Chemical product and method

Thermally expandable microspheres having an average particle size from about 1 to about 500 μm and comprising a thermoplastic polymer shell and a propellant entrapped therein, wherein said polymer shell is made of a homo- or co-polymer from ethylenically unsaturated monomers comprising more than 92 wt % nitrile containing monomers and said propellant comprises at least 50 wt % isooctane.

Process for producing thermally expandable microspheres comprising polymerising ethylenically unsaturated monomers in an aqueous suspension in the presence of a propellant to yield microspheres comprising a hollow homo- or co-polymer shell entrapping said propellant wherein said ethylenically unsaturated monomers comprises more than 85 wt % of nitrile containing monomers and said propellant comprises more than 50 wt % of isooctane.

Expandable composition comprising one or more polymeric substances and, as a foaming agent, thermally expandable microspheres comprising a thermoplastic polymer shell and a propellant entrapped therein, wherein said polymer shell is made of a homo- or co-polymer from ethylenically unsaturated monomers comprising more than 85 wt % nitrile containing monomers and said propellant comprises at least 50 wt % isooctane.