It is important to use high mass-resolution to analyze copolymers, which consist of two or more species of monomer. JMS-S3000 SpiralTOF™-plus 3.0 can separate many isobaric ion peaks (which have the same nominal mass but different accurate mass) on a mass spectrum. Since the mass spectra of copolymers are complicated, it is not practical to assign the peaks one by one. KMD analysis using msRepeatFinder makes it possible to visualize the distribution of polymer species. Below is the analysis example of an EO-PO block copolymer. The enlarged mass spectrum shows that peaks that are less than 0.03 u apart are clearly separated by a high mass-resolution. Visualizing the mass spectrum using a KMD plot (base unit: PO), a lattice is seen reflecting the PO distribution on the horizontal axis and the EO distribution in a diagonal direction. In addition, Fraction Base KMD plots provide a clearer visualization of the polymer series than conventional KMD plots.
Mass spectrum of EO-PO block copolymer
KMD plot (left) / Fraction base KMD plot (right)
From the pattern on the KMD plot, it is possible to know the ratio of the two monomers contained in the binary copolymer, or the difference in the synthetic process of the copolymers. Below are the mass spectra and KMD plots (base unit: PO) of two EO-PO copolymers with approximately equal average molecular weights. A small amount of PO homopolymer was detected on the mass spectrum and the KMD plot of the PO-EO-PO block copolymer. This is considered to be one of the proofs that this sample is a block copolymer, as the residual EO or PO homopolymers in the randomly polymerized EO-PO copolymers are unlikely given the process of synthesizing the copolymers.
On the other hand, for the EO-PO random copolymer, the KMD plot shows that the numeric distribution of EO monomers is wide. In addition, by specifying the end groups, the DP (degree of polymerization) plot can be generated, and the molar ratio and weight ratio of EO and PO can be calculated. The weight ratio of the PO-EO-PO block copolymers are in good agreement with the published values. It is possible to estimate the EO/PO composition ratios of the EO/PO random copolymer whose EO/PO ratio is not disclosed.
Mass Spectra of EO-PO random copolymer and PO-EO-PO block copolymer
Overlaid KMD plot of EO-PO random copolymer and PO-EO-PO block copolymer
DP plot of the EO-PO random copolymer
Molar ratio % |
Wight ratio % |
EO |
PO |
EO |
PO |
79.8 |
20.2 |
75.0 |
25.0 |
DP plot of the EO-PO block copolymer
Molar ratio % |
Wight ratio % |
EO |
PO |
EO |
PO |
46.8 |
53.2 |
40.1 |
59.9 |
Differential analysis of 2 polymer samples
The differential analysis of the end groups and molecular weight distributions of polymer samples is very important for checking the degradation of a sample, the difference between production lots, and the difference in the synthesis processes. msRepeatFinder (optional) can perform the differential analysis of two samples. Below is an application example used for the degradation analysis of polyethylene terephthalate. The bottom left shows the mass spectrum before and after degradation. Before degradation, cyclic oligomers, and after the degradation, the series having the COOH/COOH end groups were observed as major components respectively. In performing differential analysis, each sample was measured three times. The bottom right is the result of the differential analysis shown in the KMD plots. The red shows stronger peaks before degradation, while the green shows the stronger peaks after the degradation. In addition, a volcano plot can be created to confirm the components that differ with statistical significance between the 2 samples.
Mass spectra of PET samples before and after degradation
KMD plot of differential analysis result
Volcano plot of differential analysis result
msRepeatFinder (Option)
The Kendrick Mass Defect (KMD) plot and the Kendrick Mass Remainder (KMR) plot are used to estimate the polymer species and end groups contained in polymer materials from a complex mass spectrum and clarify their identity. In addition, the differential analysis function between two samples is effective in verifying sample degradation, lot-to-lot differences, and differences in the synthesis process.