Expandable polymeric microspheres, their method of production, and uses and products thereof

Abstract

The present invention is directed to thermo-expandable microspheres and to the expanded microballoons, microcellular foam or foamed composite material that results upon heating the microspheres. The thermo-expandable microsphere of the present invention is characterized by having a polymeric wall surrounding one or more pockets or particles of blowing agent or propellant within the microsphere. The polymeric wall may have reactive functional groups on its surface to give a fusible microsphere. When the microspheres are heated, they expand to form microballoons comprising polymeric shells surrounding one or more internal gaseous voids, and when the microspheres are expanded while in contact with each other, a microcellular foam may be formed. The foam consists of a plurality of microballoons fused together, optionally aided by functional groups present on the surface of the heated microspheres that act to crosslink the material. When microspheres are mixed with a matrix, which can optionally react with functional groups on the microsphere surface, and the resulting combination is heated, the microspheres expand to give a foamed composite material in which the microballoons may be fused or chemically crosslinked to the matrix.

What is claimed is:  
     
         1 . A thermo-expandable plastic microsphere comprising a polymeric wall surrounding one or more pockets of blowing agent within the microsphere, the polymeric wall comprising reactive functionalities.  
     
     
         2 . A thermo-expandable microsphere according to    claim 1    wherein the polymeric wall comprises a polymer selected from the group consisting of anhydride-containing polymers and copolymers, hydroxyl-containing polymers and copolymers, amine-containing polymers and copolymers, naturally occurring polymers, and a mixture of a polymer and one or more reactive oligomers or crosslinkable moieties capable of forming a crosslinked, interpenetrating, or semi-interpenetrating polymeric network within the polymeric wall.  
     
     
         3 . A thermo-expandable microsphere according to    claim 1    wherein the polymeric wall comprises a polymer selected from the group consisting of polystyrene-co-maleic anhydride, polyhydroxyethyl methacrylate, and poly(4-vinyl pyrridine).  
     
     
         4 . A thermo-expandable microsphere according to    claim 2    wherein the naturally occurring polymer is selected from the group consisting of polysaccharides, lipids, and proteins.  
     
     
         5 . A thermo-expandable microsphere according to    claim 2    wherein the naturally occurring polymer is zein.  
     
     
         6 . A thermo-expandable microsphere according to    claim 1    wherein said polymeric wall comprises a polymer having reactive sites within the polymer chain.  
     
     
         7 . A thermo-expandable microsphere according to    claim 1    wherein said polymeric wall further comprises additives selected from the group consisting of crosslinking agents and reactive functional groups incorporated into said wall.  
     
     
         8 . A thermo-expandable microsphere according to    claim 1    wherein said reactive functionalities are polymerizable by free-radical or addition-type polymerization mechanisms.  
     
     
         9 . A thermo-expandable microsphere according to    claim 1   , and said polymeric wall comprising a polymer that is not directly polymerizable by free-radical emulsion or suspension polymerization techniques, and said microsphere being free of residues used to dry microspheres from an aqueous solution.  
     
     
         10 . A thermo-expandable plastic microsphere comprising a polymeric wall surrounding one or more pockets of blowing agent within the microsphere, the polymeric wall comprising a polymer that is not directly polymerizable by free-radical emulsion or suspension polymerization techniques.  
     
     
         11 . A thermo-expandable microsphere according to    claim 10    wherein the polymeric wall comprises a polymer selected from the group consisting of polymer blends, non-random copolymers, block copolymers, branched, comb-shaped, or star-shaped polymers, engineering thermoplastics, naturally occurring polymers, polymers produced by step-growth-type polymerization mechanisms, and a mixture of a polymer and one or more reactive oligomers or crosslinkable moieties capable of forming a crosslinked, interpenetrating, or semi-interpenetrating polymeric network within the polymeric wall.  
     
     
         12 . A thermo-expandable microsphere according to    claim 11    wherein the naturally occurring polymer is selected from the group consisting of polysaccharides, lipids, and proteins.  
     
     
         13 . A thermo-expandable microsphere according to    claim 11    wherein the naturally occurring polymer is zein.  
     
     
         14 . A thermo-expandable microsphere according to    claim 10   , the polymeric wall comprising reactive functionalities.  
     
     
         15 . A thermo-expandable microsphere according to    claim 10   , said microsphere being free of residues used to dry microspheres from an aqueous solution.  
     
     
         16 . A thermo-expandable, plastic microsphere comprising a polymeric wall surrounding one or more pockets of blowing agent within the microsphere, said microsphere being free of residues used to dry microspheres from an aqueous solution.  
     
     
         17 . A thermo-expandable microsphere according to    claim 16    wherein the polymeric wall comprises a polymer selected from the group consisting of thermoplastic polymers, polymer blends, copolymers, block copolymers, branched, comb-shaped, or star-shaped polymers, engineering thermoplastics, naturally occurring polymers, polymers produced by step-growth-type polymerization mechanisms, polymers produced by addition-type polymerization mechanisms, thermosetting polymers, and a mixture of a polymer and one or more reactive oligomers or crosslinkable moieties capable of forming a crosslinked, interpenetrating, or semi-interpenetrating polymeric network within the polymeric wall.  
     
     
         18 . A thermo-expandable microsphere according to    claim 17    wherein the thermoplastic polymer is selected from the group consisting of polystyrene, polystyrene-maleic anhydride, polymethylmethacrylate, polyacrylonitrile, polymethacrylonitrile, polyvinylidene floride, polyvinylidene chloride, polysaccharides, polypeptides, and zein.  
     
     
         19 . A thermo-expandable microsphere according to    claim 16   , the polymeric wall comprising reactive functionalities.  
     
     
         20 . A thermo-expandable microsphere according to    claim 19   , wherein said polymeric wall comprises a polymer selected from the group consisting of styrene-maleic anhydride and zein.