Expandable granulates based on vinyl-aromatic polymers having an improved expandability and process for the preparation thereof

Expandable granulates, having compositions based on vinyl-aromatic polymers, comprising:

• a) 65-99.8% by weight of a copolymer obtained by polymerizing 85-100% by weight of one or more vinyl-aromatic monomers having general formula (I) and 0-15% by weight of an α-alkylstyrene in which the alkyl group contains from 1 to 4 carbon atoms,
• wherein in general formula (I), n is zero or an integer ranging from 1 to 5, and Y is a halogen or an alkyl or alkoxyl radical having from 1 to 4 carbon atoms;
• b) 0.01-20% by weight, calculated with respect to the polymer (a), of a carbon black having an average diameter ranging from 10 to 1000 nm and a surface area ranging from 5 to 200 m2/g;
• c) 0.01-5% by weight, calculated with respect to the polymer (a), of
• c1 oxides and sulfates and lamellar dichalcogenides of metals of groups IIA, IIIA, IIIB, IVB, VIB or VIIIB;
• or
• c2) oxides and sulfates of metals of groups IIA, IIIA, IIIB, IVB, VIB or VIIIB, or
• c3) lamellar dichalcogenides of metals of groups IIA, IIIA, IIIB, IVB, VIB or VIIIB;
• or
• c4) oxides of metals of groups IIA, IIB, VIB or VIIIB;
• or
• c5) sulfates and lamellar dichalcogenides of metals of groups IIA, IIIA, IIIB, IVB, VIB or VIIIB;
• or
• c6) sulfates of metals of groups IIA selected from Mg and Ba, IIIA, IIIB, IVB, VIB or VIIIB;
• d) at least one of the following additives d1) and d2):
• d1) 0.01-5% by weight, calculated with respect to the polymer (a), of graphite having an average diameter ranging from 0.5 to 50 μm;
• d2) 0.01-5% by weight, calculated with respect to the polymer (a), of inorganic derivatives of silicon of the lamellar type;
• e) 0-5% by weight, calculated with respect to the polymer (a), of a nucleating agent;
• and
• f) 1-6% by weight, calculated with respect to 100 parts of the total of (a)-(e), of one or more expanding agents.