Isoprene, polymerisation

There has also been some interest in NHC-lanthanide complexes as polymerisation catalysts. Indenyl and fluorenyl functionalised NHC complexes of structures 14 and 15 (Fig. 4.5) were evaluated for isoprene polymerisation following activation... 

In 1954, 1,4-cA-polyisoprene, the synthetic equivalent of natural rubber, was obtained in the laboratories of Goodrich-Gulf [22] by isoprene polymerisation with new catalysts developed by Natta, and later on 1,4-trans-polyisoprene, a synthetic analogue of gutta percha, was obtained by Natta et al. [23]. 

Metal alkyls, preferably of alkali metals such as alkyllithium, exhibit quite good effectiveness in isoprene polymerisation [4-6]. 

Conjugated dienes have been polymerised using supported half-sandwich metallocene catalysts. For instance, catalysts derived by supporting CpTiCl3 on alumina-silica gels, containing—0-Ti(Cp)Cl2 species, displayed activity in isoprene polymerisation without the addition of any other activator. Depending on the alumina-silica gel composition, the kind of polymerisation medium and the temperature, these catalysts exhibited various activities and selectivities polyisoprenes with a predominant 3,4 structure and mixed 1,2/ trans-1,4 structure were obtained [118,119],... 

Figure 3.10 Dependence of the relative difference isOilotiax between TiCl4-Al(f-C4H9)3 catalyst volume fractions (isoprene polymerisation), in axial and peripheral zones of a tubular turbulent prereactor, on the particle diameter d and reaction mixture linear flow rate Vf. = 867 kg/m, p2 = 2670 kg/m, and //j = 0.552 mPa-s...

The study of the influence of turbulent mixing on the modification of microheterogeneous Ziegler-Natta systems has been carried out in an experimental pulse-mode device (Figure 3.11), with a varied method of catalyst preparation. Isoprene polymerisation conversion curves have been obtained by gravimetric method. 

Method 4 The solutions of preliminary prepared and matured catalytic complex and monomer in tanks 1 and 2 respectively, are mixed in device 3, and a reaction mixture is subsequently fed into device 4 (reaction mixture formation in a turbulent mode). Traditional conditions for isoprene polymerisation are provided in the volume device (flask) 4 with slow mixing by a magnetic stirrer (100 rpm). Tubular turbulent device 3 is a prereactor (Figure 3.11). 

Figure 3.11 An experimental device for isoprene polymerisation. 1 and 2) tanks for reactors 3) tubular turbulent device 4) vessel 500 sm 5) three-way tap and 6)...

Figure 3.14 Isoprene polymerisation in the presence of TiCl4-Al(f-C4H9)3 catalyst (1-3) and TiCl4-Al(f-C4H9)3-piperylene (4-6). Hydrodynamic impact on a catalytic system, in a turbulent mode (2, 5), catalyst formation (3) and reaction mixture (6) traditional method (1, 4). The concentration of titanium Ct, - 6 mmol/1, = 1.5 mol/1, Ti/Al/piperylene = 1/1.02/2, the catalyst is matured for...

Experimental results demonstrate that an increase of the specific surface of the catalyst, in processes of stereospecific diene polymerisation (for example, isoprene polymerisation), is a good albeit, insufficient way to increase the process rate. A catalytic system obtains substantial activity when the catalyst and monomer solutions are mixed in a turbulent mode (Method 4) (Figure 3.14, Curve 6). In this case, there is the grinding process of catalyst particles (Figure 3.12, Curve 4) by the hydrodynamic impact, as well as its uniform distribution in a reaction mixture. In addition, the effect can be more substantial due to a decrease of the diffusion limitations for the addition of the first monomer molecule to the AC (fast initiation). A high polyisoprene ( 80%) yield is, in this case, reached in around 20 min. 

Table 3.7 Isoprene polymerisation by TiCl4-Al(t-C4H9)3 catalyst, kp is the chain growth reaction rate constant is the concentration of AC k, are chain-to-monomer and chain-to-aluminium-organic compound transfer reaction rate constants respectively, w is the initial polymerisation rate, method 1) traditional, 2) hydrodynamic impact on a separately prepared catalytic system, 3) catalytic system formation in a turbulent mode, and 4) preliminary formation of a reaction mixture in a turbulent mode...

Similar change in the rate of stereospecific isoprene polymerisation by microheterogeneons Ziegler-Natta catalysts can also be observed for polyisoprene synthesis with a V-Al catalytic system (Figure 3.15). 

Figure 3.15 Isoprene polymerisation in the presence of VOCl3-Al(f-C4H9)3 (1-4) and VOCl3-Al(/-C4H9)3-piperylene (5-8). Traditional process method (1, 5), catalytic system formation (3, 7) reactive mixture (4, 8) and hydrodynamic impact on catalyst particles (2, 6) in the turbulent mode. V/Al/piperylene = 1/2.4/5, Cy = 6 mmol/1, = 1.5 mol/1, the catalyst is matured for 35 min at 0 °C...

Therefore, the opportunity of preparing heterogeneous catalysts on the basis of TiC -A1(/-C4H9)3 and VOCl3-Al(f-C4H9)3, in a tubular diffuser-confusor prereactor operating in the turbulent mode, is a flexible way to control the isoprene polymerisation rate and reduce the catalyst consumption. 

Figure 3.17 The dependence of on isoprene polymerisation time in the presence of TiCl4-Al(i-C4H9)3 (1, 3) and TiCl4-Al(i-C4H9)3-piperylene (2, 4) catalytic systems. The traditional method (1, 2) and hydrodynamic impact on a catalytic system in the turbulent mode (3,4)...

Changing the isoprene polymerisation method, in the presence of a titanium catalyst, exerts a different influence on the width of the MWD. The hydrodynamic impact on the double Ti-Al catalytic system, in the turbulent mode, results in the formation of... 

Figure 3.20 Dependence of the M /M during isoprene polymerisation in the presence of TiCl4-Al(f-C4H9)3-piperylene catalyst. 1 - the traditional method (Method 1) and 2 - catalytic system formation in turbulent streams...

Formation of the TiCl4-Al(/-C4H9)3 catalyst in the turbulent mode (excluding Method 3) does not change the polyisoprene microstructure (Table 3.8). A highly stereoregular polymer is formed in all cases. Isoprene polymerisation in the tubular turbulent prereactor, in the presence of the Ti-Al catalyst, leads to the formation of the polymer with an increased content of a s-l,4-links, (up to 96.8%) and a lower content of 1, -trans and 3,4-links (1.7% and 1.5%, respectively). 

Another mathematical model has been proposed for isoprene polymerisation kinetics. This model takes into consideration the nonuniformity of the AC [85]. It also provides tools for calculation of the monomer conversion time and the average MW of the polyisoprene for various concentrations of reactants, reaction times, and probability of various processes. The estimation of model kinetic parameters using experimental data is also provided. 

Figure 3.31 Kinetic activity distribution of the NdCl3 3TBF-Al(2-C4H9)3 catalytic system in the isoprene polymerisation reaction conversions % 1 - 2.6 2 - 6.4 ...

Figures 3.33 and 3.34 demonstrate the kinetic activity distribution functions obtained from monomodal MWD curves for PrCl3-3(tributylphosphate)-Al(i-C4H9)3 and GdHal3-3(tributylphosphate)-Al(i-C4H9)3 catalytic systems in the isoprene polymerisation process. The functions demonstrated in the fignres are also seen to be polymodal. The initial stage of isoprene polymerisation demonstrates that the activity of AC, formed by both neodyminm and praseodymium catalytic systems, is predominant in the maximum of the low molecular weight area of the /(/w P)-ln M distribution curves (Figure 3.32).

Figure 3.33 PrCl3 3TBF-Al(/-C4H9)3 catalytic system kinetic activity distribution curves in the process of isoprene polymerisation. Isoprene conversion % 1 - 1.9 2 - 2.4 3 - 3.1 4 - 3.6 5 - 19.7 and 6 - 89.6...

Figure 3.35 Kinetic activities of various types of AC in isoprene polymerisation with the LnCl3-3(tributylphosphate)- A1(/-C4H9)3 catalytic system at different monomer conversion rates. Polymerisation conditions tolnene, = 1.5, C i = 4.5 X 10 mol/1, = 25 °C, and Al/Ln = 30. Ln Nd (1), Gd (2) and Pr...

The study of Ti-Al catalytic systems used for isoprene polymerisation revealed three types of AC responsible for the formation of a polymer fraction with a specific MW Type l-lnM = 6.1-9.8 Type H-lnM= 10.5-11.8 and Type IH - / M = 12.3-15.0 (Figure 3.40). The hydrodynamic impact on the Ti-Al catalytic systems, in the turbulent mode, leads to the redistribution of the macromolecule growth centres between various types of AC and a higher activity is demonstrated by the centres responsible for the high MW polyisoprene fraction. 

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