Strain-induced crystallization, elastomeric networks

Kloczkowski, A. Mark, J. E. Sharaf, M. A. Erman, B., Theory of Strain-Induced Crystallization in Real Elastomeric Networks. In Synthesis, Characterization, and Theory of Polymer Networks and Gels, Aharoni, S. M., Ed. Plenum Press New York, 1992 pp 227-241. 

Strain-induced crystallization also has a pronounced reinforcing effect within the network, and this increases the ultimate strength and maximum extensibility (26). The capability of crystallizing with extension while remaining elastomeric at low elongations provides an important self-reinforcement mode for natural rubber. The only other elastomer with these properties is cis-polybutadiene. These materials are the elastomers of choice for many heavy-duty applications. 

Mark, J.E. (1979) Effect of strain-induced crystallization on the ultimate properties of an elastomeric polymer network. Polymer Eng. ScL, 19, 6,409. 

Su T-K, Mark JE. The effect of strain-induced crystallization on the elastomeric properties of c 5-1,4-polybutadiene networks. Macromolecules 1977 10 120-5. 

Elastomeric chains of sufficient regularity may crystallize under some conditions. The deformation of a macromolecule is accompanied by a decrease in its conformational entropy. Its tendency to crystallize is therefore increased. The oriented system will crystallize even above the melting point of the isotropic system (and is thus strain-induced crystallization ). The crystallinity reaches a value which depends on the degree of deformation and the crystallization temperature. The melting point = Ai/ /ASm, given by the ratio of the enthalpy of fusion to the entropy of fusion, is thus increased by the network deformation. 

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