Ajay... The study of organic compounds by TG and DSC techniques is very interesting. The compound must purified to dismiss any signal that may come from impurities. The presence of impurities will highly alter the melting points of the compounds. Between 1982 and 1990 I published a series of articles on the thermal analysis of variety of compounds. Some of them are given here for your interest.

Thermochimica Acta, 177 (1991) 329.

Thermochim. Acta, 138 (1989) 13-20.

Thermochim. Acta, 79 (1984) 139.

You have melting, thermal decomposition. The signals are highly affected by the substituents and the the presence of good leaving groups.

If you give me some details about the compositions and send me the electronic signals, I may be of some help... Regards

The effect causing the peak at 174°C is definetely not a glass transition. I think it is evaporation of some components which would fit to the mass loss observed in TGA.

In general a Tg should show a step like characteristic in the heat flow curve in the direction of endothermal events (due to the increase in cp).

Am i correct when i assume that the other lines in the figures are cooling and second heating? Why do they not show any events?

Dear, Prof. Mahmood M. Barbooti and Dr. Matthias Jaunich.

Thanks a lot for the valuable suggestion. The NMR of the compound 2 shows some DCM molecules. Since I used the crystals for the measurement, its contains DCM molecule in the crystal. Would removable of DCM shows peak at 174 °C in DSC?

As Dr. Matthias point out that second cycle of DSC curve does not show any peak, might be because of the decomposition at the end of first cycle.

I wounder if I fixed the range of DSC measurement to 300 °C, it would exhibits similar peak pattern during second cycle? It might give a insight for the appearance of peak at 174 °C.

Here, I attached the representative structure of compounds. I would be very grateful if you could explain the appearance of peak at 258 °C.

Thank you.

Dear Ajay, normally we perform DSC analysis below the decomposition temperature to effectively monitor the reversible transitions. As Prof Matthias mentioned, there is a weight loss in the TGA profile below 200 possibly due to the loss of some residues. This may have some role in giving extra peaks in DSC. We used to take second heating curves from DSC for eliminating the effect of possible moisture or other volatile impurities.

with best regards

Renjith

Dear Dr. Renjith,

Thanks for the valuable suggestion.

Recently, I have checked the melting point of the compound 2, it melted at 174°C.

And also, TGA curve shows that the compound is stable at 300°C. So I fixed the range of DSC measurement to 300 °C, but I got the similar curve.

I would greatly appreciate any further suggestions.

Dear Mr. Ajay Kumar

DSC analysis is a very common technique to investigate the phase behavior of the materials. There are several factors that strongly influence the DSC trace. First, you need to make sure that your compounds are completely purified and dried. Second, the DSC machine should be well maintained. For example, as seen from TGA curve, there is a weight loss near 200oC which may come from the impurities or residual solvents.

After these, if the DSC traces are still the same, why dont you consider to analyze your compounds by other techniques such as XRD. XRD may give you an insight of your molecular assembly which may answer your question. Because only small variation of molecular design can sometimes lead to a remarkable difference in molecular assembly which directly affects DSC traces

Dear Mr. Linh Nguyen Manh,

Thanks for the valuable suggestion. I am going to obtain the XRD, which might give some insight. Thanks