Structural Developments in Synthetic Rubbers during Uniaxial Deformation by In Situ Synchrotron X-Ray Diffraction

The molecular orientation and strain-induced crystallization of synthetic rubbers - polyisoprene rubber, polybutadiene rubber, and butyl rubber [poly(isobutylene isoprene)] - during uniaxial deformation were studied with in situ synchrotron wide-angle X-ray diffraction. The high intensity of the synchrotron X-rays and the new data analysis method made it possible to estimate the mass fractions of the strain-induced crystals and amorphous chain segments in both the oriented and unoriented states. Contrary to the conventional concept, the majority of the molecules (50-75%) remained in an unoriented amorphous state at high strains. Each synthetic rubber showed a different behavior of strain-induced crystallization and molecular orientation during extension and retraction. Our results confirmed the occurence of strain-induced networks in the synthetic rubbers due to the inhomogeneity of the crosslink distribution. The strain-induced networks containing microfibrillar crystals and oriented amorphous tie chains were responsible for the ultimate mechanical properties.