. "Step (a) is suitably carried out at a temperature from about 50??? C. to about 200??? C., preferably at a temperature of from about 80??? C. to about 150??? C., and more preferably at about 80??? C. to about 120??? C. The temperature to be employed is mainly determined by such factors as activity of the catalytic system and the desired reaction time and boiling points (and decomposition temperatur" . . .