Process for the preparation of expandable vinyl aromatic polymers with a reduced thermal conductivity by polymerization in suspension

1. A process for preparing a bead of a flame-retardant expandable vinyl aromatic polymer, the process comprising:

polymerizing a vinyl aromatic monomer in aqueous suspension, and

adding an expanding agent before, during, or after the polymerizing,

wherein the process is carried out with a system consisting of water the vinyl aromatic monomer, a peroxide initiator, an amide, a flame-retardant, and optionally the expanding agent;

wherein the amide has formula (I):

R 1 CONHCH 2 —CH 2 NHCOR 2   (I);

wherein R 1 and R 2 are each independently an (iso)alkyl radical CH 3 (CH 2 ) n , a C 6 -C 12 aromatic radical, or a C 7 -C 25 alkylaromatic radical; if either or both of R 1 and R 2 is an (iso)alkyl radical CH 3 (CH 2 ) n , each n is independently from 10 to 20;

wherein the flame-retardant is a brominated additive optionally with a synergic agent comprising a C—C or C—O—O—C thermolabile bond, wherein the brominated additive has a bromine content higher than 30% by weight;

wherein the bead is capable of producing an expanded article with a reduced thermal conductivity; and

wherein the peroxide initiator is active at a temperature higher than 80° C.

2. The process of claim 1 , wherein a content of the amide is 5 to 5,000 ppm, with respect to a weight of the vinyl aromatic monomer.

3. The process of claim 1 , wherein the amide is N,N′-ethylene-bis-stearamide.

4. The process of claim 1 , wherein the expanding agent is at least one expanding agent selected from the group consisting of an aliphatic or cyclo-aliphatic hydrocarbon having from 3 to 6 carbon atoms; a halogenated derivative of an aliphatic hydrocarbon having from 1 to 3 carbon atoms; carbon dioxide; and ethyl alcohol.

5. The process of claim 1 , wherein a content of the expanding agent is from 1 to 10% by weight, with respect to a weight of the vinyl aromatic monomer.

6. The process of claim 1 , wherein the flame-retardant is an aliphatic, cyclo-aliphatic, brominated aromatic compound with a bromine content higher than 30% by weight.

7. The process of claim 1 , wherein a content of the flame-retardant is from 0.1 to 3% by weight, with respect to a weight of the vinyl aromatic monomer.

8. The process of claim 1 , wherein the flame-retardant is the brominated additive with the synergic agent comprising a C—C or C—O—O—C thermolabile bond.

9. The process of claim 8 , wherein a content of the synergic agent is from 0.01% to 1% by weight, with respect to a weight of the vinyl aromatic monomer.

10. The process of claim 1 , wherein the vinyl aromatic monomer is styrene or a mixture of styrene comprising up to 25% by weight of α-methylstyrene.

11. The process of claim 1 , wherein, in formula (I):

R 1 , R 2 , or both are an (iso)alkyl radical CH 3 (CH 2 ) n , and

each n is independently from 16 to 18.

12. The process of claim 1 , wherein the bead is capable of producing an expanded article with a density of from 5 to 50 g/L and a thermal conductivity of from 25 to 50 mW/mK.

13. The process of claim 2 , wherein the content of the amide is from 10 to 500 ppm, with respect to a weight of the vinyl aromatic monomer.

14. The process of claim 1 , wherein the vinyl aromatic monomer comprises a monomer of formula (II):

wherein

R is hydrogen or a methyl group,

n is an integer of from zero to 5, and

each Y, if Y is present, is independently a halogen or an alkyl or alkoxyl radical having from 1 to 4 carbon atoms.

15. The process of claim 1 , wherein adding the expanding agent is during the polymerizing.

16. A process for preparing a bead of a flame-retardant expandable vinyl aromatic polymer, the process comprising:

polymerizing a vinyl aromatic monomer in aqueous suspension, and

adding an expanding agent before, during, or after the polymerizing,

wherein the process is carried out with a system consisting of water, the vinyl aromatic monomer, a peroxide initiator, an amide, a flame-retardant, and optionally the expanding agent;

wherein the amide has formula (I):

R 1 CONHCH 2 —CH 2 NHCOR 2   (I);

wherein R 1 and R 2 are each independently an (iso)alkyl radical CH 3 (CH 2 ) n , a C 6 -C 12 aromatic radical, or a C 7 -C 25 alkylaromatic radical; if either or both of R 1 and R 2 is an (iso)alkyl radical CH 3 (CH 2 ) n , each n is independently from 10 to 20;

wherein the flame-retardant is a brominated additive with a synergic agent comprising a C—C or C—O—O—C thermolabile bond, wherein the brominated additive has a bromine content higher than 30% by weight;

wherein the bead is capable of producing an expanded article with a reduced thermal conductivity; and

wherein the peroxide initiator is active at a temperature higher than 80° C.