Tg and TM can be measured experientally by plotting (AV/ AD, a characterization

Question

Tg and TM can be measured experientally by plotting (AV/ AD, a characterization 2. technique known transitions is by thermal analysis - observing endotherms or exotherms - through differential thermal analysis (DTA) or diff. scanning calorimetry (DSC). Re-read Allcock's discussion of DSC/DTA Chapter 17 pp. 540 546 approx. (depends on which edition you have). [30 pts] (a) During the transition from the glassy as dilatometry. A more convenient method of determining these state to the rubbery state, a polymer will absorb energy as the temperature passes through Tg. Are bonds of any type being broken during this transition? (b) Which has the higher specific (intrinsic) heat capacity (amount of heat necessary to raise sample's temperature by one degree) - a polymer sample below its Tg or above its Tg? (c) Many polymer samples will experience an exotherm (as determined by differential scanning calorimetry) between points Tg and TM if heated slowly enough. What is occurring?

Explanation / Answer

Polymers

Polumers when heated passes through Tg and Tm

(a) During the transition from the glassy state to the rubbery state, secondary intermolecular bonds between the chains of the polymers are broken during this glassy to rubbery state transition.

(b) The specific heat is the amount of heat needed to raise the temperature by one degree celsius. The heat needed or the specific heat for the polymer sample above its Tg would be higher than the one below its Tg.

(c) Many polymers experience an exotherm when slowly heated between its Tg and Tm. The less-ordered amorphous state at the Tg passes to a more-ordered crystalline state as it goes to its Tm. This thus gives the typical exotherm in some polymers.

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