Morphology, elastomers crystallinity

Pig. 1. Interpenetrating network morphology of thermoplastic elastomer where A = the crystalline domain, B = the junction of crystalline lamellae, and... 

Morphological features for POPs can range from low-temperature elastomers (when aliphatic alkoxy substituents of different length are attached to the polyphosphazene skeleton), to crystalline, film- and fibre-forming materials... 

Thermoplastic tri-block copolymers are interesting since they possess novel properties different from those of the homo- or copolymers. The thermoplastic elastomers have many of the physical properties of rubbers, i.e., softness, resilience, and flexibility. The unique properties of this kind of copolymer are due to the microphase separation of the hard crystalline domains dispersed in a continuous amorphous matrix (Fig. 6). Such phase morphology provides a physical network of flexible chains cross-linked by crystalline microdomains. The advantages over natural vulcanized rubbers are that thermoplastic elastomers are readily soluble in an appropriate solvent and can be processed as thermoplastics [109],... 

Figure 7-6. Simplified morphology of a thermoplastic elastomer. A-B-A triblock copolymer has amorphous elastomeric B blocks (solid curves) between high Tg or crystalline outer blocks (jagged lines). Circles represent crystallites or domains of high Tg outer blocks.

Other Classification Criteria. Other levels of classification should be superimposed on the above. These include latex, suspension, and bulk type syntheses, all of which result in different properties of the final materials. Uses of plastic-forming and elastomer-forming monomers and crystalline and amorphous structures must be distinguished. The tacticity of the polymers is sometimes important. Of course, the ratio of both polymer masses dictates the overall morphology. Physical operations such as swelling, annealing, and orienting must be considered in any complete treatment. 

The process involves transesterification (catalyst, 200 °C) followed by polycondensation (250 °C, second stage. Morphological studies show the presence of crystalline (mp 190-200 °C) polyester lamellae in a continuous amorphous phase. In contrast to the A-B-A thermoplastic elastomers where the domains are formed from amorphous polystyrene segments, the domains here are formed from crystalline hard segments containing the 1,4-glycol polyester moiety. 

S. Saikrasun, S. Bualek-Limcharoen, S. Kohjiya, and K. Urayama. Thermotropic liquid-crystalline copolyester/thermoplastic elastomer in situ composites. I. Rheology, morphology, and mechanical properties of extruded strands. J. Appl. Polym. ScL, 89 2676-2685, 2003. 

Saikrasun S, Bualek-Limcharoen S, Kohjiya S, Urayama K. Thermotropic liquid-crystalline copolyester (Rodrun LC3000)/thermoplastic elastomer (SEBS) in situ composites II. Mechanical properties and morphology of... 

The underlying morphology will have a large effect on the physical properties. The soft phase is usually the continuous phase to maintain the elastomeric behavior of the material. In materials that have crystalline hard segments, such as copolyesters and polyurethanes, both phases are essentially continuous. Thermoplastic elastomers almost never have the soft segment as the isolated phase and the hard segment as the continuous phase. The most... 

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