Patent GB-918059-A (GB)
Title: Manufacture of expanded polyamides
Inventor: BRUEGGEMANN HORST
IPC: C08J9/04
Filed: 1961-09-26
Abstract: Expanded polyamides are produced by polymerizing a lactam with at least 7 ring members, at temperatures above its melting point and below the melting point of the resultant polyamide, with the aid of an alkaline catalyst in the absence of substances containing or forming hydroxyl groups and in the presence of expanding agents which, under the polymerization conditions, volatilize or decompose with the evolution of gas.  A polymerization activator may also be present in the reaction mixture.  Specified are lactams caprolactam, oenanthic lactam, caprylic lactam, lauric lactam and 4-isopropylcaprolactam and mixtures polymerization catalysts alkali and alkaline earth metals and alkaline-reacting compounds of these metals, e.g. alkali-lactam compounds, potassium hydroxide, potassium carbonate, sodium methylate, sodium amide and calcium oxide and polymerization activators carboxylic acid halides such as benzoyl chloride, esters and anhydrides, isocyanuric and isothiocyanuric acid esters, cyanamides, carbodi-imides and especially substituted ureas, thioureas, guanidines and urethanes. Additives such as kieselguhr and animal charcoal promote the formation of homogeneous, fine cells.  In most of the examples the polymerization activator used is bis-(caprylic lactam-N-carboxylic acid)-hexamethylene diamide.ALSO:Expanded polyamides are produced by polymerizing a lactam with at least 7 ring members, at temperatures above its melting point and below the melting point of the resultant polyamide, with the aid of an alkaline catalyst in the absence of substances containing or forming hydroxyl groups and in the presence of expanding agents which, under the polymerization conditions, volatilise or decompose with the evolution of gas.  A polymerization activator may also be present in the reaction mixture.  Specified are lactams caprolactam, oenanthic lactam, caprylic lactam; lauric lactam and 4- isopropylcaprolactam and mixtures polymerisation catalysts alkali and alkaline earth metals and alkaline-reacting compounds of these metals, e.g. alkalilactam compounds, potassium hydroxide, potassium carbonate, sodium methylate, sodium amide and calcium oxide and polymerization activators carboxylic acid halides such as benzoyl chloride, esters and anhydrides, isocyanuric and isothiocyanuric acid esters, cyanamides, carbodi-imides and especially substituted ureas, thioureas, guanidines and urethanes. Additives such as kieselguhr and animal charcoal promote the formation of homogeneous fine cells.  In most of the examples, the polymerisation activator used is bis- (caprylic lcotam - N - carboxylic acid)-hexamethylene diamide. Specified expanding agents are pentane, hexane, heptane, octane, cyclohexane, benzene, toluene, dibutyl ether, dioxene, azoisobutyronitrile, benzene sulphonic acid hydrazide and aryl sulphazides and mixtures.  The polymerization/expansion may be in a mould, or partial polymerization may be allowed to proceed in an extruder followed by extrusion of the viscous expandable melt through a die into a heated medium to complete the polymerization and effect the expansion.