Polybutadienes preparation

The molecular structure of polybutadiene prepared with BuLi and barium salts is greatly dependent on the presence of specific amounts of water and t-butanol used in the barium salt formation. The data in Figure 3 demonstrate that the greatest effect is obtained as the hydroxide content of the solution phase of the barium salt increased from 0 to 7.4 mole 7, Ba(0H)a. This particular salt results from a Hs0-t-butanol mixture containing 2.5 mole 7. water. The amount of trans-1,4 increased from 637, to 767, and accompanying this change the intrinsic viscosity increased from 1.60 to 5.22. The polymers were gel-free. 

The most important polymerization variables on which the molecular structure of polybutadienes prepared with Ba-Li catalysts depends are described as follows. 

Figure 4 shows that the amount of trans-1,4 structure is increased from 557, which is the trans-1,4 content of a polybutadiene prepared with BuLi alone in nonpolar solvents, to a maximum of about 807, trans-1,4 content for polybutadienes prepared at a mole ratio of barium salt to BuLi equal to 0.5. 

Figure 3. Effect of hydroxide content of Ba t-butoxide-hydroxide on the molecular structure of polybutadiene prepared in toluene at 30°C.

Catalyst Concentration. The concentration of the catalyst has a marked effect on the trans-1,4 content of polybutadienes prepared with BuLi and barium t-butoxide-hydroxide in toluene at 30°C, as shown in Figure 5. The trans-1,4 content increases with a decrease in the molar ratio of the initial butadiene to BuLi concentration [(M)/(BuLi)]. The trans-1,4 content approaches a limiting value of about 807., for polybutadienes prepared with large amounts of this catalyst. 

Polymerization Temperature. The stereoregularity of polybutadienes prepared with the BuLi-barium t-butoxide-hydroxide catalyst in toluene is exceedingly temperature dependent. Figure 6 compares the trans-1,4 dependence for polybutadiene prepared with BuLi, alone, and with the BuLi-barium t-butoxide-hydroxide complex in toluene (the molar ratio of the initial butadiene to BuLi concentration was 500). The upper curve demonstrates that the percent trans content increased rapidly from 627. to 807. trans-1,4 as the temperature decreased from 75°C to 22°C. From 22°C to 5°C, the microstructure does not change. The increase in trans-1,4 content occurred with a decrease in cis-1,4 content, the amount of vinyl unsaturation remaining at 5-87.. For the polybutadienes prepared using BuLi alone, there is only a very slight increase in the trans-1,4 content as the polymerization temperature is decreased. 

The amount of both low and high molecular weight polymer produced, as a function of polymerization temperature, can be seen in Figure 7. In this Figure, the MWD s of polybutadienes prepared with barium t-butoxide-hydroxide and BuLi in toluene at 30°C and 5°C are compared. Although both polymers show a broad MWD, the fraction of low molecular weight polymer present in the polybutadiene prepared at 5°C is greatly decreased. 

The polybutadienes prepared with these barium t-butoxide-hydroxide/BuLi catalysts are sufficiently stereoregular to undergo crystallization, as measured by DTA ( 8). Since these polymers have a low vinyl content (7%), they also have a low gl ass transition temperature. At a trans-1,4 content of 79%, the Tg is -91°C and multiple endothermic transitions occur at 4°, 20°, and 35°C. However, in copolymers of butadiene (equivalent trans content) and styrene (9 wt.7. styrene), the endothermic transitions are decreased to -4° and 25°C. Relative to the polybutadiene, the glass transition temperature for the copolymer is increased to -82°C. The strain induced crystallization behavior for a SBR of similar structure will be discussed after the introduction of the following new and advanced synthetic rubber. 

The stereoregularity of butadiene based polymers prepared in cyclohexane with Ba-Mg-Al catalysts depends on polymerization temperature and catalyst concentration. Trans-1,4 content increases nonlinearly with a decrease in polymerization temperature over the range of 80° to 30°C (Figure 11) and/or a decrease in the initial molar ratio of butadiene to dialkyl-magnesium from 3400 to 400 (Figure 12). For polybutadienes prepared with relatively large amounts of catalyst at 30°C, the trans-1,4 content approaches a limiting value of about 907.. 

Figure 3. The effect of temperature on microstructure of polybutadiene prepared...

Tristar polybutadienes prepared by the intermediacy of lithium acetal initiators were also converted to three dimensional networks in a liquid rubber formulation using a diisocyanate curing agent. Table IV shows normal stress-strain properties for liquid rubber networks at various star branch Hn s. It can be seen that as the branch Mn increases to 2920, there is a general increase in the quality of the network. Interestingly, the star polymer network with a star branch Mn of 2920 (Mc=5840) exhibits mechanical properties in the range of a conventional sulfur vulcani-zate with a Me of about 6000-8000. 

It is interesting to note that the microstructure of the polybutadiene prepared by us at 30°C is... 

Graver, J.T., Kraus,G. Rheological properties of polybutadienes prepared by n-butyl-lithium initiation. J. Polymer Sci. Pt. A 2,797-810 (1964). 

C-NMR spectroscopy has shown that the polybutadienes prepared using alkyl-lithium initiators have random placement of the different modes of enchainment 222-223). This contrasts with an earlier claim of blocky structures 224). Random sequence distribution has also been established for polyisoprene by 1H-NMR 225) and 13C-NMR 226) spectroscopy. 

Reaction of cw- 1,4-Poly butadiene and PVC. Et2AlClt-Cobalt Compound Catalyst. Commercial cw-1,4-polybutadiene prepared with a Et AlCl-cobalt compound catalyst system was freed of antioxidant by solution in benzene and precipitation with methanol. The cis-1,4,polybutadiene had an intrinsic viscosity in benzene at 25 °C of 2.4 and a greater than 96% cis-1,4 content. 

Et2AlCl Catalyst. Under the same conditions as above 20 grams of PVC and 2 grams of cis-1,4-polybutadiene, prepared with an alkyl-aluminum-titanium tetraiodide catalyst system (95% cis-1,4 content, intrinsic viscosity at 25°C in benzene 2.2) in 200 ml chlorobenzene were allowed to react in the presence of 2 mmoles of Et2AlCl at 5°-10°C for 60 minutes. The reaction product was isolated by precipitation in methanol and dried to yield 22.0 grams of modified poly (vinyl chloride). Hexane extraction under reflux for 24 hours removed 8% of hexane-soluble material. 

A few other pertinent observations have been made. Although the effect of temperature on structure in the case of sodium or potassium metal polymerized butadiene was shown to lead to the gradual approach to a nearly random mixture between 0 and 45° (41,32), in the case of phenyllithium in tetrahydrofuran there is observed only a few percent difference between — 78° and + 100° (76). Furthermore, the use of lithium, n-butyllithium, n-amyllithium or isoamyllithium produces polyisoprene of the same microstructure in tetrahydrofuran (77). Kuntz (34) found that polybutadiene prepared with n-butyllithium in... 

These results are consistent with Natta s (362) earlier finding that there was no carbon-14 in cis-polybutadiene prepared from (14C2H5)2A1C1 + + cobalt bisacetylacetonate. However, Natta (362), Cooper (363) and Duck (364) considered that propagation occurred at an organo-cobalt bond. 

However, the structural identity of polybutadienes prepared with bis(7r-crotylnickel chloride) and with (C4H7NiX)2+ Lewis acids system suggests that the nature of the active sites is similar for these catalysts. 

The microstructure of polybutadienes prepared with w-allylnickel complexes does not depend on the details of monomer coordination if one of the double bonds is involved (1,2- or trans-1,4-structures) or both (cis-1,4 structure). This fact is confirmed by results obtained with homogeneous catalytic systems based on (C4H7NiCl)2 and GaCl3 in... 

The termination reactions appear to be quantitative and specific for the reaction of saturated polymer molecules attached to aluminium and titanium [116], but applied to diene polymerizations the method is less satisfactory mainly because of the greater stability of allylic carbon-transition metal bonds. Polybutadiene has been labelled by terminating with tritiated methanol with the Cr(acac)3/AlEt3 catalyst [55], and similarly polyisoprene prepared with VCl3/AlEt3 [107]. Polybutadiene prepared with Til4/Al(i-Bu)3 has been labelled using C02 [115]. 

Table I indicates the microstructure of polybutadienes prepared by means of the indicated catalyst systems. It shows that at some given ratio of components, not necessarily at all ratios, a particular catalyst system is capable of yielding polymer with the indicated structural composition. The patent literature, in some cases, contains conflicting data, indicating the influence of unspecified, and pos-sibly unknown, factors.

The dependence of the polymer microstructure on the ratio of catalyst components is related to the nature of these components. The structure of polybuta-diene obtained with an aluminum triisobutyl (AIBU3)-titanium tetrachloride catalyst system is a function of the Al/Ti molar ratio (Table II). Polybutadiene prepared at Al/Ti ratios of 0.5 to 8 in benzene or heptane and at 3° or 25° C. contain at least 90% 1,4- units. Polymerizations carried out at ratios of 1.0 and less at 25° C. in heptane and at ratios of 1.25 or less at 3° C. in heptane or benzene give crystalline polymers containing more than 96% trans-, A- structure (6). A similar temperature dependence of polymer structure has been reported in the polymerization of butadiene with a diethylcadmium-titanium tetrachloride catalyst system (3). Polybutadiene obtained with a triethylaluminum-titanium tetrachloride catalyst system at a 0.9 Al/Ti ratio at 30° C. in benzene is reported to contain 67% cis-1,4- units (19). 

The polymerization of butadiene with an aluminum trialkyl-titanium tetra-iodide catalyst system apparently yields a polybutadiene containing more than 85% cis-1,4- structure (19). The limited amount of data available does not cover a sufficiently wide range of Al/Ti ratios to permit the drawing of conclusions analogous to those drawn in the case of the trans-l,4-polybutadienes. However, as shown in Table III, over the range of Al/Ti ratios from 1.5 to 5.0, the polybutadiene prepared in benzene at 30° C. contains 85 to 93% cis-1,4-, 3 to 11% tram-1,4-, and 3 to 5% 1,2- structures. 

Fe compounds have received much less significant attention than Ni or Co compounds as the diene polymerization catalyst. FeEt2(bpy)2 catalyzes cyclodimerization of 1,3-butadiene [79] and polymerization of vinyl monomers such as acyclic ester [80]. Recently, FeEt2(bpy)2/MAO was found to show high catalytic activity toward 1,2-polymerization of 1,3-butadiene and 3,4-polymerization of isoprene at -40 to +25 °C (Eq. 14) [81]. The crystalline polybutadiene prepared below 0 °C is composed of... 

Next in importance is the polymerization of butadiene, if the use of sodium is ignored in the production of such inorganic compound as sodium cyanide, sodium peroxide, and titanium. Buna rubber, prepared by the sodium-catalyzed copolymerization of butadiene and styrene, was of considerable importance during World War II, especially in Germany. More recently, Morton s alfin catalyst has caught the attention of the rubber industry because of the exceptional quality of polybutadiene prepared by his techniques. 

The microstructures of polybutadienes prepared withZiegler-Natta catalysts vary with catalyst composition. It is possible to form polymers that are high either in 1,2 placement or in 1,4 units. The catalysts and the type of placement are summarized in Table 5.7. 

Table 5.7. Microstructures of Polybutadienes Prepared with Ziegler-Natta Catalysts ...

How are high molecular weight polybutadienes prepared and used ... 

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