13C-NMR Analysis of Crosslinking Sites in Branched Polyesters
A detailed structural analysis of a four-component polyester based on adipic acid, isophthalic acid, neopentyl glycol (NPG) and trimethylol propane (TMP) is performed by l3C-NMR spectroscopy. The 13C resonances of the quaternary carbons of NPG and TMP are sensitive to all the possible different dicarboxylic acid combinations. All nine possible TMP polyester units are mimicked by synthesis of models with short well-defined adipic and/or isophthalic ester branches. The 13C resonance of the quaternary TMP carbon in each model corresponds exactly to one of the nine different resonances in the quaternary TMP polyester multiplet. This enables an unequivocal identification of three fundamental kinds of TMP structures in the four-component polyester: the four different crosslinking sites, the three linear segments and the two end groups. The four 13C resonances of the quaternary carbons of the crosslinking sites are evenly spaced by 0·4 ppm as a result of the stronger deshielding power of an isophthalate moiety when replacing the adipate analogue.
KeywordsAdipic Acid Quaternary Carbon Trimethylol Propane Crosslinking Site Isophthalic Acid
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