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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 modulus than the other; (2) if this is possible, note which has the higher tensile modulus and cite the reason(s) for your choice; and (3) if it is not possible to decide, state why. (a) Branched and atactic poly(vinyl chloride) with a weight-average molecular weight of 100,000 g/mol; linear and isotactic poly(vinyl chloride) having a weight-average molecular weight of 75,000 g/mol (b) Random styrene-butadiene copolymer with 5% of possible sites crosslinked; block styrene–butadiene copolymer with 10% of possible sites crosslinked (c) Branched polyethylene with a number-average molecular weight of 100,000 g/mol; atactic polypropylene with a number-average molecular weight of 150,000 g/mol

For the following pair of polymers, do the following: (1) state whether it is possible to decide if 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, state why not. $\bullet$ Syndiotactic polystyrene having a number-average molecular weight of 600,000 g/mol $\bullet$ Isotactic polystyrene having a number-average molecular weight of 500,000 g/mol

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 cite the reason(s) for your choice; and (3) if it is not possible to decide, state why. (a) Linear and isotactic poly(vinyl chloride) with a weight-average molecular weight of 100,000 g/mol; branched and atactic poly(vinyl chloride) having a weight-average molecular weight of 75,000 g/mol (b) Graft acrylonitrile–butadiene copolymer with 10% of possible sites crosslinked; alternating acrylonitrile–butadiene copolymer with 5% of possible sites crosslinked (c) Network polyester; lightly branched polytetrafluoroethylene

Question

For the following pair of polymers, do the following: (1) state whether it is possible to decide if one polymer has a higher tensile modulus than the other; (2) if this is possible, note which has the higher tensile modulus and then cite the reason(s) for your choice; and (3) if it is not possible to decide, state why not. $\bullet$ Syndiotactic polystyrene having a number-average molecular weight of 400,000 g/mol $\bullet$ Isotactic polystyrene having a number-average molecular weight of 650,000 g/mol

Solution

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Tensile modulus is independent of molecular weight. Additionally, both forms of polystyrene will crystallize. Therefore it is $\boxed{\text{Not possible}}$ to determine which has the higher tensile modulus.