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
- 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.
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