Hydrogenous atactic polystyrene

Deuterated SPS (d-SPS) was prepared by polymerizing dg-styrene with Cp / methylaluminoxane (MAO) or CpTiCh catalysts in the laboratory, and usual hydrogenous atactic polystyrene (h-APS) was purchased from Aldrich Chemical their characteristics are summarized in Table 17.1. 

TABLE 17.1 Characteristics of Deuterated SPS and Hydrogenous Atactic Polystyrene... 

In polystyrene, a benzene ring replaces one hydrogen atom of each ethylene monomer unit. Because such a ring is bulky, atactic polystyrene does not crystallize to any significant extent. The most familiar application of this polymer is in the polystyrene foam used in disposable containers for food and drinks and as insulation. A volatile liquid or a compound that dissociates to gaseous products on heating is added to the molten polystyrene. It forms bubbles that remain as the polymer is cooled and molded. The gas-filled pockets in the final product make it a good thermal insulator. 

The large difference between the scattering lengths of hydrogen (b = —3.74 X 10" cm) and deuteriiun (b = 6.67 x 10 cm) offers a means of manipulating the contrast, and it forms the basis of all conformational studies in bulk. The pioneering experiments carried out in the 1970s on atactic polystyrene (PS) and PMMA confirmed Hory s hypothesis that polymer dimensions in bulk are unpermrbed and follow the expected dependence. 

The IR absorption spectrm of synthetic polymers is generally simple. In Figure 17.22 we illustrate the polystyrene spectrum, which is fairly representative of aromatic hydrogen polymers. The polystyrene spectrum s three IR bands appear sharply in the spectrum without ambiguity at 2850,1603, and 906 cm . The bands above 3000 cm are due to unsaturated C H stretching vibrations. The stretching vibration of conjugated C=C appears around 1600 cm . The presence of the 760-and 700-cm bands are attributed to C H deformations. Monosubstitution is confirmed by the pattern of weak bands from 2000 to 1600 cm . Atactic polystyrene has bands at 670,620,565 (shoulder), and 536 cm. Isotactic polystyrene does not have any absorption from 550 to 500 cm or at 670 cm . The... 

If a vibration involves hydrogen bonding, or is affected by the conformational changes that occur, then the band may be very broad. On the other hand, if the band is relatively insensitive to external influences then the band may be quite sharp. For example, the spectrum of high density polyethylene (HOPE) has relatively sharp bands when compared with that of low density polyethylene (LDPE). The spectrum of non-crystalline, atactic polystyrene has bands due to the aromatic ring which are relatively sharp whereas other bands tend to be a little broader than for the crystalline, isotactic form. 

Figure 3. HREELS spectra of (a) 70% isotactic hydrogenated polystyrene, (b) atactic fully deuterated polystyrene.

In conclusion, it was found from the SANS experiments that the change in tacticity of d-PS, that is, from atactic to syndiotactic, results in the decrease of miscibility of deutrated polystyrene (d-PS) with hydrogenous polystyrene (h-PS). 

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