I made three polyester polyols.
1) phthalic anhydride+ diethylene glycol(DEG)
2) terephthalic acid+ DEG
3) isophthalic acid+DEG
Viscosity is 1
Dear Dohyeong Kim, this is due to the differences in reactivity of the different carboxylic acids in each compound. This leads to high chain lengths (high MW and high viscosity) for the most reactive and low chain lengths for the least reactive one. Please check the attached file. My Regards
Dear Dohyeong Kim, this is due to the differences in reactivity of the different carboxylic acids in each compound. This leads to high chain lengths (high MW and high viscosity) for the most reactive and low chain lengths for the least reactive one. Please check the attached file. My Regards
I would also ascribe differences of viscosity to MW than to the architecture of the polymer or presence of impurities. Therefore, good solution of the problem is acid/hydroxyl number determination.
BTW: Kirk-Othmer is not up-to-date here (chemical tech is now in very different point), however, properties of acids were correctly described.
Michal J Kalita
thank you for your answer.
if the hydroxyl numbers of these polyols are same, then do you think that mw of isophthalic acid polyols is the biggest?
hydorxyl numer is about 280.
When Isophthalic acid and Phthalic anhydride are mixed to synthesize polyol, the viscosity is lowered. This is seen as a structural difference, what do you think? What do you think lowers the viscosity of the Phthalic anhydride structure and what lowers the viscosity of the terephthlaic acid?
One of the possibilities is formation of macrocycle (diester of DEG and Phthalic Acid). See e.g. patent US3431279A. In general, topic need quite deep research in order to define architecture of the resulting product(s). No idea why Terephthalic acid-based systems can be lower than that of Isophthalic Acid with similar MW.
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