Whiskers 9. Synthesis of whisker-like crystals of poly(6-hydroxy-2-naphthoic acid)

Poly(6-hydroxy-2-naphthoic acid), poly(2,6-HNA), was synthesized by three different methods: polycondensation of 6-acetoxy-2-naphthoic acid, or its trimethylsilyl ester, and polycondensation of free 6-hydroxy-2-naphthoic acid with acetic arnhydride in an 'one-pot procedure'. The last method gave whiskers only when a monomer of high purity was used. Different temperatures (350 or 400C) and reaction media tMarlotherm-S, Marlotherm-SCB or Santotherm) were applied. Furthermore, the reaction time and monomer concentration were varied. 6-Acetoxy-2-naphthoic acid yielded whiskers only at concentrations < 0.1 mol I1', whereas its trimethylsilyl ester gave whiskers even at a concentration of 0.4 mol 11. The crystal growth of whisker-like crystals proved to be sensitive to the presence of radical scavengers or acidic transesterification catalysts.