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Homework Help: Polymer Physics: molar mass, polymerization

  1. Sep 12, 2017 #1
    1. The problem statement, all variables and given/known data
    Consider a “true macromolecule” - a chunk of polybutadiene network
    of mass 100g. How many monomers all covalently bonded together
    does it contain if the molar mass of the monomer is
    Mmon= 54g/mol?
    What is the molar mass of this macromolecule?

    2. Relevant equations

    Molar mass of polymer = polymerization * Molar mass of monomer

    3. The attempt at a solution

    It seems I have two unknowns in my equation of three variables. The biggest issue is that I'm unsure what the relevance of the 100g sample is. None of the textbook examples or online examples that I've found are structured this way. They always give a molar mass/molecular weight of the polymer.

    100g / 54g/mol says that 1.96 moles of the monomer can "fit" into the 100g sample of the polymer. Though I'm not sure how relevant that is. Based on the order of the two questions, it seems I need to find the degree of polymerization first.
  2. jcsd
  3. Sep 13, 2017 #2


    User Avatar

    Staff: Mentor

    My reading of this is that the 100g chunk is a single molecule (all the monomers are bonded to each other).
  4. Sep 13, 2017 #3


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    Science Advisor

    "Network" would imply that it is cross-linked, though I'm not sure if that's what they really mean or they're just being sloppy. Certainly a linear polymer with a degree of polymerisation of 1024 would be very unusual.
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