Positive skew styrene-acrylonitrile copolymer foam

1. A polymeric foam comprising a thermoplastic polymer composition having cells defined therein, wherein 75 or more percent by weight of all non-halogenated polymers in the polymeric foam is a styrene-acrylonitrile copolymer composition having a polymerized acrylonitrile content distribution with a positive skew, a positive percent difference between the mean and the median copolymerized AN content distribution, and a mean copolymerized AN content of 20 weight-percent or less.

2. The polymeric foam of claim 1 , wherein the styrene-acrylonitrile copolymer composition comprises 0.5 weight-percent or less, based on total styrene-acrylonitrile copolymer composition weight, of styrene-acrylonitrile copolymers having an copolymerized acrylonitrile content of more than 30 weight-percent.

3. The polymeric foam of claim 1 , wherein the styrene-acrylonitrile copolymer composition accounts for 95 percent by weight or more of all non-halogenated polymers in the thermoplastic polymer composition.

4. The polymeric foam of claim 1 , further characterized by having less than 30% open-cell content and a density of 64 kilograms per cubic meter or less.

5. The polymeric foam of claim 4 , further characterized by having an average vertical cell size of 0.15 millimeters or more and 0.35 millimeters or less.

6. The polymeric foam of claim 1 , wherein the polymeric foam has at least one surface and 80% or more of any 200 square centimeters portion of the surface that is centered on the foam's surface and extending to 80% of the foam's surface dimensions is free of visible defects.

7. A process for producing a polymeric foam comprising the following steps:

a. Providing a foamable polymer composition at a mixing temperature and a mixing pressure, the foamable polymer composition comprising a thermoplastic polymer composition and a blowing agent that comprises water; and

b. Exposing the foamable polymer composition to a pressure lower than the mixing pressure and allowing it to expand into a polymeric foam;

wherein 75 percent or more by weight of all non-halogenated polymers in the foamable polymer composition is a styrene-acrylonitrile copolymer composition having a polymerized acrylonitrile content distribution with a positive skew in AN content distribution, a positive percent difference between the mean and the median copolymerized AN content distribution, and a mean copolymerized AN content of 20 weight-percent or less.

8. The process of claim 7 , wherein the styrene-acrylonitrile copolymer composition comprises 0.5 weight-percent or less, based on total styrene-acrylonitrile copolymer composition weight, of styrene-acrylonitrile copolymers having an copolymerized acrylonitrile content of more than 30 weight-percent.

9. The process of claim 7 , wherein the process is an extruded foam process and step (b) comprises expelling the foamable polymer composition through a die into a lower pressure than the mixing pressure and wherein the die has a die lip temperature that is 100 degrees Celsius or higher.

10. The process of claim 9 , wherein the polymeric foam has at least one primary surface and a width and is further characterized by 80% or more of any 200 square-centimeter portion of any primary surface of the foam that is centered on the foam's primary surface and extending to 80% of the foam's width being free of visible defects.

11. The process of claim 9 , wherein the die lip temperature is 110 degrees Celsius or higher.

12. The process of claim 7 , wherein the styrene-acrylonitrile copolymer composition accounts for 95 percent by weight or more of all non-halogenated polymers in the polymeric foam.

13. The process of claim 7 , wherein the polymer foam is further characterized by having less than 30% open-cell content and a density of 64 kilograms per cubic meter or less.

14. The process of claim 13 , wherein the polymer foam is further characterized by having an average vertical cell size of 0.15 millimeters or more and 0.35 millimeters or less.

15. The process of claim 7 , wherein the polymeric foam has at least one primary surface and a width and further characterized by 80% or more of any 200 square-centimeter portion of any primary surface of the foam that is centered on the foam's primary surface and that extends to 80% of the foam's width being free of visible defects.