Abstract
Isocyanate terminated polyurethane prepolymer, a ba se material for water curable polyurethane bandage was prepared from diphenylmethane diisocyanate and poly (propylene ox ide) glycol. In polyurethanes, the diisocyanate ac t as hard segment and provides dimensional stability, whereas the polyol which forms the soft segment gives elastomeric char acter. Due to its segmented structure, polyurethane’s with a wide range of phys ico-mechanical properties can be obtained by varyin g its monomers types and content. In this paper, the effect of different soft segment length on influencing the structure prop erty relationship of polyurethane prepolymer was studied. The soft segment length was varied by using poly (propylene oxide) glycol havi ng different molecular weight and also by blending two polyols having similar che mical composition but of different molecular weight . The formation of the prepolymer was investigated by Fourier transform in frared spectroscopy (FTIR). The results reveal that with increasing soft segment length, the weight average molecular weight and sto rage time of the prepolymer increases, whereas the Brookfield viscosity decreases due to higher content of soft segment. The curing time was found higher in prepolymer having longer s oft segments due to lower isocyanate content. With increasing molecular weigh t of the soft segment, the phase separation between the hard and soft segment increases due to which the prepolymer produce low T g. The tensile strength of the polyurethane film dec reases whereas percent elongation increases with increase in soft segment length. The findings of the study will be beneficia l for understanding the role played by soft segment length on tailoring the stru cture and ultimately the properties of isocyanate t erminated polyurethane prepolymer.
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