Structure and Properties of Segmented Block Copolymer(II) -Effect of Hard Segment Content on the Thermal Stability of Polyurethanes-

Segmented Block Copolymer의 구조 및 특성(II) -Hard Segment 함량이 Polyurethane의 열 안정성에 미치는 영향-

Polyurethane (PU) containing various amounts of hard segment (HS) were synthesized with MDI, BD and PTMO of 1800 g/mol molecular weight. Effects of HS content on the thermal stability of polyurethanes were studied with DSC, FTIR and SAXS methods. Depending on the HS content in polyurethanes, number of and temperature of the endothermic transition varied. The other-disorder-transition (ODT) was also observed through the thermally induced changes of the absorbance of the hydrogen-bonded carbonyl stretching band in infrared spectrum. The temperatures at which the abrupt decreases in absorbance of hydrogen-bonded carbonyl stretching band occurred coincided well with the temperatures of endothermic transition in DSC thermograms. From the SAXS profiles obtained during a heating process, the parameters such as invariant (Q), interfacial thickness (E) and Porod constant ($K_{p}$) were calculated assuming the linearly-changing electron density function in the interfacial region. With the ODT in the region I and II, an abrupt decrease of Q, increase of E and $K_{p}$ have been confirmed. The $T_{ODT}$ in region II obtained with three different methods was fairly consistent indicating close correlation between the three methods. The schematic model for the internal structure of PU's containing different amounts of HS suggested in the previous study was found to be useful in interpreting the effect amounts of HS suggested in the previous study was found to be useful in interpreting the effect of HS content on the thermal stability of PU characterized in this work.