Effect of Hard Segments on Morphology and Properties of Thermoplastic Polyurethanes

Abstract

A series of thermoplastic polyurethanes was synthesized with varying hard segment composition or content and the effect of the hard segments on morphology and properties was studied by differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), thermal mechanical analysis (TMA), Fourier transform infrared analysis (FTIR) and tensile testing. The diisocyanates included 4,4' -diphenylmethane diisocyanate (MDI) and 4,4' -dicyclohexylmethane diisocyanates (H,₂MDI). The chain extenders 1,4-butanediol, 1,5-pentanediol and 1,3-butanediol were used. The soft segment material was poly(oxytetramethylene) glycol of molecular weight 2000. It was found that the interchain attractive forces between hard segments affect physical properties and morphologies. The degree of phase mixing, hardness and strength increased with increasing hard segment content and with decreasing degree of hard segment crystallinity (packing arrangements) at the same hard segment content.