EFFECT OF SOFT SEGMENT CHAIN LENGTH ON TAILORING THE PROPERTIES OF ISOCYANATE TERMINATED POLYURETHANE PREPOLYMER, A BASE MATERIAL FOR POLYURETHANE BANDAGE”

Abstract

Isocyanate terminated polyurethane prepolymer, a base material for water curable polyurethane bandage was prepared from diphenylmethane diisocyanate and poly (propylene oxide) glycol. In polyurethanes, the diisocyanate act as hard segment and provides dimensional stability, whereas the polyol which forms the soft segment gives elastomeric character. Due to its segmented structure, polyurethane's with a wide range of physico-mechanical properties can be obtained by varying its monomers types and content. In this paper, the effect of different soft segment length on influencing the structure property relationship of polyurethane prepolymer was studied. The soft segment length was varied by using poly (propylene oxide) glycol having different molecular weight and also by blending two polyols having similar chemical composition but of different molecular weight. The formation of the prepolymer was investigated by Fourier transform infrared spectroscopy (FTIR). The results reveal that with increasing soft segment length, the weight average molecular weight and storage 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 soft segments due to lower isocyanate content. With increasing molecular weight 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 decreases whereas percent elongation increases with increase in soft segment length. The findings of the study will be beneficial for understanding the role played by soft segment length on tailoring the structure and ultimately the properties of isocyanate terminated polyurethane prepolymer.