The present invention relates to thermally expandable thermoplastic microspheres comprising a polymer shell made from ethylenically unsaturated monomers encapsulating a propellant, said ethylenically unsaturated monomers comprising from 21 to 80 wt % of methacrylamide and from 20 to 70 wt % methacrylonitrile, the total amount of methacrylamide and methacrylonitrile being from 70 to 100 wt % of the ethylenically unsaturated monomers. Furthermore, the invention relates to production and use of such microspheres.
1. Thermally expandable thermoplastic microspheres comprising a polymer shell formed by a reaction product of ethylenically unsaturated monomers encapsulating a propellant, said ethylenically unsaturated monomers comprising from 31 to 80 wt % of methacrylamide and from 20 to 70 wt % methacrylonitrile, the total amount of methacrylamide and methacrylonitrile being from 70 to 100 wt % of the ethylenically unsaturated monomers.
2. The microspheres of claim 1 , wherein said ethylenically unsaturated monomers comprise from 30 to 60 wt % of methacrylonitrile.
3. The microspheres of claim 1 , wherein the total amount of methacrylamide and methacrylonitrile is from 80 to 100 wt % of the ethylenically unsaturated monomers.
4. The microspheres of claim 3 , wherein the total amount of methacrylamide and methacrylonitrile is from 90 to 100% of the ethylenically unsaturated monomers.
5. The microspheres of claim 1 , wherein said ethylenically unsaturated monomers comprise from 40 to 60 wt % of methacrylamide.
6. The microspheres of claim 1 , wherein said ethylenically unsaturated monomers comprise from 40 to 60 wt % of methacrylonitrile.
7. The microspheres of claim 1 , wherein said ethylenically unsaturated monomers comprise less than 10 wt % of carboxylic acid containing monomers.
8. The microspheres of claim 1 , wherein said propellant comprises a hydrocarbon selected from the group consisting of isobutane, isopentane, isohexane, cyclohexane, isooctane, isododecane, and mixtures thereof, preferably isooctane.
9. The microspheres of claim 8 , wherein said propellant comprises from 50 to 100 wt % of isooctane.
10. A process for the production of the thermally expandable microspheres of claim 1 , comprising the steps of polymerising ethylenically unsaturated monomers in the presence of a propellant to yield microspheres comprising a polymer shell encapsulating said propellant, said ethylenically unsaturated monomers comprising from 31 to 80 wt % of methacrylamide and from 20 to 70 wt % methacrylonitrile, the total amount of methacrylamide and methacrylonitrile being from 70 to 100 wt % of the ethylenically unsaturated monomers.
11. Expanded microspheres prepared by a process comprising the step of expanding the expandable microspheres of claim 1 .
12. An expandable formulation comprising a thermoplastic polymer matrix and the expandable microspheres of claim 1 .
13. A foaming agent comprising the thermally expandable microspheres of claim 1 .
14. A method of molding polymeric materials comprising the step of combining the thermally expandable microspheres of claim 1 with a molding material.
15. The microspheres of claim 1 , wherein said ethylenically unsaturated monomers are free from carboxylic acid containing monomers.
16. The foaming agent of claim 13 comprising an expandable formulation including a thermoplastic polymer matrix and the thermally expandable microsphere.
17. The method of claim 14 comprising an expandable formulation including a thermoplastic matrix and the thermally expandable microsphere.