A method to synthesize low‐molecular‐mass diurethane compounds via reaction between diisocyanates and various primary and secondary alcohols was presented. A number of diurethanes with the melting points below 100oC were revealed. These diurethanes can be used as fusible plasticizers for thermoplastic polyurethanes (TPU) and for high‐filled composites based thereupon. TPU based on oligotetramethyleneoxide diol and on 4,4′‐diphenylmethane diisocyanate and containing 30% of fusible diurethanes were produced. In the presence of such plasticizers, a 3‐order increase in magnitude of the melt flow index was demonstrated. Data evincing significantly larger strength values of TPU and of tungsten‐containing high‐filled composites (94.2 wt %), comparing with thermoplastics plasticized with low‐molecular‐mass liquids, were presented. The mechanism of this phenomenon attributed to the partial crystallization of diurethanes in TPU compositions was described. Samples of low‐toxic thermoplastic polyurethane having density value of 9.4 g/cm3 and meant for protection of various facilities from radioactive radiation, instead of highly toxic metallic, lead, were prepared. Issues of improving the frost resistance of this new type of TPU were considered. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 41481.