Phase Transition and Degradation Characteristics of Poly(urethane-Siloxane) Copolymers

Abstract

Poly(urethane-siloxane) (PU-Si) copolymers consisting of soft and hard phases presented a two-phase structure when analysed by differential scanning calorimetry. The copolymers showed a narrow glass transition region of soft segment between −116 °C and −119 °C and a narrow breadth of this transition within 3 °C. Both results indicated that the copolymers had a high degree of phase separation. The stress-strain curves showed that the copolymer with high phase separation exhibited low tensile strength. The hard phase presented several endothermic regions above room temperature. The first and second endothermic regions, which can be regarded as a short-range ordering and a long-range ordering respectively, appeared at about 60~120 °C and 160~200 °C. An endothermic peak appeared at around 200 °C which was attributable to a crystalline region. Two-stage degradation of copolymers was clearly observable in thermogravimetric analysis (TGA). Although the degradation of the copolymers was similar to that of typical polyurethane (PU), the shoulder of the derivative thermogram (DTG) curve was different. To examine this unique shoulder, the copolymers were examined using a slower heating rate. There were four stages of degradation, which was again different from the behaviour of PU. Degradation of the hard phase occurred between 200~400 °C in two stages, resulting from two distinct hard-segment types. Degradation of the soft phase occurred between 400~600 °C and there were also two stages related to the decomposition of PDMS soft segments and macroclics.