the near uniformity of the polyisobutylene, it was concluded that living polymerisation conditions prevailed (i.e., no termination step) (32). The ATR head can monitor very low concentrations (0.1 mmol/1) (49). 

The initiation rate of isobutylene polymerisation is sufficiently high k, kp) which is why, in process kinetics, the initiation stage is considered to be instant. The concentration of active centres I A corresponds to the catalyst concentration in this case. 

As the main reaction determining the MW and MWD in the isobutylene polymerisation process, over a broad temperature range, is the chain transfer to monomer, then P of a polymer, formed in any section of a sufficiently small reaction volume, is determined by temperature only and does not depend on the catalyst or monomer concentration ... 

According to isobutylene polymerisation kinetics, the following differential equations describe the changing concentration of the monomer and active centres, as well as the temperature distribution in a reaction zone [11] ... 

Simulation of fast isobutylene polymerisation [21] has been carried out on the basis of a mathematical model, which considers the hydrodynamic effects of a reacting mixture during the processes of mixing and chemical transformations. 

Figure 1.1 demonstrates the diffusion model-based fields of temperature, as well as the monomer and catalyst concentrations during the cationic polymerisation of isobutylene. It is clear that the process and experimental behaviour are close, mainly in the catalyst input areas where it is mixed with the monomer solution. Isobutylene polymerisation is similar to the behaviour of fast chemical processes the temperature and reaction rate in a reaction zone depend on the initial concentration of reactants, the value and the factor K, which is the heat transfer through the reactor wall Kjjt. Although the rate of isobutylene polymerisation is maximal within the catalyst input areas, the reaction occurs sufficiently far in the axial direction to result in a change of output characteristics and polymer properties (molecular characteristics) when moving away from catalyst input area. 

Figure 1.1 Fields of temperature, monomer, and catalyst concentrations, formed during the isobutylene polymerisation process. T, K 1 - 310 2 - 313 3 - 320 ...

The study of fast liquid-phase electrophilic isobutylene polymerisation has revealed the influence of reaction zone geometrical parameters (radius R and length L) on... 

Walues in brackets are experimental results, obtained for isobutylene polymerisation in the presence of AICI3 in ethyl chloride (-30 °C (243 K)). The differences observed between the calculated and experimental values of P and can be explained by the contribution of the selected kp/k ratios. Thus, these values are in good agreement. 

Isobutylene polymerisation has been studied to demonstrate that a temperature of 90 °C (liquid ethylene with T, oii = -90 °C (183 K) was used as the cooling agent) allows the polymerisation of about 15 wt% of a liquid, by adiabatic heating of the reaction mixture. There are fewer possibilities for monomer solution cooling when, for example, liquid ammonium is used as a cooling agent (T], , is -30 °C (243 K)), as the reaction mixture heating period will only produce up to 10 wt% of a polymer. 

Thus, we have a closed system of Equations 3.4-3.10 which allow the MWD and average MW to be calculated for a random distribution of polymer yields in each zone (AM,). For determining the relationship between the polymer yield in a separate zone and the amount of catalyst loaded, knowledge of polymerisation kinetic mechanisms is necessary. In particular, using the cationic mechanism of isobutylene polymerisation, the following expressions may be derived [1] ... 

However, the numbering of the cooling zones in the reactor is the cooling zone followed by the reaction zone and has a similar index. In turn, the amount of a polymer obtained in the 2 zone, is related to the amount of catalyst fed in accordance with the kinetic mechanism of the polymerisation reaction. For example, in the case of isobutylene polymerisation, the following relation is true [3] ... 

Figure 5.2 shows the interaction between the input and output parameters of rapid isobutylene polymerisation, occurring in the tubular turbulence reactor, demonstrating the possibility of automated reaction operation. 

Methodological and experimental approaches, along with original results provided below for the model of the fast chemical reaction of liquid-phase electrophilic (cationic) isobutylene polymerisation are general and applicable to other fast liquid-phase processes. They turned out to be fruitful for the description of various chemical processes as well as nonpolymerisation reactions, especially of those with mass exchange (extraction, mixing, dispersion, and so on) as an important factor [27-32],... 

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