Abstract: An extrusion head for the manufacture of tubes including at least one layer of expanded plastic by extruding a stream of molten plastic containing a blowing agent through an annular passage cross section made in the extrusion head. The stream of molten plastic containing the blowing agent spreads out circumferentially and welds itself to itself by the recombining of the two stream fronts. The extrusion head is equipped with a special-purpose thermal regulation device allowing the molten plastic containing the blowing agent to be heated or cooled after the stream fronts have recombined.

Abstract: The invention relates to an extrusion head for the manufacture of tubes comprising at least one layer of expanded plastic by extruding a stream of molten plastic containing a blowing agent through an annular passage cross section made in the extrusion head and in which the stream of molten plastic containing the blowing agent spreads out circumferentially and welds itself to itself by the recombining of the two stream fronts, the said extrusion head being equipped with a special-purpose thermal regulation device allowing the molten plastic containing the blowing agent to be heated or cooled after the stream fronts have recombined.

Abstract: Poly-.epsilon.-caprolactones produced by continuous melt polymerization of .epsilon.-caprolactone with the use of aluminium alkoxides are stabilized for storage by incorporation of an effective quantity of silicon derivative such as, for example, a silicon oxide, an inorganic silicate or a silicon alkoxide, preference being given to silicon alkoxides. This process has the effect of greatly limiting the gradual reduction in the inherent viscosity of the poly-.epsilon.-caprolactones in the course of time. In accordance with a preferred embodiment the incorporation of the silicon derivative is preceded by the incorporation of an effective quantity of water, and this further improves the storage stability of the poly-.epsilon.-caprolactones produced with the use of aluminium alkoxides.

Abstract: Poly-.epsilon.-caprolactones are produced by continuous polymerization of .epsilon.-caprolactone as a melt in an extruder (reactive extrusion) with the use, as polymerization initiator, of aluminium trialkoxides in which at least one alkoxy radical includes at least one other oxygen atom besides the oxygen atom constituting the aluminoxane (AI--O) bond. This oxygen atom is advantageously present in the form of an ester or ether functional group. These initiators are generally in the liquid state at ambient temperature and are furthermore miscible with .epsilon.-caprolactone, with the result that they can be used in the absence of solvent. The appropriate adjustment of the feed flow rates of .epsilon.-caprolactone and of initiator to the extruder permits the manufacture of custom-made poly-.epsilon.-caprolactones which have predesigned weight-average molecular masses.

Abstract: Propylene polymer containing monomer units derived from at least one functional compound (A) comprising at least two vinyl unsaturations and one or a number of aromatic rings which exhibits a structural stress-hardening.