Homogeneous molded article produced from polylactam by activated anionic polymerization of medium lactams

A homogenous molded polylactam article formed of a lactam containing 13 to 15 carbon atoms in the lactam ring which are free of bubble formations and shrink holes and which does not show a melting point and crumbles after hardening 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 melt of the lactam 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 inery 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 melt of the lactam, at least one activator for the polymerization of the lactam to a second melt of the lactam under agitation and maintaining the mixture of the second melt of the lactam and activator stirred and protected by an inert gas at a second temperature which is lower than the temperature of the first mel 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 melt and second melt 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 maintained between about 170.degree. C. and about 175.degree. C. to initiate a polumerization 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.