STRUCTURE CHARACTERIZATION OF POLYURETHANES CONTAINING POLY(DIMETHYLSILOXANE)

The degrees of completion in microphase separation for segmented polyurethanes containing a block segment of poly(ethylene oxide)-b-poly(dimethylsiloxane)-b-poly(ethylene oxide) (PES) were investigated by mechanical and thermal analyses, Fourier transform infrared absorption spectroscopy (FTIR), and small-angle X-ray scattering (SAXS) techniques. These results were compared with those for PES-free polyurethanes having the same molecular weight of the soft segment, M(PTMG), where PTMG is the abbreviation of poly(tetramethylene glycol). The 13 wt % of PES addition lowers the capability of crystallization of the major component of the soft segment, PTMG, and increases the degree of completion in microphase separation. A selective surface enrichment was observed for a blend film of polyurethanes with and without PES by FTIR-attenuated total reflection spectroscopy (ATR). The range of enrichment was on the order of a micron, which is much larger than individual molecular size. SAXS analyses showed that these polyurethanes form a microphase-separated structure. The microdomain structure is well described with the hard-segment domains of 60-70 angstrom long embedded in the soft-segment matrix. The soft-segment chains obey the random-walk statistics in a confined space, which leads to the relation d(s) approximately Z(s)2/3, where d(s) and Z(s) are the domain size and number-average degree of polymerization of the soft-segment chain.