A protocol for quantitative sequential 13C NMR analysis is developed for polyesters composed of trimethylol propane (TMP), neopentyl glycol (NPG), and adipic and isophthalic acids. TMP centred, structural models with methyl adipate and isophthalate branches in all possible combinations are synthesized and purified. A detailed 13C NMR investigation of the models unequivocally allows the identification of the TMP polyester structural sequences through the quaternary TMP carbon multiplicity. Spin-lattice relaxation times, T1, of model quaternary TMP carbons are in the 2.3–5.2 s range, depending on the size of the specific model. This relaxation behaviour defines the experimental conditions for obtaining the quantitative assessment of all polyester polyol structural sequences based on quaternary TMP and NPG carbons. The special case dealt with here additionally centers all acid moieties between poyols in triads and thus makes quantitative determinations of all polyester constituents possible.