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# ps_3 - consists of 10 g of pure homopolymer PS(Mw=50,000...

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Problem Set 3 E-344 Due: Thursday, 8 June, 2006 Summer 2006 at the beginning of lecture Core 5.9 Polypropylene Callister 14.9 polymer molecule size Callister 14.13 compare thermoplastics and thermosets Callister 14.15a PE-PP alternating copolymer Callister 14.23a and 14.23b crystallization Callister 15.21 c, d, e Callister 15.29 Materials selection for an ice cube tray Callister 15.38 Nylon 6,6 Problem 5.xx Assuming all of the sulfur is consumed during the process, what mass of sulfur must be added to 100 g of polybutadiene homopolymer in order to crosslink 3% of the possible crosslinking sites? How would the properties of this rubber compare to an identical sample which has 10% of its possible sites crosslinked? Problem 5.xy Polybutadiene (PB) and polystyrene (PS) are immiscible polymers. In other words, they do not like to mix but instead phase separate whenever possible. Suppose two specimens are heated to a temperature 200 o C where both PS and PB are molten. One specimen
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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 μ 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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