and the tube again is evacuated and filled with nitrogen 2x the contents of the tube again stirred under nitrogen are heated at 283 u00b0 c for about 21 4 hours the distillate by product is collected the nitrogen flow is halted and the system placed under reduced pressure reaches 2 0 mm hg in about 5 min after being heated 283 u00b0 c and stirred under vacuum 2 0 0 3 mm hg for about 1 hour the reaction system becomes unstirrable the reactants are cooled briefly after which the temperature is then raised to 305 u00b0 c in a few minutes whereupon the stirring is again accomplished pressure is 0 25 mm hg these conditions are maintained for another 25 minutes after which the reaction system again solidifies and becomes unstirrable heating and reduced pressure 0 25 1 8 mm hg are maintained for another 85 minutes after which the system is allowed to cool and the product is isolated the yield is 16 0 g the copolymer flows at 338 u00b0 c and exhibits optical anisotropy above that temperature tot a plug of this copolymer is spun through a 1 hole spinneret hole diameter 0 023 cm at 349 u00b0 c filament wind up speed is 549 m.