Noncrystallizable

The strength and extensibility of a noncrystallizable elastomer depend on its viscoelastic properties (28,29), even when the stress remains in equilibrium with the strain until macroscopic fracture occurs. In theory, such elastomers have a time- or rate-independent strength and ultimate elongation, but such threshold quantities apparently have not been measured, though rough estimates have been made (28,30). 

Here, v and v are the molar volumes of the repeating unit and a segment of the noncrystallizable first component, respectively. At the melting temperature T), of the second polymer component in the blend... 

For homogeneous blends, % < 0 and consequently the presence of another noncrystallizable polymer depresses the melting point of a polymer. 

Hydroxyl-terminated POET chains are end-linked into noncrystallizable trifunctional networks using an aromatic triisocyanate. The networks thus obtained are studied with regard to their stress-strain isotherms. The analysis of the temperature coefficient of PDET in terms of the RIS model confirms the results obtained from NMR studies, according to which the gauche states... 

In addition to conferring transparency on these polymers, the amorphous noncrystallizable nature of polysulfones assures minimal shrinkage during fabrication of the resins into finished parts. The absence of crystallinity also assures dimensional stability during the service life of the parts where high use temperatures are encountered. Good dimensional stability is important to many structural and engineering applications. 

Polymerization of nonsymmetrical cyclic molecules gives stereochemi-cally variable polymers, [-SiRR 0-] , analogous to the totally organic vinyl and vinylidene polymers [-CRR CH2-] . In principle, these polymers can be prepared in the same stereoregular forms (isotactic and syndiotactic) that have been achieved for some of their organic counterparts 1, 17). Unfortunately, the stereoregular forms have not been prepared, and only the stereoirregular form (atactic) has been obtained. Unlike the other two stereochemical forms, the atactic form is inherently noncrystallizable. 

Aliphatic polyesters may present a crystalline a process, and as a consequence the notations (3 and y are adopted for the glass-rubber and subglass relaxations, respectively. Although fully amorphous polymers cannot be achieved by quenching, it is possible to obtain polyesters with different degrees of crytallinity by copolymerization with a noncrystallizable diol. For example, the polyester of 1,6-hexanediol condensed with adipic acid is about 60% crystalline, while the polyester of this diacid with 2,5-hexanediol is completely amorphous. By varying the l,6-hexanediol/2,5-hexanediol... 

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