Brittle-ductile transition under compression of glassy polymers*

Polymeric glasses of high molecular weight are always ductile in compression. Even the most brittle (in tensile extension) polystyrene is ordinarily ductile in uniaxial compression. Thus, it seems that theoretical studies only need to develop a description of yielding and post-yield plastic deformation for polymer glasses. But can yielding take place in compression if the molecular weight is sufficiently reduced? In other words, can alpha processes be greatly accelerated during external deformation in absence of chain networking? Must a new paradigm account for the role of chain networking that only takes place in polymers of high molecular weight? To address these questions, we systematically explored the response over a range of temperature to uniaxial compression at different rates of polystyrene with various molecular weights and molecular weight distributions. Our preliminary results [1] show that PS of low molecular weight is brittle in compression and chain networking is necessary (but not sufficient) to ensure a ductile response. [1] Liu, J.; Lin, P.; Cheng, S.; Wang, W.; Mays, J. W.; Wang, S.-Q. Polystyrene glasses under compression: Ductile and brittle responses. \textit{ACS Macro Letters }\textbf{2015}, 1072-1076.