PROCEDIMENTO IN CONTINUO PER LA RIDUZIONE DEL PESO MOLECOLARE DI COPOLIMERI E TERPOLIMERI DELL'ETILENE

Continuous process for reducing the molecular weight of ethylene copolymers and terpolymers [EP(D)M)] comprising the following stages: (a) providing at least one single screw extruder comprising a chamber, a reciprocating single screw mounted in said chamber, said reciprocating single screw being capable of rotating and oscillating within said chamber, said chamber having at least one feeding opening and at least one discharging opening, said extruder comprising three conveying and mixing zones, a gear pump, an underwater die-face cutter; (b) feeding at least one ethylene copolymer or terpolymer [EP(D)M)] into said single screw extruder; (c) conveying said at least one ethylene copolymer or terpolymer [EP(D)M)] through a first conveying and mixing zone which operates at a temperature comprised between 140°C and 260°C, preferably comprised between 150°C and 250°C, wherein said ethylene copolymer or terpolymer [EP(D)M)] is uniformly mixed and heated and uniformly softened; (d) conveying said at least one uniformly softened ethylene copolymer or terpolymer [EP(D)M)] leaving said first conveying and mixing zone to a second conveying and mixing zone which operates at a temperature comprised between 220°C and 330°C, preferably comprised between 230°C and 320°C, wherein said ethylene copolymer or terpolymer [EP(D)M)] is further mixed and heated and partially degraded; (e) conveying said at least one partially degraded ethylene copolymer or terpolymer [EP(D)M)] leaving said second conveying and mixing zone to a third conveying and mixing zone which operates at a temperature comprised between 170°C and 340°C, preferably comprised between 180°C and 330°C, wherein said ethylene copolymer or terpolymer [EP(D)M)] is further mixed and heated and further degraded; (f) conveying said at least one further degraded ethylene copolymer or terpolymer [EP(D)M)] leaving said third conveying and mixing zone to said gear pump which operates at a temperature comprised between 170°C and 340°C°C, preferably comprised between 180°C and 330°C, wherein said ethylene copolymer or terpolymer [EP(D)M)] is further degraded; (g) recovering said at least one further degraded ethylene copolymer or terpolymer [EP(D)M)] leaving said underwater die-face cutter. The ethylene copolymers and terpolymers [EP(D)M] obtained by the above process are advantageously usable as viscosity index improvers (V.I.I.) of lubricating oils.