Thermoplastic elastomers , glass transition temperature

The strategies used to produce block polymers can be well demonstrated with the example of a three-block polymer, (styrene)m(butadiene) (styrene)m, which is commercially available as a thermoplastic elastomer. This three-block polymer can best be produced in a two-stage process with bifunctional initiators. Sodium naphthalide or dilithium compounds can be used as initiators (see Section 18.1). Styrene is added on to the dianion produced, B , and SmBnS is formed. The initiators mentioned above, however, are only effective in tetrahydrofuran and other ethers. But butadiene blocks of only limited c/5-1,4 content are produced in these solvents, and this has an undesirable effect on the thermoplastic elastomer (glass transition temperature is too high). Consequently, well-dissolving aromatic dilithium compounds are preferably used in the presence of small amounts of aromatic... 

Engineering thermoplastics have glass-transition temperatures that fall in a wide temperature range, extending well above and below room temperature. Elastomers in the uncured state have glass-transition temperature well below room temperature. 

Ethylene-norbomene copolymers of interest as thermoplastics were discussed in Section 11.6.2. It is however to be noted that copolymers with a norbomene content of about 30 wt% have a glass transition temperature of about 0°C and that copolymers with norbomene contents up to this amount are being evaluated as thermoplastic elastomers... 

Table I serves to illustrate how the nature and size of the substituent attached to the P-N backbone can influence the properties of the poly(organophosphazenes). The glass transition temperatures range from -84 °C for (NP CH-CH ) to around 100 °C for the poly(anilinophosphazenes). Polymers range from elastomers to flexible film forming thermoplastics or glasses at room temperature.

T [Tick] free Tm TMPCl TPE o Glass transition temperature Concentration of free and uncomplexed TiCl4 Melting temperature 2-Chloro-2,4,4-trimethylpentane Thermoplastic elastomer Tensile strength... 

Before BASF investigated this product, Quirk and Hsieh [1], Yuki and coworkers [2,3] and Fischer [4] carried out investigations with this monomer. The first two used the anionic polymerization mechanism and Fischer tried to copolymerize this monomer using free radical polymerization. In the latter case the yields were very low. The use of S/DPE blocks in thermoplastic elastomers [5] has also been briefly described. Some of the work carried out at BASF has been published in a recent review article [6], Owing to the enhanced thermal properties of this copolymer in comparison with atactic polystyrene - the glass transition temperature increases up to 180 °C, depending... 

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. 

Table 5.5. Composition, pretreatment, crystallinity, glass transition temperature Tg and experimental and calculated microhardness values, Hg p, and Hgai and their difference AH = Hgai — Hg p for thermoplastic elastomers of PEE-or PEEC-type. 

The properties that define polymers as an elastomer are that they must be amorphous when unstretched and must be above their glass transition temperature to be elastic. This can be compared to thermoplastics that must be crystalline or must be used below this temperature to preserve dimensional stability. 

Developing biphasic materials in order to improve the fracture toughness of thermoset resins is now a common practice. Thermoplastics that have a high glass-transition temperature (Tg) are used as tougheners in preference to low-Tg elastomers because of their insignificant effect on the thermal and modulus properties. 

At this point, we had the first four of the seven characteristic features of A-B-A thermoplastic elastomers, as shown in the box. That is, we were completely confident that we had a three-block polymer, rubbery behavior with high tensile strength in the unvulcanized state, and also complete solubility. We concluded from these properties that these polymers were two-phase systems. We then generated the essentials of the two-phase, domain theory and visualized the physical structure illustrated schematically in Figure 1. We also visualized applications in footwear, in injection-molded items, and in solution-based adhesives. Positive confirmation of the two-phase structure quickly followed, by detection of two separate glass transition temperatures, as well as observation of the thermoplasticlike reversibility of bulk- and... 

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