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a) A student is asked to find the glass transition temperature of a sample of high molecular weight atactic polystyrene.
1. 1. a) A student is asked to find the glass transition temperature of a sample of high molecular weight atactic polystyrene. He does not have a differential scanning calorimeter (DSC), so he decides to send samples of the same polymer to two different companies to analyze by DSC. One company reports a Tg of 100°C while the second company reports at Tg of 107°C. Both companies used 5.0 mg of sample from the same batch of pure polymer and determined the glass transition temperature from the second scan. What piece of information on the testing conditions is missing?
b) Why is the glass transition temperature of glassy polymers normally determined after the second heating in a DSC?
c) A scientist purchases two samples of pure polystyrene. One is opaque and the other is not. The chemical structure of both is the same. What is the difference between the two samples?
d) A scientist purchases a sample of high density polyethylene and a sample of low density polyethylene. DSC reveals a glass transition in one sample but not the other one. Which sample is more likely to exhibit a Tg and why?What structural features are responsible for the difference in thermal properties? The polymers contain no additives.
e) Is the glass transition temperature more representative of a first order transition or a second order transition and why?
