Styrene-isoprene sample

Figure 7. Variations of tiie storage and loss moduli with frequency obtained from the analysis of the response of the material to a periodic modulation, for the styrene isoprene sample. Comparison with the macroscopically determined ones.

Figure 12.4 Cliromatograms of a styrene-isoprene-styrene tiiblock copolymer sample (a) microcolumn SEC trace (b) capillary GC ti ace of the inti oduced section x . Peak identification is as follows 1, ionol 2, not identified 3, Iiganox 565. Reprinted with pennission from Ref. (12).

Important examples of the ABA type are the styrene-butadiene-styrene (SBS) and styrene-isoprene-styrene (SIS) triblocks in which the outer blocks of the glassy styrene are much shorter than the inner elastomeric blocks. The usual phase arrangement of these materials is shown schematically in fig. 12.13. SBS copolymers have two glass-transition temperatures, as expected for a segregated structure, at —90 and -1-90 °C. The morphology depends on the precise composition and on the method of preparation samples of SBS containing either cylinders in a hexagonal array or spheres in a body-centred cubic array have been obtained. 

Jackson and Walker [7] studied the applicability of pyrolysis combined with capillary column GC to the examination of phenyl polymers (e.g., styrene-isoprene copolymer) and phenyl ethers e.g., bis[w-(w-phenoxy phenoxy)phenyl]ether. In the procedure the polymer sample is dissolved in benzene. The pyrolysis Curie point temperature wire is dipped 6 mm into the polymer solution. The polymer-coated wires are then placed in a vacuum oven at 75-80 °C for 30 minutes to remove the solvent. Figure 6.2 shows a characteristic pyrogram of the copolymer (isoprene-styrene) resulting from a 10-second pyrolysis at 601 °C. When the polyisoprene is pyrolysed, C2, C3, C4, isoprene, and CjoHig dimers are produced. When PS is pyrolysed, styrene and aromatic hydrocarbons are the products. Figure 6.2 shows that the copolymer product distribution and relative area basis resemble the two individual polymer product distributions. 

The actual temperature acquired by the sample during pyrolysis can be monitored using optical pyrometry or can be standardized between different pyrolyzers using a model compound. The procedure is based on the dependence of the composition of the pyrolysis products on temperature. One such compound chosen as a standard is an isoprene/styrene copolymer, trade name Kraton 1107 [15] (see Section 4.2). 

The effect of surface constraints on the morphology of the star-block copolymers was studied by Thomas and coworkers [337]. Thin film droplets of samples with various functionalities were studied, and the ones that exhibited the OBDD structure in the bulk were found to be cylinders in this case. In an independent study, the lamellar domain spacings of 4-arm and 12-arm star-block copolymers of styrene and isoprene were found, by TEM and SAXS, to be the same as those of the arm material [338]. 

In view of the wide application of Py—GC in industry and research, the development of techniques and equipment for automatic analysis by this method is of great practical interest. An automatic Py—GC system was developed by Coulter and Thompson [69] for Curie-type cells with a filament for specific application in the tyre industry. A typical analysis involves the identification and determination of polymers in a tyre material sample. The material of a tyre is essentially a mixture of polymers, most often natural rubber (polyisoprene), synthetic polyisoprene, polybutadiene and butadiene-styrene copolymer. A tube is normally made of a material based on butyl rubber and a copolymer of isobutylene with small amounts of isoprene. In addition to the above ingredients, the material contains another ten to twelve, such as sulphur, zinc oxide, carbon black, mineral oil, pine pitch, resins, antioxidants, accelerators and stearic acid. In analysing very small samples of the tyre material, the chemist must usually answer the following question on the basis of which polymers is the tyre made and what is their ratio The problem is not made easier by the fact that cured rubber is not soluble in any solvent. 

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