The Effect of Chain Extender on Dynamic Viscoelastic Properties of Segmented Polyurethanes

Polyether-urea segmented Polyurethanes with systematically varying blockness of hard segment were prepared by a prepolymer technique by using different (NCO)/(OH) ratio and diamines of different methylene sequences for chain extenders. The employed diamines are hydrazine (HD), ethylenediamine (EDA), tetramethylenediamine (TMDA), and hexamethylenediamine (HMDA). Dynamic viscoelastic properties of segmented polyurethanes were investigated at 110 Hz in the temperature range of -150 to 150℃. Infrared spectroscopy, differential scanning calorimetry, and wide-angle X-ray diffraction were also studied in order to obtain knowledges about hydrogen bonding, the extent of domain formation, and paracrystalline structure in segmented polyurethanes. With increasing methylene group sequence in chain extenders, the frequencies assigned to hydrogenbonded C=O stretching vibration of urea linkage sifted from 1665 to 1625 cm-1 and its intensity increased. In wide-angle X-ray diffraction, the diffraction pattern at about 10Å became sharper with increasing (NCO)/(OH), that is the blockness of hardsegment, suggesting that some short range ordering of this dimension is caused by hard segmnts. The weak diffractions at 3.83 Å and 5.06 Å appearing in EDA, TMDA, HMDA series, which is originated from the introduction of methylene sequences showed the same trend. DSC results revealed the crystallization of soft polyether segment. In PTMG 1000 series, as the hard segment content was increased, main dispersion peak of tanδ shifted to higher temperatures, decreased in its height, and broadened. In PTMG 2000 series, however, the height of tanδ peak increased. By the introduction of methylene sequences in chain extender, main dispersion of tanδ shifted to a litt1e lower temperature and its height of peak was in the order of HD >HMDA> TMDA in PTMG 1000K = 2.0 series, but was HMDA>EDA> HD in K=3.0 series. In PTMG 2000 K=2.0 series, main dispersion was a broad one and shifted to higher temperature, and its height was in the order of HD > TMDA > EDA, but in K=3.0 series HD > TMDA ～ EDA ～ HMDA. The properties of the segmented polyurethanes were discussed and explained in terms of the variety of paracrystalline structure developed from the domain formation of hard segment and the crystallization of soft polyether segment