Elastomers Hytrel

In Chapters 3 and 11 reference was made to thermoplastic elastomers of the triblock type. The most well known consist of a block of butadiene units joined at each end to a block of styrene units. At room temperature the styrene blocks congregate into glassy domains which act effectively to link the butadiene segments into a rubbery network. Above the Tg of the polystyrene these domains disappear and the polymer begins to flow like a thermoplastic. Because of the relatively low Tg of the short polystyrene blocks such rubbers have very limited heat resistance. Whilst in principle it may be possible to use end-blocks with a higher Tg an alternative approach is to use a block copolymer in which one of the blocks is capable of crystallisation and with a well above room temperature. Using what may be considered to be an extension of the chemical technology of poly(ethylene terephthalate) this approach has led to the availability of thermoplastic polyester elastomers (Hytrel—Du Pont Amitel—Akzo). 

The effect of °Co y-ray irradiation on the mechanical properties, surface morphology, and fractography of blends of plasticized PVC and thermoplastic copolyester elastomer, Hytrel (E.I. Du Pont de Nemours Company, Inc., Wilmington, Delaware), have been studied by Thomas et al. [445]. Radiation has two major effects on the blend cross-linking of the Hytrel phase and degradation of PVC phase. Both effects are found more prominent at higher radiation dose. 

Elastic PVC articles are inferior in comparison to vulcanized rubbers used for production of corrugated pipe articles regarding their tensile and tear strengths, and deterioration of their flexibility with time of use. This was improved by multilayer material. Three layered material gave the best performance. The outer layer was made out of polyester elastomer (Pelprene P-70B), the inner layer from polyester elastomer (Hytrel HTG-4275), and the intermediate layer from PVC having formulation given in the above table. 

A segmented thermoplastic elastomer, Hytrel 5526 (HT), as a flexible filler is added to PET phase to modify the rheological behavior of PET/PE MRCs [34]. The flexibility of the microbrils with low HT loading has no obvious influence on the viscosity of MRCs. With the increase of HT content, especially for the 30 wt% HT, the microfibrils flexibility increases, causing the viscosity of MRCs to have a slight decreasing trend shown in Figure 12.19. Moreover, the more flexible microfibrils lead to lower melt elasticity of MRCs. 

Telechelic macromers have often been used for making block copolymers. Thus the elastomic fibre, spandex (e.g. Lycra), is made from poly-THF, H(0(CH2)4) 0H, with a diisocyanate (to form a urethane), and the thermoplastic elastomer, Hytrel, is composed of blocks of poly-THF and terephthalic esters. Non-ionic surfactants are often block copolymers of polyethylene oxide/polypropylene oxide (prepared by anionic polymerization). 

The SAE J200/ASTM D2000 classification only covers crosslinked elastomers. Hytrel, Alcryn and the other thermoplastics are included for comparison. 

Solid-liquid biphasic systems have been developed with many different resins/polymers as the solid phase, usually selected after an extensive screening. The highest productivities have been obtained with the polyester elastomer Hytrel 8206 (20.4 gl with K. marxianus) [82] and with several macroporous... 

The viscosity versus shear rate data for polyester elastomer (Hytrel) were obtained from its technical brochure on rheology and handling suf lied by the manufacturer [81] (Table B2 of Appendix B). The data covered a shear-rate range of 10-3000/s for five different grades of Hytrel. For three of the grades, the data temperature was 220 C, whereas for the other two grades, they were 180 C and 240 C, respectively. A total of 20 data points were used [77] in the unification process to obtain the master rheogram for polyester elastomer (Hytrel) shown in Fig. 4.35. 

PTMO is used as a flexible segment in most of the commercial PEE elastomers (Hytrel , DuPont Elitel , Elana, etc.) [1,2]. The PTMO segments of molecular weight higher than 1500 g/mole tend to crystallize causing a decrease in the rubbery phase content in the material. The use of copolymers, e.g., PTMO with PEO and PTMO with PPrO, allows to preserve the amorphous polyether phase structure [23]. Since the copolymerization of PTMO with PPrO [24] or... 

Noncrystalline aromatic polycarbonates (qv) and polyesters (polyarylates) and alloys of polycarbonate with other thermoplastics are considered elsewhere, as are aHphatic polyesters derived from natural or biological sources such as poly(3-hydroxybutyrate), poly(glycoHde), or poly(lactide) these, too, are separately covered (see Polymers, environmentally degradable Sutures). Thermoplastic elastomers derived from poly(ester—ether) block copolymers such as PBT/PTMEG-T [82662-36-0] and known by commercial names such as Hytrel and Riteflex are included here in the section on poly(butylene terephthalate). Specific polymers are dealt with largely in order of volume, which puts PET first by virtue of its enormous market volume in bottie resin. 

A smaller but rapidly growing area is the use of PTMEG ia thermoplastic polyester elastomers. Formation of such polyesters iavolves the reaction of PTMEG with diacids or diesters. The diols become soft segments ia the resulting elastomeric materials. Examples of elastomeric PTMEG polyesters iaclude Hytrel (Du Pont) and Ecdel (Eastman Chemicals). 

Poly(pivalolactone) 739 Table 25.12 Propenies of Hytrel-type thermoplastic elastomers... 

With these polymers hard blocks with T s well above normal ambient temperature are separated by soft bloeks which in the mass are rubbery in nature. This is very reminiscent of the SBS triblock elastomers discussed in Chapter 11 and even more closely related to the polyether-ester thermoplastic elastomers of the Hytrel type deseribed in Chapter 25. 

Thermoplastic polyester elastomers such as the Du Pont product Hytrel were developed later than the polyurethane materials, being first introduced in 1972. They have similar characteristics to the polyurethanes but there is an upward shift in the hardness range (i.e. the softest grades are not so soft, but the hardest grades are harder than the corresponding extreme grades in the polyurethanes). 

Hytrel Bulletin 1-25, Blends of Hytrel polyester elastomer with PVC, E.I. DuPont de Nemours and Co., Delaware, 1976. 

The Material of the Example. Poly(ether ester) (PEE) materials are thermoplastic elastomers. Fibers made from this class of multiblock copolymers are commercially available as Sympatex . Axle sleeves for automotive applications or gaskets are traded as Arnitel or Hytrel . Polyether blocks form the soft phase (matrix). The polyester forms the hard domains which provide physical cross-linking of the chains. This nanostructure is the reason for the rubbery nature of the material. 

The interest of that type of material has been largely demonstrated, f.i. by the Hytrel-type of products (i.e. polyether-ester multiblocks), particularly in the field of thermoplastic elastomers thanks to the efficient cross-linking action of the harder blocks. Due again to the swift development of increasingly sophisticated catalytic techniques, more and more original achievements... 

Other important thermoplastic elastomers are the multiblock polyetheresters (trade names Hytrel, Lomod) and polyetheramides (trade names Pebax, Estamid, Grilamid). 

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