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.