Mixing PS(Polystyrene) and PMMA(Poly(methyl methacrylate)) is difficult because PS and PMMA have similar solubility parameters. But using BA(Benzoic Acid) called entropy diluent, polymer blending is perfectly mixed with a simple process. PS and PMMA are dissolved in chloroform and BA. The role of BA is lower the conformational entropy of the polymer chain and interact with hydrogen bonding with PS and PMMA, which leads to the extended of PS and PMMA Chains. The DSC, OM, and IR image experiments show the transformation of PS and PMMA into homogeneous and crystalline polymers by evaporating chloroform and sublimating BA. It also has a dramatic enhancement of the mechanical properties due to crystalline conformation.