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Unformatted text preview: consists of 10 g of pure homopolymer PS (Mw=50,000 g/mole) mixed with 10 g of PB (Mw=50,000 g/mole). The other specimen consists of 20 g of a PS-PB diblock copolymer where the PS block is 50 wt% of each diblock molecule. When these specimens are cooled to room temperature, how might the spatial distribution of PS-rich and PB-rich phases differ? Briefly explain your logic. Problem 5.xz Rubber cement is a typically a mixture of polyisoprene, or a similar rubber, with one or more small-molecule organic solvents such as heptane, a high vapor pressure liquid which is immiscible with water (see adjacent diagram). Suppose 200 l of a 1 wt% solution of polyisoprene (Mw=20 kg/mole) dissolved in heptane is spread over a square surface 1 cm x 1 cm in size for use as an adhesive. Estimate the thickness of the solid rubber film after the hepane solvent evaporates. Comment on why heptane is a good solvent for polyisoprene whereas water is not. Scan multiple choice review questions and practice on many of them....
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- Spring '09