SYNTHESIS AND CHARACTERIZATION OF UREA-BASED POLYUREAS .2. MORPHOLOGYCONTROL IN UREA-TERMINATED POLY(1,6-HEXAMETHYLENEUREA) PARTICLES

The effects of reaction parameters on the synthesis of urea-terminated poly(1,6-hexamethyleneurea) particles dispersed in a polyol continuou s phase have been studied. Oligomeric units are held together by hydro gen bonding into a macrostructure which separates as a stable disperse d 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 b undle morphology (by scanning electron microscopy) are produced at syn thesis temperature between 140 and 175 degrees C; spherical particles are produced at 185 degrees C. Particles produced at 140 degrees C hav e a different crystalline structure from particles produced at higher temperatures. Molecular weight, particle size and the extent of hydrog en bonding increase with increasing synthesis temperature. The structu re of these highly crystalline particles is established at an early st age in the reaction, Annealing up to 185 degrees C has little effect o n particle morphology. Annealing near the melting point (270 degrees C ) results in loss of crystallinity; particle macrostructure is destroy ed by melting or dissolution.