POLYMERIC NANOFOAM

A polymeric nanofoam has a continuous polymer phase containing at least one (meth)acrylic-free acrylonitrile-containing copolymer and at least one (meth)acrylic polymer where the concentration of (meth)acrylic polymer is in a range of 5-90 weight-percent of the total continuous polymer phase while the amount of methacrylic copolymer is 50 weight-percent or less of the total continuous polymer phase; the polymeric foam having a porosity of at least 50%, an absence of nano-sized nucleating additives and at least one of the following: (a) a number average cell size of 500 nanometers or less; and (b) an effective nucleation site density of at least 1×1014 sites per cubic centimeter of prefoamed material. The total weight of copolymerized acrylonitrile is in a range of 3-28 weight-percent based on total continuous polymer phase weight. At least one (meth)acrylic-free acrylonitrile-containing copolymer has a higher glass transition temperature than all of the (meth)acrylic polymers.