Robert F. Harris

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°C in a polyol 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 Mn in the range of 500–700 gmol−1. This is thought to involve a polymerization/precipitation mechanism in which the molecular units are held together by hydrogen bonding into a macrostructure which separates as a stable dispersed phase. This macrostructure has a spiral fibre bundle morphology, a particle size distribution of about 1 to 10 μm, and aspect ratios from about 6 to 20. The urea-terminated poly(1,6-hexamethyleneurea) particles are highly crystalline thermoplastics with a melting point of ∼ 270°C and are only soluble in strong acids, where the macroparticles 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°C. Urea-terminated poly(1,6- hexamethyleneurea) oligomers having a spiral fibre bundle morphology have not been previously reported. These materials are useful as filled polyols for polyurethanes.

Thermal oligomerization of N,N′-(1,6-hexanediyl)bisurea

Abstract N , N ′-(1,6-Hexanediyl)bisurea oligomerizes thermally in the melt (>190°C) to urea-terminated poly(1,6-hexamethyleneurea) with the volatilization of ammonia and isocyanic acid. At higher temperatures (225–250°C) in the liquid phase, the trimerization of isocyanic acid to cyanuric acid also occurs.

Synthesis and characterization of urea-based polyureas: 2. Morphology control in urea-terminated poly(1,6-hexamethyleneurea) particles

Abstract The effects of reaction parameters on the synthesis of urea-terminated poly(1,6-hexamethyleneurea) particles dispersed in a polyol continuous phase have been studied. Oligomeric units are held together by hydrogen bonding into a macrostructure which separates as a stable dispersed phase during synthesis. Monomer addition rate, synthesis temperature and stirring rate are important factors in morphology control of the particles. High aspect ratio (10–20) particles having a spiral fibre bundle morphology (by scanning electron microscopy) are produced at synthesis temperature between 140 and 175°C; spherical particles are produced at 185°C. Particles produced at 140°C have a different crystalline structure from particles produced at higher temperatures. Molecular weight, particle size and the extent of hydrogen bonding increase with increasing synthesis temperature. The structure of these highly crystalline particles is established at an early stage in the reaction. Annealing up to 185°C has little effect on particle morphology. Annealing near the melting point (270°C) results in loss of crystallinity; particle macrostructure is destroyed by melting or dissolution.