DSC Polymer Characterisation interpretation help

[Seeker3]

Hi respected peers,

Firstly, i must apologise in advance for any error i may make within this forum, I'm a new member here.
The question i wish to ask is with regards to observing a glass transition and crystallisation peak upon cooling, however without observing the obvious melt of a polymer being investigated. Is that possible?

I believe in theory you must have a melt peak before seeing crystallisation peak. However I am not an expert in this field to interpret such characteristics. The polymer investigated is a chemically synthesised dimercaptodithiin subsituted polyfuran. Powder XRD shown a small sharp peak at 10 A suggesting crystalline character.

In truth i am seeking an experts opinion to provide a little insight on how to correctly describe such a polymer. The glass transition and crystallisation peaks are prevalent in each consecutive heat-cool-heat cycles until degradation temperature has exceeded. Please find attached thermal history DSC graphs attached.

Any advice or further information would be highly appreciated.

Thank you kindly

 

[Kevin McHugh]

You don't have much going on there in terms of thermal events. It is very difficult to tell which is the first heat history and the last cycle. The only consistent thing I see is an exothermic event < 100^o C. Probably a T_g. But it does not appear your polymer has much crystallinity (if any). If you ran subsequent heat histories, with the first going up to 400^o C, the polymer has degraded, and any data after that us useless. I did see one endothermic peak. Integrate that peak to determine ΔH of fusion. Repeat several times to see if the the event is reproducible.

 

[Seeker3]

You don't have much going on there in terms of thermal events. It is very difficult to tell which is the first heat history and the last cycle. The only consistent thing I see is an exothermic event < 100^o C. Probably a T_g. But it does not appear your polymer has much crystallinity (if any). If you ran subsequent heat histories, with the first going up to 400^o C, the polymer has degraded, and any data after that us useless. I did see one endothermic peak. Integrate that peak to determine ΔH of fusion. Repeat several times to see if the the event is reproducible.

Good afternoon Kevin McHugh

Firstly, thank you kindly for taking your time out to check over my DSC graph traces and providing your valuable input. The thermal cycles provided were performed in four cycles with the methodology being;

First Run -50 to 150 degrees
Second Run-50 to ~180 degrees
Third run was from -50 to 300
Then last run from -50 to 400

I have attached a second run, in which i do the first cycle upto 125 degrees to remove any thermal histroy associated with the polymer. Then second cycle is ramped upto 275 degrees past polymer degradation.

I feared i had incorrectly assumed glass transition temp and upon cooling cycling a crystallisation peak. Therefore, for conclusion of these DSC graphs, I am unable to determine much thermal transitions of the polymer besides degradation temperature, possible Tg before 100 degrees and upon cooling the endothermic peak (which i assumed was polymer crystalline peak, but enthalpy of fusion?)


Thank you again
Seeker of Knowledge :)

 

[Kevin McHugh]

Definitely no crystallinity in that polymer. You should integrate the small peak to determine ΔH at that point, Still very small enthalpy.

 

[Seeker3]

Definitely no crystallinity in that polymer. You should integrate the small peak to determine ΔH at that point, Still very small enthalpy.

Good evening Kevin McHugh

Thank you for your further clarification. I shall definitely integrate the small enthalpy peak.

Kind regards

Seeker