Thermoplastic elastomers structural analysis

The physical interactions in TPE can be characterised by IR spectroscopy. A few examples of such studies are discussed here. Examples of PE based thermoplastic elastomers are NR/PE blends [50, 52]. TPE [49] based on 50/50 NR/LDPE, forms co-continuous morphological structure of both NR and LDPE. Thermal analysis shows that the blend is immiscible and from IR spectra of the 50/50 NR/LDPE blends [53], it is observed, the peaks of NR and PE exist almost in the same positions in the blend with a very little shift (Figure 5.12). The absorption band at 833 cm"1 for cis >C = C in NR (Figure 5.12) is shifted to 836 cm 1. Similarly the peak at 1370 cm"1 (C-H stretching of CH3 group) shifts to 1373 cm"1, while the peak for C=C double bond shifts from 1660 cm"1 to 1658 cm"1, and the band at 1467 cm"1 for -CH2 in LDPE (Figure 5.12) is shifted to 1462 cm 1. The spectra thus confirm that there exist only physical interactions in NR-PE blend. 

The above thermal analysis studies demonstrated the enhanced thermal stability of POSS materials, and suggested that there is potential to improve the flammability properties of polymers when compounded with these macromers. In a typical example of their application as flame retardants, a U.S. patent39 described the use of preceramic materials, namely, polycarbosilanes (PCS), polysilanes (PS), polysilsesquioxane (PSS) resins, and POSS (structures are shown in Figure 8.6) to improve the flammability properties of thermoplastic polymers such as, polypropylene and thermoplastic elastomers such as Kraton (polystyrene-polybutadiene-polystyrene, SBS) and Pebax (polyether block-polyamide copolymer). 

The properties of the linear material 7.27 and the network copolymer 7.28 have been studied by dynamic mechanical analysis, DSC, and transmission electron microscopy. Evidence was obtained for the formation of highly ordered micro-phase-separated superstructures in the solid state from the materials 7.27. The Cu(bipy)2 moieties appear to form ordered stacks, and this leads to thermoplastic elastomer properties. In contrast, the network structure of 7.28 prevents significant microphase separation [51-53]. By means of related approaches, dinuclear Cu helical complexes have also been used to create block copolymers by functioning as cores [54], and polymer networks have also been formed by using diiron(II) triple helicates as cores for the formation of copolymers with methyl methacrylate [55]. 

The network structure of unfilled and filled elastomers was probed by the analysis of the quadrupolar splitting in H solid echo spectra of uniaxially strained samples (55) (see Fig. 6). The local chain order at a given elongation is larger by a factor of 1.5-2 in the filled system. A decrease of local chain mobility in the absorption layer is observed under stress. The same method was applied to investigate molecular dynamic in thermoplastic elastomer based on hydrogen bonding complexes (61,62). 

Stribeck N and Fakirov S (2001) Three-Dimensional Chord Distribution Function SAXS Analysis of the Strained Domain Structure of a Poly(ether ester) Thermoplastic Elastomer, Macromolecules 34 7758-7761. 

Stribeck, N., Fakirov, S. Three-dimensional chord distribution function SAXS analysis of the strained domain structure of a poly(ether ester) thermoplastic elastomer. Macromolecules 34, 7758-7761 (2001)... 

SAXS and WAXS are particularly efficient in the study of amorphous polymers including microstructured materials, hence their use in block copolymers (see also Chapters 6 and 7). The advent of synchotron sources for X-ray scattering provided new information, particularly on the evolution of block copolymer microstructures with time resolution below one second. In particular, the morphology of TPEs is most often studied with these techniques Guo et al. [108] applied SAXS to the analysis of the phase behavior, morphology, and interfacial structure in thermoset/thermoplastic elastomer blends. WAXS is often associated with SAXS and some other methods, such as electron microscopy, and various thermal and mechanical analyses. It is mainly used in studies of the microphase separation [109,110], deformation behavior [111], and blends [112]. 

For anisotropic samples, such as thermoplastic elastomers showing uniaxial orientation, the analysis of the longitudinal structure gives only a fraction of the total information concerning the nanostructure topology. By analogy with the IDF concept, the complete information should be displayed in a multidimensional function that maps the distances between all the domain surfaces. 

---