Expandable vinyl aromatic polymers and process for the preparation thereof

Abstract

The present invention is an expandable vinyl aromatic polymer which comprises: a) a matrix of a branched aromatic ionomer, b) 1-10% by weight calculated with respect to the polymer (a), of an expanding agent englobed in the polymeric matrix, c) 0-20% by weight, calculated with respect to the polymer (a), of a filler homogeneously distributed in the polymeric matrix, in which, the branched aromatic ionomer comprises the product of co-polymerizing a first monomer comprising an aromatic moiety and an unsaturated alkyl moiety and a second monomer comprising an ionic moiety and at least two unsaturated moieties, wherein the ionic moiety has at least two ionizable groups, a cationic group that ionizes to form cations and an anionic group that ionizes to form anions, and wherein the cationic group is polyvalent and one capable of forming bridges to other molecules. The present invention also relates to the use of the expandable vinyl aromatic polymer to make expanded articles, in particular insulation boards.

1 . Expandable vinyl aromatic polymer which comprises:
 a) a matrix of a branched aromatic ionomer,   b) 1-10% by weight calculated with respect to the polymer (a), of an expanding agent englobed in the polymeric matrix,   c) 0-20% by weight, calculated with respect to the polymer (a), of a filler homogeneously distributed in the polymeric matrix,   in which,   the branched aromatic ionomer comprises the product of co-polymerizing a first monomer comprising an aromatic moiety and an unsaturated alkyl moiety and a second monomer comprising an ionic moiety and at least two unsaturated moieties, wherein the ionic moiety has at least two ionizable groups, a cationic group that ionizes to form cations and an anionic group that ionizes to form anions, and wherein the cationic group is polyvalent and one capable of forming bridges to other molecules.   
     
     
         2 . Expandable vinyl aromatic polymer according to  claim 1  wherein the first monomer is selected from the group consisting of styrene, alphamethyl styrene, t-butylstyrene, p-methylstyrene, vinyl toluene, and mixtures thereof. 
     
     
         3 . Expandable vinyl aromatic polymer according to  claim 2  wherein the first monomer is styrene. 
     
     
         4 . Expandable vinyl aromatic polymer according to  claim 1  wherein the second monomer is selected from the group consisting of: zinc diacrylate, zinc dimethacrylate, zinc di-vinylacetate, zinc di-ethylfumarate, and the like; copper diacrylate, copper dimethacrylate, copper di-vinylacetate, copper di-ethylfumarate, and the like; aluminum triacrylate, aluminum trimethacrylate, aluminum tri-vinylacetate, aluminum tri-ethylfumarate, and the like; zirconium tetraacrylate, zirconium tetramethacrylate, zirconium tetra-vinylacetate, zirconium tetra-ethylfumarate, and mixtures thereof. 
     
     
         5 . Expandable vinyl aromatic polymer according to  claim 1  wherein the second monomer is zinc diacrylate or zinc dimethacrylate. 
     
     
         6 . Expandable vinyl aromatic polymer according to  claim 1  wherein the branched aromatic ionomer is mixed with up to 50% w of a GPPS. 
     
     
         7 . Expandable vinyl aromatic polymer according to  claim 1  wherein the filler is any material capable to reduce the thermal conductivity of the expanded vinyl aromatic polymer. 
     
     
         8 . Expandable vinyl aromatic polymer according to  claim 1  wherein the filler is selected among: carbon black, graphite, mica, talc, silica, titanium dioxide and barium sulfate. 
     
     
         9 . Expandable vinyl aromatic polymer according to  claim 8  wherein One can cite carbon black with a surface area, measured according to ASTM D-3037/89, ranging from 5 to 200 m2/g. 
     
     
         10 . Process to make the expandable vinyl aromatic polymer according to  claim 1  wherein it is carried out by mixing the branched aromatic ionomer in the melted state with the blowing agent or agents and optionally the fillers. 
     
     
         11 . Process according to  claim 10  wherein the mixing is carried out in a chamber equipped with at least one stirring means and under temperature and pressure conditions which are capable of preventing expansion of the composition, preferably in an extruder, in particular a single-screw or twin-screw extruder, or in one or more static mixers at a temperature greater than the glass transition temperature of the polymer, in particular a temperature ranging from 120 to 250° C. and under an absolute pressure ranging from 0.1 to 10 MPa. 
     
     
         12 . Expandable vinyl aromatic polymer according to  claim 1  wherein it is in the form of beads or granules. 
     
     
         13 . Use of the expandable vinyl aromatic polymer according to  claim 1  to make expanded articles, in particular insulation boards.