Abstract: Seeding a melt of pentaerythritol tetrakis-[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] with a small amount of the crystalline .beta.-, .delta.- or .lambda.-modification of this compound in an extruder, kneader or internal mixer at 70.degree.-130.degree. C. gives, within a few minutes, pure crystalline product without the use of a hitherto mandatory and environmentally undesirable solvent.Also described is a novel crystalline thermostable .lambda.-modification of pentaerythritol tetrakis-[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate].

Abstract: A process for foaming thermoplastic materials by adding to the plastics material 0.05 to 5 percent by weight of a dioxazolone of the formula I ##STR1## in which n is 1, 2 or 3, and when n is 1R is C.sub.1 -C.sub.12 -alkyl, C.sub.2 -C.sub.12 -alkenyl, C.sub.7 -C.sub.9 -aralkyl, C.sub.3 -C.sub.6 -cycloalkyl, C.sub.6 -C.sub.10 -aryl, or phenyl substituted by C.sub.1 -C.sub.9 -alkyl, halogen, C.sub.1 -C.sub.9 -alkoxy or nitro, or it is a heterocyclic radical, or when n is 2R is C.sub.1 -C.sub.8 -alkylene, ethenylene, m- or p-phenylene, m- or p-halophenylene, biphenylene, oxy-bis-(p-phenylene), 2,5-thienylene, 2,5-furylene, 2,6-pyridylene or naphthylene, or when n is 3R is phenenyl,and subsequently heating the mixture.

Abstract: Tris-tetrazoles of formula I, ##STR1## wherein A is alkylene and R is hydrogen, alkyl or phenyl, are suitable blowing agents for thermoplastic resins, especially for polycarbonates and aromatic polyethers. The foaming process can be carried out at a temperature range of 230.degree. to 300.degree. C., the resulting foamed articles have a fine and homogeneous cellular structure.The tris-tetrazoles I can be synthesized from the corresponding tris-nitriles or tris-imidchlorides by reaction with an alkali azide.

Abstract: Tris-tetrazoles of formula I, ##STR1## wherein A is alkylene and R is hydrogen, alkyl or phenyl, are suitable blowing agents for thermoplastic resins, especially for polycarbonates and aromatic polyethers. The foaming process can be carried out at a temperature range of 230 to 300.degree. C, the resulting foamed articles have a fine and homogenous cellular structure.The tris-tetrazoles I can be sythesized from the corresponding tris-nitriles or tris-imidchlorides by reaction with an alkali azide.