Stretch-Induced Crystallization and Phase Transitions of Poly(dimethylsiloxane) at Low Temperatures: An in Situ Synchrotron Radiation Wide-Angle X-ray Scattering Study

Stretch-induced crystallization (SIC) and phase transitions of poly(dimethylsiloxane) (PDMS) have been studied with the in situ synchrotron radiation wide-angle X-ray scattering technique (WAXS) during tensile deformation at temperatures ranging from −45 to −65 °C. The phase transitions during tensile deformation go through different processes at different temperature regions, where four phases are involved in namely oriented amorphous (OA), mesophase, α form, and β form crystals. We found that SIC of the α form can proceed via two different multistage ordering processes with either the mesophase or β form as the structural intermediate. Further cyclic tensile experiments demonstrate that the transition from the β to α form is a reversible process controlled by stress, which is attributed to the different helical pitches in β and α forms. A nonequilibrium phase diagram of SIC and phase transitions are constructed in strain–temperature space, which is of great significance for practical applications of PDMS at low temperature.