| 摘要 |
Polymer blends with low haze and increased modulus and impact strength are comprised of a styrene butadiene block (SBC) copolymer and at least 62.5 weight percent of a styrene methyl methacrylate copolymer (SMMA). The SBC comprises 30 to 40, preferably 38 weight percent, butadiene. In a first embodiment the SBC comprises at least one tapered block. In a second embodiment, the SBC comprises at least two modes; at least one tapered block where the styrene comprises less than 25 weight percent; first and second charges of styrene with a weight ratio of 1:2 to 2:1; a monoblock formed from the first charge of styrene in the block copolymer preceding the tapered blocks having a molecular weight of 25,000 to 65,000 grams per mole, and the block copolymer having a blocking force of less than 175 pounds. The SMMA contains at least 55 weight percent styrene and no more than 45 weight percent methyl methacrylate. The blends have a haze of less than about 2.0%, a flexural modulus greater than 280000 pounds per square inch, Gardner impact strength of 5 ft-lbs/inch, preferably, greater than about 20 ft-lbs/inch, as measured according to ASTM D5420, and a tensile elongation greater than 20%.
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