Polymerization of lactam with graft copolymer promoter

The method which comprises mixing together and copolymerizing to form a solid polyamide

• (a) a major amount of weight of the mixture of at least one lactam monomer and
• (b) a minor amount by weight of the mixture of at least one graft copolymer promoter having a Tg of from about -40.degree. to -100.degree. C. and comprising (I) from about 4 to 13 parts by weight of maleic anhydride grafted on (II) 100 parts by weight of at least one liquid polymer having an average molecular weight of from about 1,000 to 30,000 and being selected from the group consisting of (A) homopolymers, copolymers and mixtures of the same of polymerizable conjugated dienes having from 4 to 6 carbon atoms and (B) copolymers of at least 50% by weight of at least one polymerizable conjugated diene having from 4 to 6 carbon atoms and essentially the balance at least one copolymerizable monomer selected from the group consisting of at least one monovinyl aryl monomer having from 8 to 12 carbon atoms, acrylonitrile and methacrylonitrile and mixtures of the same in admixture with
• (c) an effective catalytic amount of an anionic lactam polymerization catalyst (lactamate salt), the lactam of (a) and (c) having the formula ##STR3## where R is an alkylene radical of from 5 to 11 carbon atoms and R' is hydrogen or an alkyl radical of from 1 to 4 carbon atoms.