High gloss rubber modified monovinylidene aromatic polymers produced by a mass polymerization process

A mass polymerized rubber-modified polymeric composition comprising:

• a continuous matrix phase comprising a polymer of a monovinylidene aromatic monomer, and optionally, an ethylenically unsaturated nitrile monomer, and discrete rubber particles dispersed in said matrix, said rubber particles produced from a rubber component comprising from 5 to 100 weight percent of a functionalized diene rubber having at least one functional group per rubber molecule capable of enabling controlled radical polymerization;
• wherein the composition is further characterized by:
• a) a volume average rubber particle size of from about 0.15 to 0.35 micron,
• b) a total rubber phase volume between 12 and 45 percent, based on the total volume of the combination of the matrix phase and the rubber particles;
• c) a partial rubber phase volume between 2 and 20 percent characterized by rubber particles having a volume average particle size of greater than 0.40 microns;
• and
• d) a crosslinked rubber fraction of at least 85 percent by weight, based on the total weight of the rubber particles.