..... because your PMMA is not a crystalline but amorphous polymer, which does not melt but undergoes the glass transition. You should consult polymer textbooks.

Best regards, J.V.

Dear all, 100Da is very low to consider it as a polymer. Contrary to crystalline zones, amorphous regions have different cohesion energies due to their irregularities, so their melting goes through a range (interval) of temperatures going from the least cohesiveness to the highest one. Molecular weight distribution also has its influence. My Regards

Gerard McNally

During DSC analysis it is the crystaline regions that melt and take in more energy to melt, hence the endotherm peak. PMMA is amorphous and so no distinct sharp peak is observed

We should qualify that PMMA produced free radically is amorphous. Synthesized anionically in polar solvents (ie THF) at low temperatures- syndiotactic PMMA can be made which can be crystalline. And synthesized with anionic catalysts- in solvents such as Toluene- at low temperatures- isotactic PMMA can be made which can also be crystalline but of a different structure and melting point than the syndiotactic PMMA.

As the answers are already there, I like to mention that PMMA is an amorphous polymer. If you expect to make crystalline, you have to synthesize via specific protocol. This has been mentioned by Steven.

You must be clear: if you want PMMA synthesized by free radical polymerization go ahead with amorphous polymer. Your DSC thermogram will show only Tg. However, your DSC is not correct. PMMA has glass transition temperature at 105 degree Celsius. Repeat the experiment.

PMMA is amorphous in nature. molecules are randomly arranged. melting point is nothing but the temperature at which phase transistion it means from solid phase(crystalls) to liquid state(dis orderd). takes place. amorphous polymers are already in disorder state there is no crystal to melt sharply instead they soften grdually as heat increases i.e (glass transition)