Absorption spectra polybutadiene

Analysis The tin content in the polybutadiene was measured by atomic absorption analysis. The molecular weight was measured by GPC analysis. The number average-molecular weight was determined by GPC measurement based on polybutadiene. The microstructure of polybutadiene was measured by an IR absorption spectrum method (Morero method). 

Figure 5 shows the infrared absorption spectrum of the non-modified polybutadiene. The peak at 740 cm is based on the cis-1.4 structure of polybutadiene, and those at 910 cm and at 960 cm are based on the vinyl structure and the trans-1,4 structure, respectively. From these results, the microstructure of the polybutadiene was determined as follows the cis-1.4 content was 97.4X and the trans-1,4 and vinyl contents were 1.2X and 1.4X, respectively. 

Figure 5. Infrared absorption spectrum of non-modified polybutadiene...

During UV irradiation in air (oxygen) the absorption spectrum of styrene-butadiene rubbers (SBR) (Fig. 3.59) changes rapidly, in a way similar to that of polybutadiene (cf Fig. 3.58). This change is caused by carbonyl groups aliphatic (<300nm), aromatic or a,/ -unsaturated ketones and aldehydes (>300nm)p93]. 

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). 

The ir spectrum of trans-1,4-polybutadiene (TB) after photosensitized oxidation (Figure 2) likewise displays a growth of the 2.9-/jim band. However, there was no significant change in intensity of the 10.3-/un trans band, nor was there any development of a new cis band at ca. 14.0 /jim. Thus any shifted double bonds in TB as in Reaction 1 are essentially all-trans. An interesting feature of Figure 2 is the growth of the 6.0-/jim absorption which is clearly not caused by C=C stretch of cis double... 

After 10-min irradiation, the ir spectrum of the trans-polypentenamer film showed the expected weak 2.9 /x peak (O-H) without the 5.8 absorption (C=0), by analogy to 102-reacted 1,4-polybutadiene (20). Only minor changes in the spectrum were noted after decay of the chemiluminescence. In contrast to this result, the chemiluminescence from polymer films oxidized at 100 °C or singlet-oxygenated in solution and cast into films usually was invariant at 25 °C for several hours. 

Figure 24. The difference spectrum of a cured polybutadiene sample, showing the 965 cm absorption band of the trans Isomer. The difference spectrum was obtained by substractlon of the components determined by least squares from the said mixture.

Figure 3.17 contains the difference spectrum between ATH and ATH which had been coated, from solution, with the same grade of MPBD. In this spectrum relatively weak adsorptions at 1860 cm and 1781 cm are present indicating some unreacted MPBD, but in addition a strong peak at 1700 cm exists which corresponds to the absorption frequency of the carbonyl stretch in the carboxylic acid. Clear evidence that the anhydride has hydrolysed, but the lack of a strong peak at 1580 cm, the carbonyl stretching frequency of the salt, shows that the acid had not reacted with the surface of the ATH to form salt bridging between the polybutadiene backbone and the filler surface. 

The difference in intensities observed for various compositions of a particular type of copolymer may be used to determine the composition of the copolymer, that is, the relative amounts of each monomer unit present. In the simplest case, where a particular band is due solely to one component of the copolymer, then either the absorptivity may be determined or a calibration graph constructed for this purpose. For systems where a band position free from the absorptions of other components of the copolymer cannot be found, a slightly lengthier approach is required. The absorptivities at various suitable locations in the spectrum must be determined for each component and then, by taking measurements for a variety of concentrations of the components in the copolymer at these different locations, equations can be constructed to determine the composition of an unknown copolymer. An example of this approach is the determination of the individual isomers of butadiene copolymers, cw-1,4-, trans-XA- and 1,2-polybutadiene. From the solution spectra (using a suitable solvent such as carbon disulphide) of the individual components, which may be obtained separately, the absorptivities of each isomer may be determined at suitable points in the spectrum of the copolymer and hence used directly in the three equations required for the quantitative determination. In a similar manner, the isomer compositions of isoprene and chloroprene may be determined. 

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