Piperylene polymerisation

The objective of this chapter is to examine the basic research on diene (butadiene, isoprene, and piperylene) polymerisation with the LnHalj-nL-AlRj (Ln = lanthanide, Hal = halogen, ligand (L) = tributyl phosphate (TBP), AlRj = triisobutylaluminum and diisobutylaluminum hydride) catalytic system. The chapter will analyse the role of such factors as the electronic and geometric structure of bimetallic active centres, anti-syn and 7t-o-transitions of the terminal units of the growing polymer chains and the nature of the lanthanide, diene, and organoaluminum component in the mechanism of stereoregulation. 

Figure 3.2 Appearance of steric hindrances by piperylene polymerisation (a, b) and by...

The use of different catalytic systems of both ionic [10] and ionic-coordination [13, 14] types in piperylene polymerisation has been proposed. Because of a high reaction rate of chain transfer to monomer (which grows as catalyst acidity increases) and to solvent (which drops as solvent polarity increases) in cationic polymerisation, a polymer with low MW is obtained. Some halides of metals of groups III-V were tested as catalysts of cationic piperylene polymerisation the most suitable were TiCl4 and SnC. The application of SbCl5 and InClj does not ensure an acceptable polymerisation rate and in the case of using AICI3, the insoluble polymer is obtained. 

Electrophilic (cationic) piperylene polymerisation may be schematised as follows ... 

The elementary steps of the cationic piperylene polymerisation process are similar to those for isobutylene. 

The abovementioned materials can be mixed with one another. A series of other polymers and resins can also be added if the substances listed in 1 to 4 form the bulk of the material. Additional materials are PE, PP, low molecular weight polyolefins, polyterpenes (mixtures of aliphatic and cycloaliphatic hydrocarbons produced by polymerisation of terpene hydrocarbons), polyisobutylene, butyl rubber, dammar gum, glycerine and pentaerythritol esters of rosin acid and their hydration products, polyolefin resins, hydrated polycyclopentadiene resin (substance mixtures manufactured by thermal polymerization of a mixture mainly composed of di-cyclopentadiene with methylcyclopentadiene, isoprene and piperylene which is then hydrogenated). 

The assumption about the bimetallic bridge structure of lanthanide catalytic systems was made in many works [66-69]. Nevertheless, the possibility must not be ruled out that active centres contain both types of bonds (tt-allyl and a-bridge). It is important that these bonds may differ dramatically in reactivities. In order to answer the question concerning the possible coexistence of two types of bonds, the polymerisation of butadiene on catalytic systems NdCl3 3L-AlR3, where R is /-C4H9 Ln is Nd or Tb L is TBP, prepared in the presence of a small amount of butadiene and piperylene [71, 72] was investigated. Table 3.3. 

Figure 3.1 Basic stages of growing reaction by polymerisation of bntadiene (R = R = H), isoprene (R = H and R = CH3) and piperylene (R = CH3 and R = H) nnder the action of catalytic system NdCl3-3TBP-Al (iC4Hc,)3.

The objective of this part of work was to study the role of the structure of the diene (butadiene, isoprene and piperylene) in the mechanism of regio- and stereoselectivity in polymerisation with the lanthanide catalytic system NdCl3-3TBP-Al(2-C4H9)3. To this... 

In the polymerisation of piperylene, when the CH2=CH(CH3) double bond of the diene comes closer to the Nd-C o-bond, the steric repulsion between the methyl groups of the terminal unit and the piperylene molecule appears (Figure 3.2a). Therefore, it is necessary to alter significantly the orientation of the terminal unit of the growing polymer chain, for example, to turn it about the Nd-C bond to decrease the repulsion of the methyl groups. 

Also note that, in accordance with the calculated data, the energies of the o-form of the piperylene active centre, in which the Nd atom is linked to the C atom, and the o-form of the centre in which the metal atom is bonded to the C, atom, differ slightly. The corresponding value of AE is maximal, when the terminal units are in the trans-cisoid conformation and is as low as 4 kj/mol. In the models of the butadiene centres, this difference is much greater (12.7 kJ/mol) [76], that is, in polymerisation of piperylene, the o-structure of the active centre with the Nd-C bond is realised more often than in the butadiene polymerisation. This accounts for why the total amount of 1,2- and trans-, A-units must be greater in the polymerisation of piperylene than in the polymerisation of butadiene, due to insertion via the Nd-C bond and the anti-syn isomerisation of the terminal unit. This was shown experimentally [82]. 

In the polymerisation of piperylene regioselectivity, addition of 1,4-units according to head-to-tail type, is caused by the fact that only the double bond of diene bearing no methyl substituent can react with the metal-carbon o-bond of the active centre. Involvement of the double bond of piperylene bearing the methyl substituent in the reaction of insertion is considerably hampered because of the steric repulsion between the methyl groups of the terminal unit of the growing chain and the diene. The smaller difference in energy between the two possible o-forms of the terminal unit in the polymerisation of piperylene, as compared to butadiene, is responsible for the increased lifetime of the active centre in the o-form, in which the Nd atom is linked to the atom. This results in an increased content of trans-1,2- and trans-1,4 units in polypiperylene. 

Method 2 The catalytic complex is prepared by the in situ method (two-component TiCl4-Al(2-C4H9)3 and three-component TiCl4-Al(/-C4H9)3-piperylene) and the solvent from tanks 1 and 2 (Figure 3.8) respectively, have been mixed in tubular turbulent device 3, at the minimal linear flow rate, in a diffuser of 0.5 m/s and the time of reactant passing through a reaction zone of 2-3 s (hydrodynamic impact on a catalytic system in the turbulent mode). The catalyst solution is then moved from device 3 to the vessel 4, where isoprene is then added and polymerisation is carried out. 

A similar dependency of catalyst dispersity can be observed in another microheterogeneous catalytic system based on the VOCl3-Al(i-C4H9)3 compound, which is widely used in isoprene and butadiene polymerisation processes. A substantial change of particle size in a two-component (V-Al) catalytic system, and the hydrodynamic impact on a catalytic system in a turbulent mode, is not observed with traditional process technology. A substantial decrease of catalyst particle size is observed after modification of the V-Al catalyst using piperylene additives. The hydrodynamic impact on the modified catalytic system results in an additional reduction of catalyst particle size. In addition, the particle size distribution for the Ti-Al catalyst narrows as it does for the V-Al catalyst. 

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...

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...

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)...

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...

Figure 3.40 Kinetic activity distribution of macromolecule growth centres in the isoprene polymerisation process with TiCl4-Al(/-C4H9)3-piperylene. 1) traditional method, and 2) hydrodynamic impact on the catalytic system. The yield is 20%...

Figure 3.43 The change of kinetic activity, 5, of different types of macromolecule growth centres I (1, 4), II (2, 5), and III (3, 6) in the isoprene polymerisation process with the TiCl4-Al(f-C4Hc,)3-piperylene catalyst. 1-3 - traditional method and 4-6 - formation of a catalytic system in the turbulent mode (Method 4)...

Piperylene oligomers (cationic oligomerisation, process terminating, and polymerisate washing) [7]. 

Figure 5.13 The scheme of SSOP liquid oligopiperylene rubber syntbesis. 1,2-reactor-polymeriser with gate agitators and condensers, 3 - degasator (a) 1,3-small-sized tubular turbulent devices for oligopiperylene synthesis and catalyst deactivation, 2 - condenser (b), 4 - receiver, 5 - degasator. I - solvent, II - catalyst, III - piperylene fraction, IV - deactivator, V - recycle, and VI - SSOP to stock...

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