Polymers thermoplastic behavior

EPDM-Derived Ionomers. Another type of ionomer containing sulfonate, as opposed to carboxyl anions, has been obtained by sulfonating ethylene—propjlene—diene (EPDM) mbbers (59,60). Due to the strength of the cross-link, these polymers are not inherently melt-processible, but the addition of other metal salts such as zinc stearate introduces thermoplastic behavior (61,62). These interesting polymers are classified as thermoplastic elastomers (see ELASTOLffiRS,SYNTHETIC-THERMOPLASTICELASTOLffiRS). 

Elastomeric polypropylenes with thermoplastic behavior can be prepared from conformationally dynamic metallocenes such as bis(2-arylindenyl)zirconium dichlorides. These can exist in two conformations in the course of the chain lifetime a chiral rac isomer which is stereodirecting and an achiral meso isomer which is aspeciflc. The resulting polymer consists of blocks of isotactic polypropylene alternating with runs of atactic material (equation 12). 

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... 

Poly(aryl ketones) (PEEK, PEK, and PEKK) are commercial high temperature polymers offering an excellent combination of properties combined with thermoplastic behavior. Poly(aryl ether ketone) PAEK blends have been reviewed by Harris and Robeson [1989]. Miscibility with PEI (Ultem 1000 GE) and other PI containing isopropylidene bridging units was noted. Arzak et al. [1997] reviewed the performance ofPEEK/PEI blends and noted a synergistic behavior in ductility and impact strength as reported earlier. Utility of these blends as a thermoplastic matrix candidate for advanced composites has been proposed [Harris and Robeson, 1989 Davis et al., 1992]. 

It should be quite apparent that, although all major architectural polymer classes are derived from common or related repeat units, the covalent connectivity is truly discrete and different. Furthermore, mathematical analysis of the respective propagation strategies clearly illustrates the dramatic differences in structure development as a function of covalent bond formation. It should be noted that linear, branched, and dendritic topologies differ substantially both in their covalent connectivity, as well as their terminal group to initiator site ratios. In spite of these differences, these open, unlooped macromolecular assemblies clearly manifest thermoplastic polymer type behavior in contrast to the looped, bridged connectivity associated with cross-linked, thermoset systems. In fact, it is now apparent that these three open assembly-topologies (i.e., (I) linear, (III) branched. 

Finally, the use of flexible ligands for designing ID lanthanide coordination polymers could be of interest as far as the synthesis of polymers with interesting optical properties and exhibiting a thermoplastic behavior is considered. 

Thermoplastic behavior Thermoplastic polymers Thermosetting polymers Vegetable fibers... 

The strategies presented so far in this chapter rely on a common concept polymers with a network structure based on reversible covalent bonds. Healing is permitted by a temporary transition from a thermoset state to a thermoplastic behavior with enough chains mobility at ambient temperature. Considering this, alternative routes based on the same concept could be... 

It should be emphasized that the molecular theories presented in this chapter are valid only for flexible homopolymers and thus they cannot describe the rheological behavior of stmctured polymer systems, including multicomponent and/or multiphase polymers, such as block copolymers, liquid-crystalline polymers, thermoplastic polyurethanes, immiscible polymer blends, highly filled polymers, and nanocomposites. We discuss this subject in the remaining chapters of this volume. 

Upon associating a Voigt element and a Maxwell element in series, one obtains the Bni ers model, which is well-suited to describe the creep behavior of a thermoplastic polymer the behavior of such a material is characterized by an instantaneous elasticity followed by a phase of retarded elasticity, but the strain retains in this case an irreversible character. 

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