SYNTHESIS AND CHARACTERIZATION OF UREA-BASED POLYUREAS .1. UREA-TERMINATED POLY(1.6-HEXAMETHYLENEUREA) POLYOL DISPERSIONS

The reactions of urea with 1,6-hexanediamine at 150 degrees C in a pol yol continuous phase in the presence of a stabilizer for the resultant particles, produce low-molecular-weight oligomers of urea-terminated poly(1,6-hexamethyleneurea) having a M(n) in the range of 500-700 g mo l(-1). This is thought to involve a polymerization/precipitation mecha nism in which the molecular units are held together by hydrogen bondin g into a macrostructure which separates as a stable dispersed phase. T his macrostructure has a spiral fibre bundle morphology, a particle si ze distribution of about 1 to 10 mu m, and aspect ratios from about 6 to 20. The urea-terminated poly(1,6-hexamethyleneurea) particles are h ighly crystalline thermoplastics with a melting point of similar to 27 0 degrees C and are only soluble in strong acids, where the macroparti cles dissociate into their molecular units. High-molecular-weight poly (1,6-hexamethyleneurea) has been synthesized in bulk by other methods and is reported to have a melting point in the range 270-300 degrees C . Urea-terminated poly(1,6-hexamethyleneurea) oligomers having a spira l fibre bundle morphology have not been previously reported. These mat erials are useful as filled polyols for polyurethanes.