It's arbitrary really as the glass transition occurs over a temperature range. We normally quote peak tan delta but there are arguments to be made any number of other parameters. However, the onset of E' reduction would be more analogous to the brittle point.

There are three points you can mention: at the beginning (initial), peak (onset) and the end. Mostly, people report the onset or the peak (mid-one).

All the best.

Dear all, please check the following RG thread and the attached files. My Regards

https://www.researchgate.net/post/Whats-the-difference-between-measuring-Glass-Transition-Temperature-from-Storage-Modulus-Loss-Modulus-and-Tan-d-for-a-PMC-Which-is-more-reliable

Dear Asif Istiak . See the following useful link: https://www.tainstruments.com/pdf/literature/RH100.pdf

Kindly see also the following useful RG link: Article Comparison of mathematical models to predict glass transitio...

Also check please the following useful link: https://www.mdpi.com/1999-4923/2/2/78/pdf-vor

The following link is also very good: https://www.qualitymag.com/articles/92793-glass-transition-temperature-of-polymeric-materials

IT IS CORRECT TO REPORT ANY OF THREE OPTION, BUT I RECOMMEND TO REPORT THE TAN DELTA PEAK, DUE THIS SIGNAL IS THE RATIO BETWEEN LOSS MODULUS/STORAGE MODULUS,

The top peak of the tan Delta curve is taken as the Tg since it is very exact.

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Thank you all.

All of them are possible. But I have seen tan delta most of all

Please see my Doktor Vater, Prof. Christoph Schick and another Professor, Prof. Erst Donth's papers. The drop of G', peak of G" and peak of tandelta refers to relaxation with different length scales.

Asif, the Tg (when a polymer changes from the glassy state to rubbery state) occurs at the temperature where loss modulus begins to decrease. This temp difficult to measure accurately from thermogram so the sharp temp at Tan delta max is usually quoted as being Tg

Dr. Rui Zhang , thank you for your suggestion. May I have the DOI number or title of that article?

In most cases, the peak temperature in the loss modulus signal corresponds to the Tg determined by other thermal analysis techniques, such as DSC, TMA, and TR test (for elastomers).

It is my experience that the Tg of a polymer is usually quoted as being the temperature at which Tan delta max is recorded on a DMTA thermogram. It is a much sharper inflection peak transition than the

(i) temperature of inflection of the Storage Modulus on DMTA thermogram

(ii) temperature of inflection on a TMA expansion thermogram

(iii) on Temperature of inflection on a DSC thermogram.

Hope this helps.

DEAR ALL, ACCORDING WITH THEORY, THE VARIABLES CAN BE USE TO REPORT Tg VALUE, STORAGE MODULUS (E'), LOSS MODULUS (E") AND TAN DELTA, BUT DUE THE TAN DELTA IS DERIVED FROM E"/E' IT IS MORE REPRESENTATIVE FOR REPORT THIS IMPORTANT PROPERTY FOR POLYMERS, IN CASE YOU REPORT THE Tg USING DMA, IT IS IMPORTANT TO INDICATE WHICH OF 3 CURVES WAS USED FOR IT.