MSE 104 HW #4 Nov 28 – Dec 5, 2012 14.17 Calculate the number-average molecular weight of a random nitrile rubber [poly(acrylonitrilebutadiene) copolymer] in which the fraction of butadiene repeat units is 0.30; assume that this concentration corresponds to a degree of polymerization of 2000. 14.19 (a) Determine the ratio of butadiene to styrene repeat units in a copolymer having a numberaverage molecular weight of 350,000 g/mol and degree of polymerization of 4425. (b) Which type(s) of copolymer(s) will this copolymer be, considering the following possibilities: random, alternating, graft, and block? Why? 14.23 For each of the following pairs of polymers, do the following: (1) state whether it is possible to determine whether one polymer is more likely to crystallize than the other; (2) if it is possible, note which is the more likely and then cite reason(s) for your choice; and (3) if it is not possible to decide, then state why. (a) Linear and syndiotactic poly(vinyl chloride); linear and isotactic polystyrene (b) Network phenol-formaldehyde; linear and heavily crosslinked cis-isoprene (c) Linear polyethylene; lightly branched isotactic polypropylene (d) Alternating poly(styrene-ethylene) copolymer; random poly(vinyl chloride-tetrafluoroethylene) copolymer 15.20 For each of the following pairs of polymers, do the following: (1) state whether it is possible to decide whether one polymer has a higher tensile strength than the other; (2) if this is possible, note which has the higher tensile strength and then cite the reason(s) for your choice; and (3) if it is not possible to decide, then state why. (a) Syndiotactic polystyrene having a number-average molecular weight of 600,000 g/mol; atactic polystyrene having a number-average molecular weight of 500,000 g/mol (b) Random acrylonitrile-butadiene copolymer with 10% of possible sites crosslinked; block acrylonitrile-butadiene copolymer with 5% of possible sites crosslinked. (c) Network polyester; lightly branched polypropylene 15.22 For each of the following pairs of polymers, plot and label schematic stress-strain curves on the same graph [i.e., make separate plots for parts (a), (b), and (c)]. (a) Isotactic and linear polypropylene having a weight-average molecular weight of 120,000 g/mol; atactic and linear polypropylene having a weight-average molecular weight of 100,000 g/mol (b) Branched poly(vinyl chloride) having a degree of polymerization of 2000; heavily crosslinked poly(vinyl chloride) having a degree of polymerization of 2000 (c) Poly(styrene-butadiene) random copolymer having a number-average molecular weight of 100,000 g/mol and 10% of the available sites crosslinked and tested at 20 °C; poly(styrenebutadiene) random copolymer having a number-average molecular weight of 120,000 g/mol and 15% of the available sites crosslinked and tested at –85 °C. Hint: poly(styrene-butadiene) copolymers may exhibit elastomeric behavior. 15.33 For each of the following pairs of polymers, plot and label schematic specific volume-versustemperature curves of the same graph [i.e., make separate plots for parts (a), (b), and (c)]. of 25% crystallinity. random poly(styrene-butadiene) copolymer with 15% of available sites crosslinked (c) Polyethylene having a density 0.915 g/cm3 and a degree of polymerization of 2000 CES Problem Modern contact lenses must typically meet the following requirements: Optical quality in terms of optical transparency Low density Relatively good hardness and toughness Easy to mold (moldability rating of “5” minimum) In addition. spherulitic polystyrene.000 g/mol. We will evaluate the suitability of generic polymers (i.4 to 1. not specialized hydrogels or gas permeable polymers) for contact lenses.7). rigid or hard polymers that are gas permeable (lets oxygen gas pass through to the eye) or a hybrid of both types.985 g/cm3 and a degree of polymerization of 2500.2 – 2. Improvements have been made so that the newest contact lenses include soft hydrogels that are hydrophilic (water-loving). toughness and price range for each of the polymers in (1)? 3) What is the CO2 footprint for primary production of each of the polymers in (1)? As a comparison. currently contact lenses are made of polymers (“hard” or “soft”). of 25% crystallinity.e. Although silica glass was used in the first generation of contact lenses. contact lenses should have a refractive index suitable for bending light rays (typically between 1. and having a weight-average molecular weight of 75.4 kg/kg (mass of CO2 generated/mass of material) . the CO2 footprint for primary production of silica glass ~2. and having a weight-average molecular weight of 100. In the CES Edupack: Begin with Level 2 (EduLevel 2) Use the Tree stage to select only polymers and elastomers Use the Limit stage to input the necessary optical properties (see above) Use the Limit stage to input the necessary processability requirements (see above) Based on the requirements: 1) What polymers can be used for contact lenses? 2) What are the hardness. polyethylene having a density of 0.(a) Spherulitic polypropylene.000 g/mol (b) Graft poly(styrene-butadiene) copolymer with 10% of available sites crosslinked.