Poly(Butylene Succinate) Molar Mass Calculation by GPC and 1H-NMR

The determination of the molar mass of a polymer is a fundamental characterization. One of the most common techniques used for this purpose is gel permeation chromatography (GPC). However, the most used columns are not appropriate for low molar mass polymers, presenting results that are different from reality. For these cases, it is possible to use the nuclear magnetic resonance (NMR) technique to obtain molar mass values (based on calculations associated with spectra signals and the quantity of the polymer used in the analysis). However, in some cases, the resultant signals of different chain portions can be presented in the same spectral region, hampering calculations. Thus, this paper proposes the use of an external standard. This way, it can correlate to the molar mass of four different samples of poly(butylene succinate) (PBS) with different molar mass values. The results based on NMR spectra were different from those found using GPC, but both increased in the same proportion (R-2 = 0.8828). Since NMR presents an absolute result, it seems to be the most accurate result. This analysis method also allows us to quantify the experimental percentage of unsaturation, which was lower than the theoretical one due to losses during the PBS synthesis.

Automated summary

The paper discusses the determination of molar mass of polymers, highlighting limitations of current techniques and proposing the use of NMR with an external standard to improve accuracy of results.