Thermoplastic elastomers studies

Botterhuis NE, Karthikeyan S, Veldman D, Meskers SCJ, Sijbesma RP (2008) Molecular recognition in bisurea thermoplastic elastomers studied with pyrote-based fluorescent probes and atomic force microscopy. Orem Commun 2008(33) 3915-3917... 

Wegner, G., et ai, Structure and properties of segmented polyether-esters. II. Crystallization behavior of polyether-esters with random distribution of hard segment length. Die Angewandte Makromolekulare Chemie, 74(1) p. 295.1978. Litvinov, V.M., et ai, Phase Composition of Block Copoly(ether ester) Thermoplastic Elastomers Studied by Solid-State NMR Techniques. Macromolecules, 36(20) p. 7598.2003. 

Dardin A, Boeffel Ch, Spiess H-W and Stadler R (1994) Orienration behavior of thermoplastic elastomers studied by 2H-NMR and FT-IR spectroscopy, Polym Mater Sci Eng 71 248-249. 

The synthesis of well defined block copolymers exhibiting controlled molecular weight, low compositional heterogeneity and narrow molecular weight distribution is a major success of anionic polymerization techniques 6,7,14-111,112,113). Blocks of unlike chemical nature have a general tendency to undergo microphase separation, thereby producing mesomorphic phases. Block copolymers therefore exhibit unique properties, that prompted numerous studies and applications (e.g. thermoplastic elastomers). 

World Thermoplastic Elastomers, Freedona Industry Study, 2002, 1553. 

George, R.S. and Joseph, R., Studies on thermoplastic elastomers from polypropylene and latex waste products, Kautsch. Gummi Kunst., 47, 816, 1994. 

Polymer structure and formulation. As an example, Woo et al. [7] measured OIT values for series of commercial PVC resins and polyester thermoplastic elastomers (TPEs). The researchers used the ASTM D3895-80 procedure, but substituted air as the oxidising gas instead of pure oxygen. A dependency on thermal processing history of the TPE film samples appeared to influence the measured OIT in the PVC study, chemically different chain ends affected polymer stability and hence OIT values. 

Shape Change of Structural Entities. In many cases the growing anisotropy is not only a phenomenon of rotating structural entities, but also goes along with a deformation of the structural entities themselves. This case will be studied here. Only affine deformations shall be discussed. In practice, such processes are observed while thermoplastic elastomers are subjected to mechanical load, but also while fibers are spun. 

IR spectroscopy can be used to characterise not only different rubbers, but also to understand the structural changes due to the chemical modification of the rubbers. The chemical methods normally used to modify rubbers include hydrogenation, halogenation, hydrosilylation, phosphonylation and sulfonation. The effects of oxidation, weathering and radiation on the polymer structure can be studied with the help of infrared spectroscopy. Formation of ionic polymers and ionomeric polyblends behaving as thermoplastic elastomers can be followed by this method. Infrared spectroscopy in conjunction with other techniques is an important tool to characterise polymeric materials. 

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). 

Segmented thermoplastic elastomers exhibit structural heterogeneity on the molecular, the domain, and in some cases on a larger scale involving periodic or spherulitic texture. Each level of structural organization is studied by specific methods. Molecular sequence distributions can be studied by chemical methods, such as NMR or IR spectroscopy. 

Figure 21.4 Corrected melt viscosity as a function of shear stress and temperature for the three block copolymers studied. Reproduced with permission from Legge, Holden and Schroeder, Thermoplastic Elastomers A Comprehensive Review, Hanser Verlag, Munich, 1987...

Two PBT based thermoplastic elastomers were studied. One was a PBT-polytetrahydrofuran (pTHF) copolymer (PECO-1) and the other one a PBT-poIy(propylene glycol) (PPG) copolymer (PECO-2). In both cases the degradations were done on 30 pm thick films. All of these polymers were supplied by DSM Engineering Plastics. 

Ethylene propylene copolymers and their blends exhibit diverse degradation behavior under the influence of light, heat and radiation. In spite of many papers in this area, little, if any, mechanistic data on degradation and stabilization of this important class of materials is available in the literature. The present paper reviews the published literature in this area organised under five distinct class of materials, namely, thermoplastic, elastomeric, and heterophasic copolymers, thermoplastic elastomer and blends. Of this, elastomeric ethylene-propylene copolymers appears to have been most exhaustively studied. Very few studies have reported on thermoplastic copolymers, both random as well as heterophasic as well as thermoplastic elastomers and blends. Specific mechanisms of degradation and stabilization of each of these classes of materials are discussed. 

Practically no studies of degradation have been carried out on thermoplastic elastomers. 

Copoly(ester ester)s belong to the family of thermoplastic elastomers (TPEs) and consist in general of thermo-reversible hard and elastic soft domains [11]. The copoly(ester ester) used here consists of 60% poly(butylene terephthalate), 35% poly(butylene adipate) and 5% 4,4 -methylenebis(phenyl isocyanate), and shows domain sizes of about 20 nm [12]. The material possesses a rubber plateau between the glass transition temperature of the mixed amorphous PBA/PBT phase (the PBT phase is semi-crystalline) at about -30°C and the melting point of the PBT at about 220°C. Due to the vulnerability of the amorphous PBA/PBT soft domains towards water attack [13] the PBT/PBA copoly(ester ester) is used here to study the existence of ESC of a chemical rather than a physical nature. For the sake of clarity it should be emphasized that no additives have been used in the copoly(ester ester) described here. 

Micromechanical studies have been carried out on thermoplastic elastomers. The latter are a special class of multiphase systems (block copolymers) exhibiting an unusual combination of properties they are elastic and at the same time tough and they show low-temperature flexibility and strength at relatively high temperatures (frequently ca 150 °C). In addition, they are easily processable. For this reason, they are nowadays of great commercial importance as engineering materials. In natural... 

The microhardness of films of thermoplastic elastomers based on PBT-cyclo-aliphatic carbonate (PBT-PCc) block copolymers has also been studied (Giri et al, 1997). The microhardness of the amorphous films has been discussed in terms of a model given by the additivity values of the single components and It... 

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