The Relationship between Craze Structure and Molecular Weight in Polystyrene as Revealed by mSAXS Experiments Nikolaos E. Zafeiropoulos,* 1 Richard J. Davies,* 2 Konrad Schneider, 1 Manfred Burghammer, 2 Christian Riekel, 2 Manfred Stamm 1 1 Leibniz Institute of Polymer Research Dresden, Hohe Strasse 6, Dresden 01069, Germany E-mail: zafeiropoulos@ipfdd.de 2 European Synchrotron Radiation Facility, BP 220, F-38043 Grenoble Cedex, France E-mail: rdavies@esrf.fr Received: June 30, 2006; Revised: August 1, 2006; Accepted: August 7, 2006; DOI: 10.1002/marc.200600453 Keywords: craze; polystyrene; SAXS Introduction It is well known that the deformation of thermoplastic glasses prior to fracture can be divided into four distinct regimes; elastic and inelastic deformation, shear yielding, and craz- ing. [1] Crazing involves a large degree of plastic deformation localized within very thin zones and is widely regarded as a source of toughening. However, the formation of crazes has also been linked to the onset of brittle fracture, which leads to catastrophic failure. Considering these relationships, and the interest in optimizing the mechanical performance of poly- mers, it is of no surprise that crazing has received considerable attention by several research groups. One unique feature of crazing is that, unlike shear yielding, which occurs with almost no change in bulk volume, crazing involves a signi- ficant volume increase, often several times before catastrophic failure occurs. [2] The structure of crazes has been previously established through a series of experiments with transmission Summary: The phenomenon of crazing in polymers has received considerable attention in the past as it is thought to play a pivotal role in determining the performance of poly- mers under load. One aspect of particular interest has been the interconnection between molecular structure, craze charac- teristics, and macromechanical properties. In the present study, three different grades of polystyrene (PS) with dif- ferent molecular weights have been systematically inves- tigated in situ with synchrotron radiation microfocus small- angle X-ray scattering (mSAXS). The results suggest that there are different mechanisms operating in PS samples with low and very high molecular weights, compared to those of medium-to-high molecular weight. Previously it was thought that, above the critical molecular weight of entanglement, the effect of molecular weight on PS’s mechanical behaviour at room temperature was negligible. Craze evolution as a function of strain in PS. Macromol. Rapid Commun. 2006, 27, 1689–1694 ß 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim Communication DOI: 10.1002/marc.200600453 1689