Frans-Polybutadiene

In the polymerization of butadiene, Teyssie (52-54) has shown that certain electron donors, such as alcohols or phosphines, can convert tt-allylnickel chloride from a catalyst which forms c/j-polybutadiene to one which produces frans-polybutadiene. These ligands presumably block a site on the nickel atom, forcing the butadiene to coordinate by only one double bond. While alcohols cannot be added directly to the hexadiene catalyst (as they deactivate the alkylaluminum cocatalysts), incorporation of the oxygen atom on the cocatalyst places it in an ideal position to coordinate with the nickel. The observed rate reduction (52) when the cri-polybutadiene catalyst is converted into a fra/w-polybutadiene catalyst is also consistent with the observed results in the 1,4-hexadiene synthesis. 

We studied the effect of high surface area carbon black and fused silica fillers on the large, secondary glass transition of non-crystallizable SBR (31.6% styrene) copolymer which is associated with small main-chain motions of frans-polybutadiene units (25). Figure 4 shows plots... 

Fig. 6 DSC analysis of 1,4-frans-polybutadiene in the bulk phase. The two endotherms correspond to the crystal-crystal transition at 70 °C and to the melting point at 133 °C...

Motional and mesomorphic states were found in 1,4-frans-polybutadiene included in nanochannels after formed in situ by solid state polymerization in the matrix of perhydrotriphenylene (PHTP) (Fig. 13) [48],... 

Rg. 13 (a) Projection of PHTP crystal structure along the channel axis, the polymer chains are omitted for clarity (b) Crystal structure of 1,4-frans-polybutadiene in the PHTP inclusion compound... 

Ba/Mg/Al catalyst system discussed above can be readily converted into a variety of functional end groups. One of the most useful and widely used functionalization reactions is hydroxyethylation using ethylene oxide, as shown in Fig. 14. Here, a mono-hydroxyl-terminated high-fran polybutadiene was prepared by adding a small amount of ethylene oxide to a solution of carbanions, followed by hydrolysis. This particular example demonstrates the ability to attach hydroxyl groups molecularly to a crystalline polybutadiene. The use of a bifunctional diorganomagnesium could provide a very useful tele-chelic polymer for further extension to form a rubber network. 

Table 1. Second virial coefficient of l,4-frans -polybutadiene. ...

The ROMP method was extended to synthesize cyclic polybutadiene using 1,5-cyclooctadiene (COD) or 1,5,9-frans-czs-frans-cyclododecatriene (CDT)... 

The determination of the microstructure of polybutadiene, i.e., the distribution of cis and frans-1,4-polybutadiene, as well as that of trans-XA- and 1,2-polybutadiene in polystyrene presents an analytical challenge. Fig. 5.1-12 shows the spectrum of a mixture of polystyrene and polybutadiene, obtained in CS2 solution. Difference spectroscopy with pure polystyrene as a standard affords the spectrum of the polybutadiene fraction, from which the microstructure can easily be determined (Peitscher, 1979). 

Kamiya et al. [33] studied diffusion of seven hydrocarbons (w-butane, wobutane, 1-butene, cw-2-butene, fran -2-butene, isobutylene, 1,3-butadiene) in two rubbery polymers 1,2-polybutadiene and ethylene-vinyl acetate copolymer. The observed diffusion coefficients were compared with the sizes of diffusing molecules, estimated from molar volumes of liquid hydrocarbons, and shown to decrease regularly with increasing molecular size (see Figure 9.6) ... 

Polybutadiene, CAS 9003-17-2, is a common synthetic polymer with the formula (-CH2CH=CHCH2-)n- The cis form (CAS 40022-03-5) of the polymer can be obtained by coordination or anionic polymerization. It is used mainly in tires blended with natural rubber and synthetic copolymers. The trans form is less common. 1,4-Polyisoprene in cis form, CAS 9003-31-0, is commonly found in large quantities as natural rubber, but also can be obtained synthetically, for example, using the coordination or anionic polymerization of 2-methyl-1,3-butadiene. Stereoregular synthetic cis-polyisoprene has properties practically identical to natural rubber, but this material is not highly competitive in price with natural rubber, and its industrial production is lower than that of other unsaturated polyhydrocarbons. Synthetic frans-polyisoprene, CAS 104389-31-3, also is known. Pyrolysis and the thermal decomposition of these polymers has been studied frequently [1-18]. Some reports on thermal decomposition products of polybutadiene and polyisoprene reported in literature are summarized in Table 7.1.1 [19]. 

Pyrolysis results for a polybutadiene sample phenyl terminated (45% wt. vinyl) with Mn = 1,000 and about 10% frans-1,4 and 5% c/s-1,4 is shown in Figure 7.1.2. The pyrolysis was done in similar conditions with the other polybutadiene sample. The peak identification for the pyrogram is given in Table 7.1.3... 

Competitive Sulfonation of cis-l,4-Polyi8oprene Model (PIP) vs. cis OT frans-l,4-Polybutadiene (c-PBD or t-PBD) Model Compounds in Decalin Solution... 

However, the excellent cold properties of the lithium polymer can be explained on the basis of microstructure in Table II. It seems reasonable to assume that of the three possible microstructures the 1,2 structure is the least desirable for low temperature flexibility followed by the frans-1,4 structure, with the cis-1,4 structure the most desirable. A comparison of the low temperature flexibility of balata (or gutta-percha) vs. Hevea rubber would indicate a preference for the cis-1,4 structure over the trans-1,4 structure, although these natural products are polyisoprenes rather than polybutadienes. In the case of the 1,2 structure, it is generally assumed that the prevalence of this structure in sodium-catalyzed polybutadiene, or butadiene copolymers, accounts for its poor cold properties however, the occurrence of a natural or synthetic product with an entirely 1,2 structure would help to confirm this more definitely. The relative predominance of any single structure is another important consideration in the performance of a rubber at low temperatures because a polymer with a large percentage of one structure would be more likely to crystallize at a low temperature. 

Polytetrafluoroethylene and fran -1,4-polybutadiene are two examples of macro-molecular condis crystals. The heat capacity of polytetrafluoroethylene is shown in Fig. 2.63, that of fran -l,4-polybutadiene is illustrated in Fig. 2.112. Both polymers... 

Conventional prefixes indicating cis and trans isomers are placed in front of the polymer name. An example is cZs-1,4-polybutadiene, or in frans-l,4-polyisoprene. 

FIGURE 17.2 Structures of stereoregular 2-substituted (isoprene-like) polybutadienes (R = alkyl or aryl group) (a) ds-1,4-polymer (b) fran -1,4-polymer (c) isotactic 1,2-polymer (d) syndiotactic 1,2-polymer (e) isotactic 3,4-polymer (f) syndiotactic 3,4-polymer. 

A strain-crystallizing material like NR shows much better autohesion. It can be processed to a relatively low viscosity for easy wetting on contact, and still exhibit green strength due to strain-induced crystallization. Several other strain-crystallizable elastomers have been synthesized and shown to exhibit autohesion and green strength comparable or superior to that of NR. These include rran.s-polypen-tenamer, fran -butadiene-piperylene elastomers, and uranium-catalyzed polybutadiene. 

Polybutadiene is also produced in low volume as specialty products. These include low-molecular-weight, liquid 1,2-polybutadienes (60-80%, 1,2 content) used as potting compounds for transformers and submersible electric motors and pumps, liquid frans-1,4-polybutadienes used in protective coatings inside metal cans, and hydroxy-terminated polybutadiene liquid resins for use as a binder and in polyurethane and epoxy resin formulations. 

Figure 6 The frans-l,4-polybutadiene chain in the planar, alhrraws conformation. This (highly disfavored) form is shown for convenience in enumerating atoms and bonds of the chain (reproduced by permission of the American Chemical Society from...

If, however, the phenylene rings are para-oriented, the chains retain their axial symmetry and can crystallize more readily. Similarly, double bonds in trans configuration maintain the chain symmetry thus allowing for crystallite formation. This is highlighted by a comparison of the amorphous elastomeric ds-polyisoprene (Tm=28°C) with highly crystalline frans-polyisoprene (T = 74°C), which is a nonelastomeric rigid polymer, or ds-1,4-polybutadiene (T = —11°C) with trans-1,4-polybutadiene (7j =148°C). 

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