I prepared co-polymer from propylene oxide and L-Lactide with Mn = 33.21Kg/mol and PDI = 1.44. When I recorded DSC (10o C/min) I am getting two Tg transitions (-17 oC and 8 oC). What could be the reason? Please suggest me.
Thank you in advance!
Hello dear possibly into the sample is present the copolymer and some homopolymer.
As suggested the two Tg-values indicate two seperate non mixed/seperated phases (like a blend or block like structure). In a homogeneous phase (copolymer) a single (often broader) Transition is expected. This should be the case for a random copolymer.
I would suggest to use e.g. DMA to get more Information about the process involved. Additionally a visualisation of the phase morphology would be useful.
Dear Dr. Matthias Jaunich
Many thanks for your help.
As Dr. Edwin A. Murillo and your expectations I have some homopolymer as side product. It seems I have to increase the reaction temperature from 80 to 100 oC.
Thank you all.
Try changing the stoichiometry to adjust to monomer reactivity ratio.
Dear Prof. Samui,
I have changed ratio of monomers. In few cases (for eg., 20:80 and 90:10) I have seen this Two Tg another cases single Tg was observed.
Thank you for your help.
Two Tg-values indicate two separate non mixed phases may be blend structure. In copolymer phase such kind of transition is expected.So may be check your stoichiometry.
Hello, everyone. In addition to the main question. Im looking for Tg for PVC plaque using DSC with (10 oC/min) velocity in argon atmosphere. The 10mg sample gave 71 o C onset Tg and after months when i take 10mg from same sample using DSC i get 63 o C onset Tg. What could be the problem?
You might also compare the Tg values to values you find in literature to get a hint About the incorporation of the monomers in your polymer chain. If you have some pure homopolymers the Tg should not Change a lot. However, if some monomers of one polymer (A) are incorporated randomly in a polymer of the other monomer (B), the Tg of B will be closer to A than of the pure homopolymer.
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