Process for producing molded articles from polylactams by activated anionic polymerization of medium lactams

A homogeneous molded polylauric lactam article free of bubble formations and shrink holes and which does not show a melting point and disintegrates into crumbs when heated to a temperature from approximately 220.degree. C. to 280.degree. C. prepared by a process involving activated anionic polymerization and which comprises:

• (a) adding to a first lactam melt contained in a first vessel at least one polymerization catalyst for the lactam with agitation and maintaining the mixture of the lactam melt and added catalyst under agitation and protected by an inert gas at a first temperature in the range from about 167.5.degree. C. and about 169.5.degree. C., and at a temperature deviation tolerance of about .+-.1.degree. C. for said first temperature;
• (b) adding, following the addition of the catalyst to the first lactam melt, at least one activator for the polymerization of the lactam to a second lactam melt under agitation and maintaining the mixture of the second lactam melt and activator stirred and protected by an inert gas at a second temperature which is lower than the temperature of the first melt and within a temperature range of from about 164.degree. C., and about 166.degree. C., and at a temperature deviation tolerance of about .+-.1.degree. C. for said second temperature;
• (c) pumping the first and second melts at about the melt temperatures by respective first and second gear pumps to a mixing zone through respective first and second essentially straight conveyor tube systems, each respectively at substantially the same temperature as said first and second melts and having an angle of incline to the horizontal plane of a maximum of about 10.degree., each conveyor tube having a volume at least one-third greater than the volume-conveying capacity of the gear pump to which said tube is coupled;
• (d) combining and mixing the melts in a mixing zone maintaining between about 170.degree. C. and about 175.degree. C. to initiate a polymerization reaction;
• (e) injecting the melt from the mixing zone into a mold for the molded article to form the article with attendant release of gas;
• and
• (f) returning at least part of the released gas to at least one of the mixing vessels by the conveyor tube systems.