Polybutadiene, isomers

Figure 9.36 Raman spectra of polybutadiene-polystyrene copolymer in the C=Cstretching region showing three distinct bands of polybutadiene isomers cis-1,4 at 1650 cm-1, trans-1,4 at 1665 cm-1 and syndiotactic-1,2 at 1655 cm-1 (a) spectrum from the center of sample and (b) spectrum from the edge of sample. (Reproduced with permission from G. Turrell and J. Corset, Raman Microscopy, Developments and Applications, Academic Press, Harcourt Brace Company, London. 1996 Elsevier B.V.)...

The structures corresponding to the polybutadiene isomers, which can be evaluated as it is detailed in the next section, are shown in Figure 7. 

Budene solution polybutadiene (solution polymerized) is cis-1,4-poly(butadiene) produced with stereospecific catalysts which yield a controlled MWD, which is essentially a linear polymer. Butadiene rubber, polybutadiene, is solution-polymerized to stereospecific polymer configurations " by the additional polymerization of butadiene monomer. The following cis- and trans-1,4-polybutadiene isomers can be produced cis-1,4-polybutadiene with good dynamic properties, low... 

Hydrogenation of polybutadiene converts both cis and trans isomers to the same linear structure and vinyl groups to ethyl branches. A polybutadiene sample of molecular weight 168,000 was found by infrared spectroscopy to contain double bonds consisting of 47.2% cis, 44.9% trans, and 7.9% vinyl. After hydrogenation, what is the average number of backbone carbon atoms between ethyl side chains ... 

Commercially, anionic polymerization is limited to three monomers styrene, butadiene, and isoprene [78-79-5], therefore only two useful A—B—A block copolymers, S—B—S and S—I—S, can be produced direcdy. In both cases, the elastomer segments contain double bonds which are reactive and limit the stabhity of the product. To improve stabhity, the polybutadiene mid-segment can be polymerized as a random mixture of two stmctural forms, the 1,4 and 1,2 isomers, by addition of an inert polar material to the polymerization solvent ethers and amines have been suggested for this purpose (46). Upon hydrogenation, these isomers give a copolymer of ethylene and butylene. 

Fig. 2. To and We for isomers of polybutadiene and polyisoprene, and for typical average isomeric compositions in styrenic block copolymers.

TDI isomers, 210 Tear strength tests, 242-243 TEDA. See Triethylene diamine (TEDA) Telechelic oligomers, 456, 457 copolymerization of, 453-454 Telechelics, from polybutadiene, 456-459 TEM technique, 163-164 Temperature, polyamide shear modulus and, 138. See also /3-transition temperature (7)>) Brill temperature Deblocking temperatures //-transition temperature (Ty) Glass transition temperature (7) ) Heat deflection temperature (HDT) Heat distortion temperature (HDT) High-temperature entries Low-temperature entries Melting temperature (Fm) Modulu s - temperature relationship Thermal entries Tensile strength, 3, 242 TEOS. See Tetraethoxysilane (TEOS)... 

The yield of cross-linking depends on the microstructure of polybutadiene and purity of the polymer as well as on whether it is irradiated in air or in vacuum. The cross-link yield, G(X), has been calculated to be lowest for trans and highest for vinyl isomer [339]. The introduction of styrene into the butadiene chain leads to a greater reduction in the yield of cross-linking, than the physical blends of polybutadiene and polystyrene [340]. This is due to the intra- and probably also intermolecular energy transfer from the butadiene to the styrene constituent and to the radiation stability of the latter unit. 

Even if a same azide is used as the sensitizer, such properties of the photoresist as photosensitivity, photocurability and adhesion to base surfaces differ depending on the property of the base polymer. That is, degree of cyclization, content of the unsaturated groups and molecular weight of the polymer affect the photoresist properties mentioned above. H.L.Hunter et al. have discussed the dependence of the sensitivity of polybutadiene photoresist on the polymer structure, and have concluded that a higher sensitivity was obtained when 1,2- and 3, -isomers were used( 7.) ... 

Butadiene can form three repeat units as described in structure 5.47 1,2 cw-1,4 and trans-, A. Commercial polybutadiene is mainly composed of, A-cis isomer and known as butadiene rubber (BR). In general, butadiene is polymerized using stereoregulating catalysts. The composition of the resulting polybutadiene is quite dependent on the nature of the catalyst such that almost total trans-, A, cis-, A, or 1,2 units can be formed as well as almost any combination of these units. The most important single application of polybutadiene polymers is its use in automotive tires where over 10 t are used yearly in the U.S. manufacture of automobile tires. BR is usually blended with NR or SBR to improve tire tread performance, particularly wear resistance. 

Polyisoprene is composed of four structures as shown in Equation 5.48. As in the case of polybutadiene, it is the cis-, A structure that is emphasized commercially. The cA-1,4-polyisoprene is similar to the cw-l,4-polybutadiene material except it is lighter in color, more uniform, and less expensive to process. Polyisoprene is composition-wise analogous to NR. The complete cw-1,4 product has a Tg of about —71°C. Interestingly, isomer mixtures generally have higher Tg values. Thus, an equal molar product containing cA-1,4 trans-, A, and 3,4 units has a Tg of about —40°C. 

The polymer ra-l,4-polybutadiene (Tg = 170 K) is more flexible and has a lower Tg than trans- 1,4-polybutadiene (Tg = 190 K), and in general this is true of all geometric isomers. 

SBR is the most widely used synthetic elastomer. It is an amorphous random copolymer consisting of a mixture of l.2, cis and trans isomers. Cold SBR produced at —20 C consists of 17% 1,2. 6% cis and 77% trans isomers of polybutadiene. This commercial product has a Tt of -60 C, an index of refraction of 1.534S, and a coefficient of linear expansion of 66 X 10 s cm/ cm C. Because of the high percentage of the trans isomer, it is less flexible and has a higher heat buildup, when flexed, than Hevea rubber. Although carbon black-filled or amorphous silica-filled SBR has useful physical and mechanical properties, the SBR gum rubber is inferior to Hevea rubber. 

Calculations. The spectrum of a typical high cis-1,4 polymer sample is shown before and after irradiation in Figure 1 and that of a trans-1,4 polymer film in Figure 2. The significant infrared bands are listed in Table II for all of the polybutadienes, with the assignments to the various modes of molecular oscillation as developed by Binder (2). The bands used to estimate quantitative changes in the olefin groups were those at 740 cm."1 for the cis isomer, 967 cm."1 for the trans isomer, and 910 cm."1... 

Spectra have been recorded of the following polymers Poly isobutylene. Schaufele has reported a spectrum of a non-turbid specimen of this material complete with depolarization data (18). Bands at Av - 2919 and 720 cm 1 are clearly polarized and must result from symmetrical modes. Schaufele was also able to show that the short chain hydrocarbon CH3(CH2)12CH3 could be examined satisfactorily but the results were very much sharpened by cooling to liquid air temperatures. Polyisoprene and Polybutadiene. Both of these in the cis form have also been examined at Southampton very recently. The trans isomers gave no spectra due to fluorescence but no interpretation has been attempted as yet. Spectra are shown in Fig. 7 and 8. 

Microstructure of polybutadienes refers to the percentage of cis, trans, and vinyl isomers. These were unavoidably variable because of the catalyst systems used (13) 2-98% cis, 1-76% trans, and 1-22% vinyl isomer. The vinyl contents of each sample are given in Table I for the purpose of light-scattering experiments. 

Another type of geometric arrangement arises with polymers that have a double bond between carbon atoms. Double bonds restrict the rotation of the carbon atoms about the backbone axis. These polymers are sometimes referred to as geometric isomers. The X-groups may be on the same side (cis-) or on opposite sides (trans-) of the chain as schematically shown for polybutadiene in Fig. 1.12. The arrangement in a cis-1,4-polybutadiene results in a very elastic rubbery material, whereas the structure of the trans-1,4-polybutadiene results in a leathery and tough material. Branching of the polymer chains also influences the final structure, crystallinity and properties of the polymeric material. 

The coordination catalysts were quickly extended to dienes and found to produce the long-sought objective of a "synthetic natural rubber, i.e., cis-1,4-polyisoprene. cis-1,4-Polybutadiene was also quickly produced. These were, and still are, erroneously referred to as stereo rubbers. They are actually unique geometric isomers rather than stereoisomers, but the name stereo rubber became established probably because of the relationship in time and catalyst usage to stereo olefin polymerization. 

Since isomerically pure polymers were not available, three different kinds of BR, each relatively high in one of the three kinds of base units were used as standards [35]. The band near 1308 cm 1 was identified [38,39] with the cis isomer and used for analyses [43]. The 1308 cm 1 band is weak and relatively broad, with the appearance of an unresolved doublet (1306,1311 cm 1). The cis band at 730 cm 1 is more frequently used in spite of some difficulties. Relatively pure, crystalline stereoregular polymers have been prepared and structures were determined by X-ray diffraction for cis [44], trans [45] and syndiotactic vinyl [46] and isotactic vinyl [47]. Infrared spectra [48-50] have been published for the four stereoregular polybutadienes, with detailed analyses of the spectra and band assignments for cis [51], trans [51] and syndiotactic vinyl [51] polymers. For the spectrum of isotactic vinyl BR, bands at 1232, 1225, 1109, 943, 876, 807 and 695 cm"1... 

The determination of percentage of styrene and butadiene isomer distribution in copolymers is an extension of the methods for the analysis of polybutadiene. The styrene band at 700 cm 1 is largely independent of the sequence distribution and therefore useful in styrene content determination [76]. A series of bands in the IR spectrum of crystalline isotactic polystyrene at 758, 783, 898, 920, 1053, 1084, 1194, 1261, 1297, 1312 cm"1 have been attributed to the helical structure [77]. The absorption bands for butadiene in SBR are similar to BR structures (Table 3.2a). 

In previous publications (7,14, 17) it was presumed that the microstructure of the ultimate unit of the polybutadiene chain arose from the mode of its attachment to the central atom in the 7r-allylic complex, so that the syn (or anti) isomer yielded trans- (or cis)-1,4-enchainment. 

The graft polybutadiene containing both styrene and acrylonitrile prepared in a separate experiment was isolated by a double precipitation. The experimental value for the degree of grafting was calculated on the basis of the trans isomer of polybutadiene (Figure 17). Except for two fractions, the styrene contents are within the shaded band. We note that both the styrene and the acrylonitrile contents increase slightly. This phenomenon might be caused by the polymerization temperature which was lower than in the previous two experiments (100°C. instead of 110°C.). 

POLYBUTADIENE WAS CALCUL D BASED ON THE TRANS ISOMER ONLY... 

As in any other chemical compound, different geometrical arrangements of substituent groups are possible in a polymer where rigid molecular units are involved. This gives rise to trans- and cis-configurational isomerism in polymers containing double bonds in their repeat units, as in polyacetylene and natural and synthetic rubbers. The structures of the trans- and m-isomers of polyacetylene and polybutadiene are illustrated in Fig. 1.8. 

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