Heterogeneous foam materials

A heterogeneous polymeric foam structure of interconnected open-cells, wherein the foam structure has at least two distinct regions that differ by at least about 20% with regard to one or more of polymer density, polymer composition, surface properties, or microcellular morphology, and wherein the foam is prepared by the process comprising the steps of:

• A) forming a first water-in-oil emulsion from:
• 1) an oil phase comprising:
• a) from about 85 to about 98% by weight of a monomer component capable of forming a copolymer having a Tg of about 95.degree. C. or lower, the monomer component comprising:
• i) from about 20 to about 70% by weight of at least one substantially water-insoluble monofunctional monomer capable of forming an atactic amorphous polymer having a Tg of about 25.degree. C. or lower;
• ii) from about 10 to about 50% by weight of at least one substantially water-insoluble monofunctional comonomer capable of imparting toughness about equivalent to that provided by styrene;
• iii) from about 5 to about 50% by weight of a first substantially water-insoluble, polyfunctional crosslinking agent selected from divinylbenzenes, trivinylbenzenes, divinyltoluenes, divinylxylenes, divinylnaphthalenes divinylalkylbenzenes, divinylphenanthrenes, divinylbiphenyls, divinyldiphenylmethanes, divinylbenzyls, divinylphenylethers, divinyldiphenylsulfides, divinylfurans, divinylsulfide, divinylsulfone, and mixtures thereof;
• and
• iv) from 0 to about 15% by weight of a second substantially water-insoluble, polyfunctional crosslinking agent selected from polyfunctional acrylates, methacrylates, acrylamides, methacryl-amides, and mixtures thereof;
• and
• b) from about 2 to about 15% by weight of an emulsifier component which is soluble in the oil phase and which is capable of forming a stable water-in-oil emulsion, the emulsifier component comprising a primary emulsifier having at least about 40% by weight emulsifying components selected from diglycerol monoesters of branched C.sub.16 -C.sub.24 fatty acids, linear unsaturated C.sub.16 -C.sub.22 fatty acids, and linear saturated C.sub.12 -C.sub.4 fatty acids;
• sorbitan monoesters of branched C.sub.16 -C.sub.24 fatty acids, linear unsaturated C.sub.16 -C.sub.22 fatty acids, linear saturated C.sub.12 -C.sub.14 fatty acids;
• diglycerol monoaliphatic ethers of branched C.sub.16 -C.sub.24 alcohols, linear unsaturated C.sub.16 -C.sub.22 alcohols, and linear saturated C.sub.12 -C.sub.14 alcohols, and mixtures thereof;
• and
• 2) a water phase comprising an aqueous solution containing:
• (a) from about 0.2 to about 20% by weight of a water-soluble electrolyte;
• and (b) an effective amount of a polymerization initiator;
• 3) a volume to weight ratio of water phase to oil phase in the range of from about 20:1 to about 200:1;
• B) optionally forming a second, distinct water-in-oil emulsion which is different in at least one respect from the first emulsion;
• and
• C) either p2 1) a) combining the first and second water-in-oil emulsions in a forming vessel prior to polymerizing the monomer components in the oil phase of either of the water-in-oil emulsions;
• and
• b) polymerizing both emulsions to form a polymeric, heterogeneous foam;
• 2) a) partly or completely polymerizing the monomer components in the oil phase of the first water-in-oil emulsion;
• b) combining the material from step C)2)a) and the second water-in-oil emulsion;
• and
• c) polymerizing the second emulsion, and the first emulsion if combined when partly cured, to provide a polymeric, heterogeneous foam;
• or
• 3) making only the first water-in-oil emulsion while varying the process conditions by which it is formed in a controlled fashion, either rhythmically or continuously, using a single emulsion forming head, to form a heterogeneous foam.