NMR spectroscopy allows to observe the percentage of each acylglycerides in the polyester structure. Chemical shifts of these structures could be found in our previous work. Moreover, the changes during the reaction could be observed due to samples probing in a time interval (Figure ). The reaction at 120°C is the best to observe it because it is the slowest experiment performed in this study. It could be clearly seen that glycerine is fully conversed after about 2 hours of reaction. At that time, the conversion of the carboxylic group is about 58%. The first reaction step is the production of monoacylglycerides. Due to the higher reactivity of primary hydroxyl groups T1 acylglycerides are mainly produced, but it could be seen that T2 acylglycerides immediately react to obtain L1,2 diacylglycerides. The concentration of L1,2 diacylglycerides increases slowly and, after about 200 min stays at a level of ca. 18%. A much faster increase in the percentage of L1,3 diacylglycerides could be observed. However, when glycerine is fully conversed, it decreases by increasing the concentration of D triacylglycerides. It is surprising because L1,2 diacylglycerides have a free primary hydroxyl group, which should be more reactive than the secondary hydroxyl group in L1,3 diacylglyceride. Meanwhile, the concentration of L1,2 diacylglycerides is pretty stable at this reaction moment. These correlations are also observed at higher temperatures. The temperature did not affect the reaction mechanism in this study.