Hytrel thermoplastic elastomers

Hytrel thermoplastic elastomer (/) is composed of m poly(butylene terephthalate) hard segments and n poly(tetramethyleneoxy) terephthalate soft segments. The hard and soft segments are assumed to be random in distribution. The ratio of m/n controls the mectonical properties of the copolymer (2). 

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. 

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). 

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. 

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). 

Du Font s Hytrel copolyester thermoplastic elastomers are slightly higher in price than the polyurethane types and have grown rapidly. They have a wide range of service temperatures and have found major uses in recreational vehicles, belting, hydraulic hose, and mechanical goods. 

Thomas and co-workers [1986] studied effects of gamma-irradiation on a thermoplastic elastomer, TPE, a polyether-ester block copolymer from 1,4-butanediol, polybutylene glycol and terephthalic acid (Hytrel D40), TPE, and its blends with PVC, in air, at doses of 1, 10, 100 and 500 kGy. Visual inspection of the samples showed no color change up to 500 kGy, but the samples irradiated at 500 kGy showed surface cracks. 

Dupont (2007) Addit. Polym., 2007, 2. DupPont (2013) DuPont Hytrel Thermoplastic Polyester Elastomer, http //plastics. dupont. com/plastics/dsheets/hytrel/ GBHYTREL3078.pdf GXHC gx session id =6cSJ32S70 (accessed 29 September 2014). 

Figure 8.57 Elastic modulus in compression vs. temperature for DuPont Hytrel thermoplastic polyester elastomer resins [7].

Hytrel Thermoplastic polyether-ester block copolymer elastomers, 1,4-butanediol-polybutylene glycol-terephthalic acid copolymer, TPE E. I. du Pont de Nemours... 

TP-EE Thermoplastic elastomer - ether ester Arnitel Hytrel TP-EPDM... 

Segmented polyurethanes (TPU) and thermoplastic polyester elastomers such as Hytrel by du Pont are also important thermoplastic elastomers. 

T. Nishi, T. K. Kwei, and T. T. Wang, Physical Properties of Poly (vinyl chloride)-Copolyester Thermoplastic Elastomer Mixtures, /. Appl. Phys. 46, 4157 (1975). PVC/copolyester thermoplastic elastomer thermoplastic IPN. Modified Hytrel materials. 

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). 

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