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32.6: Summary

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    You should now be familiar with the following concepts:

    • Above Tg polymers are rubbery, whereas below Tg they are glassy
    • Rubbery behaviour arises from the polymer's ability to change its conformation at high temperatures
    • Glassy behaviour arises from the polymer's lack of ability to change its conformation at low temperatures
    • Many factors affect the Tg of a polymer. Some factors are to do with the chemistry of the polymer:
      • chain length
      • chain flexibility
      • side groups
      • branching
      • cross-linking
      • the presence of plasticisers

      Other factors are to do with the method of measuring Tg:

      • strain rate
      • cooling or heating rate
    • You should also understand the theory of kinetics, which explains how glasses form and noted that there are many different experimental methods for measuring the glass transition temperature in polymers.
    • Finally you should have observed how the behaviour of a rubber ball varies when it is bounced above, below and near its Tg and seen how the behaviour of silly putty varies at different strain rates.

    Going further


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