PROCESS FOR PREPARING HIGH MOLECULAR WEIGHT POLYALKYLENE TEREPHTHALATES BY INTIMATELY MIXING A MOLTEN STREAM OF LOW MOLECULAR WEIGHT POLYALKYLENE TEREPHTHALATE WITH A MELT OF HIGHER MOLECULAR WEIGHT POLYALKYLENE TEREPHTHALATE

摘要

PICT:1112682/C3/1 A continuous process for making a high molecular weight poly(glycol terephthalate) of specific viscosity 0.40 to 2.0 comprises conveying a continuous stream of molten poly (glycol terephthalate) having specific viscosity 0.2 to 0.85 into a vigorously agitated melt of a poly-(glycol terephthalate) of higher molecular weight, rapidly and completely mixing the two materials and maintaining them at 260-310 DEG C. under reduced pressure and in the presence of a polycondensation catalyst for an average residence time of 10 minutes to 15 hours. The difference between the specific viscosities of the two poly(glycol terephthalates) is at least 0.2. The glycol is preferably ethylene glycol, a propylene glycol, a butane diol, p-xylylene glycol, a cyclobutanediol or 1:4-dimethylol cyclohexane. Part of the terephthalic acid may be replaced by another dicarboxylic acid. In the examples, low molecular weight polyethylene terephthalate is metered via an inlet 6 into a condensation reactor comprising an external hollow screw 1 which presses the melt downwardly until it is conveyed through bore-holes 2 into the interior of the screw where it is conveyed upwardly by a stationary screw 3. At the upper end of the screw 3, the melt leaves the interior of the screw 1 through bore-holes 4 and is again conveyed downwardly whereby the melt is continuously circulated. Glycol vapours released are withdrawn via outlet 8 whilst high molecular weight poly(glycol terephthalate) is withdrawn via outlet 7.