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Article

MALDI-TOF Mass Spectrometry as the Tool for the Identification of Features of Polymers Obtained by Inverse Vulcanization

by
Natalia Tarasova
1,
Efrem Krivoborodov
1,*,
Diana Kirakosian
1,
Alexey Zanin
1,
Ilya Toropygin
2 and
Yaroslav Mezhuev
1,3
1
Institute of Chemistry and Problems of Sustainable Development, D. Mendeleev University of Chemical Technology of Russia, 125047 Moscow, Russia
2
V. N. Orekhovich Research Institute of Biomedical Chemistry, Russian Academy of Sciences, 119121 Moscow, Russia
3
Nesmeyanov Institute of Organoelement Compounds, Russian Academy of Sciences, 119334 Moscow, Russia
*
Author to whom correspondence should be addressed.
Macromol 2024, 4(4), 856-870; https://doi.org/10.3390/macromol4040050
Submission received: 30 October 2024 / Revised: 1 December 2024 / Accepted: 6 December 2024 / Published: 8 December 2024
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Abstract

:
The MALDI-TOF mass-spectrometry was employed to analyze the structure of the reaction products of limonene, a natural terpene, and elemental sulfur, with the objective of identifying the occurrence of side processes, such as oxidative dehydrogenation, aromatization, and the Diels–Alder reaction cascade. The MALDI-TOF mass-spectrometry was demonstrated to be effective for the analysis of high-sulfur polymers obtained by the inverse vulcanization reaction, allowing for the unambiguous separation of sulfur-containing and hydrocarbon molecular fragments and the detailed characterization of macromolecular structures. By varying the ratio of sulfur (S8) and limonene in the initial reaction system, we were able to ascertain the limiting amount of sulfur that can be covalently bonded by terpene, as well as determine the average length of polysulfide chains under the assumption of equal reactivity and complete depletion of all double bonds. The side reaction of limonene aromatization, as indicated by the MALDI-TOF spectrum of the product resulting from its interaction with elemental sulfur, was corroborated by 1H and 13C NMR spectroscopy. Consequently, the registration and interpretation of MALDI-TOF spectra of inverse vulcanization products, either independently or in conjunction with the application of 1H and 13C NMR spectroscopy methods, as well as the determination of the limiting number of sulfur atoms that can be bound to one molecule of an unsaturated compound, paves the way for new avenues of investigation into the structure and side reactions involved in the synthesis of high-sulfur polymers.

Graphical Abstract

1. Introduction

Despite the fact that elemental sulfur is a readily available raw material derived from natural sources, its production consistently exceeds consumption [1,2]. In this regard, the processes of obtaining high-sulfur macromolecules through the interaction of unsaturated compounds, such as divinylbenzene [3,4,5,6], diisopropenylbenzene [7,8,9,10,11,12], styrene [13,14,15,16], limonene [17,18,19,20], squalene [21,22,23,24], myrcene [25,26,27], and unsaturated fatty acids [28,29,30,31,32,33] with S8 are of considerable interest. The polymers obtained by this reaction can have a different molar mass (102–105 g/mol) and possess an acceptable complex of physical and mechanical properties [9,16], as well as significant heat resistance [5,6,16]. The products of the reaction of sulfur with unsaturated compounds show promise as materials for the fabrication of cathodes for lithium-sulfur batteries [34,35,36,37,38,39,40,41,42], infrared optics [43,44,45,46,47,48], and sorbents for water treatment and the extraction of heavy metal cations [49,50,51,52,53,54,55,56]. Despite the extensive research conducted on the inverse vulcanization reaction, the majority of studies in this field have concentrated on the regulation of properties and the design of polymers with specific functions [34,35,36,37,38,39,40,41,42,43,44,45,46,47,48,49,50,51,52,53,54,55,56]. However, there is still a lack of clarity regarding the underlying mechanism and the occurrence of numerous side reactions. The latter is attributable, at least in part, to the established methodology for the study of inverse vulcanizations products, which includes gel permeation chromatography [57,58,59,60,61], Raman spectroscopy [38,62,63,64,65,66], IR spectroscopy [63,64,65,66,67], UV-vis spectroscopy [15,64,68,69,70], and 1H, 13C NMR spectroscopy [7,14,71,72,73,74] and various elemental analysis approaches, including XPS [3,6,42,75,76], EDX [33,64,65,77,78,79,80], and ICP-OES [6]. The aforementioned methods permit the acquisition of valuable data regarding the composition and structure of high-sulfur polymers. However, in certain instances, they may prove inadequate for the detection of side reactions occurring under inverse vulcanization conditions. The utilization of a series of mass spectrometry techniques to examine the products of the interaction between unsaturated compounds and elemental sulfur is confined to a limited number of documented instances. These include the methodologies employed for the recording of spectra generated by CIS-MS [17], ToF-SIMS [73,75], and APCI-MS [21]. Concurrently, the MALDI-TOF mass-spectrometry, which has been extensively employed for structural investigations and the semi-quantitative estimation of the molecular-weight distribution of polymers [81,82,83,84,85], is seemingly underestimated for the analysis of inverse vulcanization products. As will be demonstrated subsequently, high-sulfur polymers desorb with decomposition into charged fragments under MALDI-TOF recording conditions. However, the identification of their structure can provide valuable insight into the nature of side reactions in inverse vulcanization processes. A further crucial aspect of inverse vulcanization processes is the existence of a limiting length of polysulfide fragments, at which they lose thermodynamic stability. This implies that there is a limiting capacity for elemental sulfur, which can be bound covalently, in unsaturated compounds. It is established that high-molecular-weight plastic sulfur loses its thermodynamic stability at temperatures below the lower critical temperature of polymerization [86]. This phenomenon indicates the potential for depolymerization of polysulfide bridging groups with lengths, exceeding a certain threshold, at room temperature.
The present article is devoted to the application of the MALDI-TOF mass-spectrometry for the establishment of side reactions in the inverse vulcanization process and the development of a technique for determining the ultimate capacity of unsaturated compounds by the elemental sulfur assimilated by them. The example of the interaction between the model terpene (limonene) and S8 is used to illustrate these points.

2. Materials and Methods

2.1. Materials

Elemental sulfur with a purity of more than 99% produced by “Reachim” (Moscow, Russia) and D-limonene purchased from “Merck” (Darmstadt, Germany) ( with the content of the basic substance of 98.5% were used for the inverse vulcanization reaction. Chloroform from “Merck” (Darmstadt, Germany) was used to dissolve the obtained polymer in order to determine the mass of unreacted sulfur residue.

2.2. Interaction of D-Limonene and Cyclooctasulfur (Synthesis of High-Sulfur Polymer by Inverse Vulcanization Reaction)

The elemental sulfur powder was subjected to a heating process at a temperature of 125 °C, with the use of a thermostat. D-limonene was subsequently added to the molten sulfur in order to achieve the following mass ratios of reactants: the ratios of the reactants were 1:4, 1:6, 1:8, 1:10, 1:12, 1:14, and 1:16. Subsequently, the temperature was increased to 165 °C and the resulting reaction system was incubated for 20 min. The resulting product was then cooled to room temperature at a slow rate and transferred to a vial by the addition of chloroform. It was then incubated for one hour to allow the polymer to dissolve. Subsequently, the precipitate was separated and washed once more with chloroform. Once the polymer had been fully removed, the elemental sulfur precipitate was dried and weighed. The amount of sulfur included in the polymer was determined by the difference between the weight of the initial sulfur and the weight of the sulfur remaining after the inverse vulcanization and dissolution of the synthesized polymer.

2.3. Methods for the Study of a Polymer Obtained by the Interaction of D-Limonene and Elemental Sulfur

The structure of the synthesized polymer (initial mass ratio S8/D-limonene = 4) was determined by MALDI-TOF mass spectrometry, 1H and 13C NMR spectroscopy. MALDI-TOF spectra were recorded on an Ultraflex II mass spectrometer (Bruker, Bremen, Germany) with the detection of anions and cations in reflector mode with an accelerating voltage of 25 kV. Desorption was carried out by Nd:YAG laser with a wavelength of 355 nm (3.5 eV), without the use of a matrix. In total, 0.5 μL of the polymer solution in CHCl3 with a concentration of 0.01 g/mL was applied to a ground steel MALDI target plate (MTP) from “Bruker Daltonics”. After the evaporation of the chloroform for 5 min, the MALDI-TOF mass spectrum was recorded. Although no matrix was used in the recording of mass spectra in this paper and the spectra obtained are LDI, the abbreviation MALDI-TOF will be used in further discussion of the results, as it is more frequently used in the literature even when the spectra were recorded without a matrix. Taking into account the possibility of laser desorption from MTP of non-polar and devoid of pronounced acid-base properties products of inverse vulcanization of limonene, as well as complications in interpreting spectra of signals caused by the presence of a matrix, in this work the laser desorption of macromolecules was carried out in the absence of a matrix.
The 1H and 13C NMR spectra were recorded in a CDCl3 medium (polymer concentration 0.1 g/mL) on a Bruker Avance 400 DPX spectrometer (Bruker, Germany) at 20 °C.

3. Results and Discussion

Since natural, elemental sulfur has four stable isotopes 32S, 33S, 34S, and 36S, the content of which is 95.02%, 0.75%, 4.21%, and 0.02%, respectively [87], it is possible to identify signals of fragments containing and not containing sulfur atoms in MALDI-TOF mass spectra of inverse vulcanization products. In particular, when interpreting the MALDI-TOF mass spectrum of the product of the interaction of elemental sulfur with the model terpene limonene (Figure 1A), the presence of a group of fragment signals with m/z equal to 133, 135, 137, 287.3, 315.3, and 371.4, which do not contain sulfur atoms, and fragment signals with m/z 165, 167, 169, 197, 199, and 201, which contain sulfur atoms and give accompanying isotope signals with an isotopic distribution pattern close to the theoretical one, was noted.
The presence of signals with m/z 133 and 135 (Figure 1B) is consistent with the assumption of partial oxidative dehydrogenation of limonene with subsequent aromatization, accompanied by the formation of 4-methylisopropenylbenzene (III). The signal with m/z 137 (Figure 1B) can be attributed to the protonation products of the initial limonene. The detection of cations corresponding to protonated molecules (I), (II), and (III) indicates the formation of compounds with pronounced acidic properties in the system, which are presumably hydrogen polysulfides (Figure 2).
The activity of limonene (I) and the products of its oxidative dehydrogenation (II) (III) in the reaction with cyclooctasulfur has been confirmed by the presence of groups of signals with m/z 169, 167, and 165, which correspond to [C10H17S]+, and [C10H15S]+. Furthermore, the presence of the ions [C10H13S]+ and those with m/z 201, 199, and 197, corresponding to the cations [C10H17S2]+, [C10H15S2]+, and [C10H13S2]+ (Figure 2) was also confirmed. A comparison of the experimental isotopic distribution for the fragments [C10H17S]+ and [C10H17S2]+ with the theoretical one calculated using the program “Iso Pro 3.1” indicates a high degree of correspondence between the two (Figure 3).
Given that the molecular mass of the limonene corresponds to m/z 136.24, the presence of signals with m/z equal to 287.3, 315.4, and 371.4 in the MALDI-TOF mass spectrum (Figure 4) belonging to fragments devoid of sulfur atoms, indicates secondary transformations of this terpene, which occur in the presence of cyclooctasulfur, which acts as the oxidizing agent.
It seems reasonable to posit that following the formation of compound (II) as the result of the oxidative dehydrogenation of limonene (Figure 2), a cascade of Diels–Alder reactions ensues, culminating in the generation of limonene trimers with a structural resemblance to compound (VI) (Figure 5). As can be observed, compound (VI) lacks diene fragments and all its double bonds are sterically hindered, preventing further participation in the Diels–Alder reaction. This may explain the absence of signals for hydrocarbon fragments containing no sulfur atoms with m/z exceeding 371.4. Figure 5 illustrates the potential structures of fragmentation products (VI) (or their isomers) with m/z 287.3, 315.3, and 371.4, which were identified during MALDI-TOF mass spectral registration. The primary pathways of fragmentation for compound (VI) are likely to be the Diels–Alder retro-reaction, dehydrogenation, and methane loss. In addition, the MALDI-TOF mass spectrum contains extended sequences of signals with an m/z difference of one unit with peaks dominating in intensity with m/z equal to 290.9, 319.8, 351.8, and 385.4, corresponding to cations formed from sulfur-containing fragments (VII)–(X) included in the macromolecules (Figure 5).
The putative compounds (II)–(VI) (Figure 5), as well as the initial limonene, contain double carbon–carbon bonds and are thus capable of reacting with S8. It would appear that the CH2=CR2 double bonds of the acyclic fragments are the most active in the interaction with cyclooctasulfur, as evidenced by the lack of signals with chemical shifts around 110 ppm and 150 ppm in the 13C NMR spectrum (Figure 6A), which are characteristic of this fragment. Concurrently, multiple bonds within the cyclic fragments are partially preserved, as evidenced by the presence of signals with chemical shifts of 120–130 ppm in the 13C NMR spectrum of inverse vulcanization products (Figure 6A). The 1H NMR spectrum (Figure 6B) displays proton signals with chemical shifts of 7.0–7.6 ppm, which corroborates the oxidative aromatization of limonene under the conditions of its reaction with S8. This phenomenon has previously been documented in the literature [19,88,89]. It can thus be surmised that the presence of signals with a chemical shift of 120–130 ppm in the 13C NMR spectrum (Figure 6A) may be attributed to aromatization, given that the double bonds of the benzoic ring are inactive in inverse vulcanization. The 13C NMR and 1H NMR spectroscopy data indicate the formation of a complex mixture of hydrocarbons and the corresponding polysulfides, which is consistent with the MALDI-TOF mass spectrometry data on positively charged ions discussed above. Although the identification of the structure of individual links of the polymer chain using NMR spectroscopy data is difficult due to the formation of their complex mixture, the presented results allow us to conclude that the dehydrogenation of limonene is not a consequence of destructive processes under conditions of laser ionization/desorption of macromolecules, since the formation of the corresponding fragments is independently shown by 13C NMR and 1H NMR spectroscopy methods using low-energy radio wave radiation.
The MALDI-TOF spectrum reveals the presence of anion signals from S 2 − to S 7 − in the low molar mass region, concomitant with the observation of signals of [C10H17Sn]− fragments in the high molar mass region (Figure 7).
The series of signals from S 2 − to S 7 − are caused by the destruction of polysulfide bridges between hydrocarbon residues in the macromolecular chain. The signals [C10H17Sn]− observed during the detection of anions are related in origin to the signals [C10H17Sn]+ found in the cation detection mode (Figure 3) and are a consequence of the formation of fragment ions containing limonene residues and sulfur atoms (Figure 8). The driving force for the formation of fragment ions is the relative lability of S–S bonds in long polysulfide sequences [90].
The study of the reaction products of cyclooctasulfur with unsaturated compounds by MALDI-TOF spectrometry offers a promising avenue for elucidating the structural details of synthesized macromolecules. This is achieved by considering the potential mechanisms of their destruction at laser ionization (Figure 8). Additionally, this approach serves as a robust method for identifying side reactions in inverse vulcanization processes. On the other hand, the possibility of using MALDI-TOF mass spectrometry to determine the structural details of the products of inverse vulcanization of the natural terpene limonene is an expansion of the scope of this method, which has proven itself to be a reliable tool for the analysis of many biopolymers [91,92], their derivatives and polymers for pharmaceutical purposes [93].
A further crucial element of the synthesis of sulfur-containing polymers via the interaction of unsaturated compounds and S8 is the inability to achieve covalent bonding of more than a specific number of sulfur atoms. This is due to the fact that polysulfide sequences become thermodynamically unstable as their length increases [94]. It is established that polymeric sulfur is unstable at temperatures below the lower critical temperature of polymerization, resulting in depolymerization and the formation of the initial cyclooctasulfur [95]. It is therefore essential to establish the ultimate sulfur capacity of unsaturated compounds, that is to say, the maximum amount of sulfur that can be covalently assimilated. The inverse vulcanization process was conducted at varying initial ratios of sulfur/limonene, followed by the dissolution of the resulting polymer in chloroform and the determination of the residual amount of unreacted sulfur. This approach enabled the establishment of two key observations: firstly, that the mass of unreacted sulfur increased in proportion to the amount present in the reaction system, and secondly, that the amount of sulfur incorporated into the polymer remained constant at a significant excess of S8 (Table 1).
The mass of unreacted elemental sulfur present in the final mixture is found to be dependent upon the molar ratio of sulfur and limonene present in the initial mixture. This dependence is linear (Table 1, Figure 9) and can be described by the following Equation (1):
n e x S = 3.7 × 10 − 3 n ( S ) n ( L i m o n e n e )
where n e x S —number of moles of unreacted sulfur, n S , and n ( L i m o n e n e ) —number of moles of sulfur and limonene in the initial mixture.
It can be demonstrated that the limiting amount of sulfur that can be covalently bonded by one mole of limonene is equal to the value of the amount of unreacted sulfur, n e x S = 0. This implies that, on average, approximately 17 sulfur atoms can be bonded by one limonene molecule. This figure corresponds to the inclusion of an average of 4.25 sulfur atoms per carbon atom of the double bonds of the original limonene (seventeen sulfur atoms per four carbon atoms of the two double bonds of limonene). The mean length of polysulfide bridges is 8.5 sulfur atoms when the conditions of equal reactivity and complete conversion of all double bonds of limonene are met. As evidenced by NMR spectroscopy data (Figure 6), a portion of the double bonds present within the cyclohexene fragments of limonene are retained in the products of inverse vulcanization, suggesting the presence of polysulfide bridges with an average length exceeding 8.5 sulfur atoms.

4. Conclusions

The application of the MALDI-TOF mass-spectrometry to analyze the structure of limonene inverse vulcanization products has been demonstrated to facilitate the registration of an informative spectrum of high-sulfur polymer degradation. The advantage of MALDI-TOF mass spectrometry is that it allows for the separation of signals from molecular fragments containing and not containing sulfur atoms based on the character of the isotopic distribution. Additionally, it enables the identification of side transformations of unsaturated compounds under conditions of interaction with cyclooctasulfur. In the inverse vulcanization of limonene, additional processes were observed, including oxidative dehydrogenation and aromatization of the initial terpene, as well as the activity of the monodehydrogenation product of limonene in successive Diels–Alder reactions, which led to the formation of polycyclic molecules. By varying the ratio of elemental sulfur and limonene in the initial reaction mixture, it was determined that limonene is capable of binding no more than seventeen sulfur atoms, with the average length of polysulfide bridges slightly exceeding 8.5 sulfur atoms. Therefore, the utilization of a combination of MALDI-TOF mass spectrometry techniques and the determination of the maximum capacity of unsaturated compounds for sulfur atoms enables the characterization of the details of the structure of inverse vulcanization products, the identification of which by other methods is challenging. Furthermore, this approach facilitates the detection of side reactions in the synthesis of high-sulfur polymers. Thus, the presented results not only provide new opportunities for analyzing the structure and mechanism of the formation of reverse vulcanization products of natural and synthetic unsaturated compounds, but also expands the scope of the application of the MALDI-TOF method, traditionally used to study biopolymers.

Author Contributions

Conceptualization, N.T., E.K. and Y.M.; methodology, E.K. and I.T.; software, A.Z. and E.K.; validation, N.T. and Y.M.; formal analysis, I.T., E.K., N.T., E.K. and Y.M.; investigation, E.K., A.Z., I.T. and D.K.; resources, N.T.; data curation, N.T. and E.K.; writing—original draft preparation, E.K., D.K. and Y.M.; writing—review and editing, N.T. and Y.M.; visualization, D.K. and A.Z.; supervision, N.T. and E.K.; project administration, N.T.; funding acquisition, N.T. All authors have read and agreed to the published version of the manuscript.

Funding

The work was supported by the Russian Science Foundation, project no. 23-23-00543.

Data Availability Statement

The original contributions presented in this study are included in the article. Further inquiries can be directed to the corresponding author(s).

Acknowledgments

The authors express their gratitude for the assistance in the preparation of the manuscript to the Network center for advanced research “Green Chemistry for Sustainable Development: from fundamental principles to new materials” and the D.I. Mendeleev Center for Collective Use.

Conflicts of Interest

The authors declare no conflicts of interest.

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Figure 1. MALDI-TOF mass spectrum of the reaction product of elemental sulfur with limonene in the m/z 100–1000 (A) region, as well as at m/z < 205 (B), recorded in reflector mode with cation detection.
Figure 1. MALDI-TOF mass spectrum of the reaction product of elemental sulfur with limonene in the m/z 100–1000 (A) region, as well as at m/z < 205 (B), recorded in reflector mode with cation detection.
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Figure 2. Oxidative dehydrogenation of limonene with elemental sulfur and putative structures of cations detected in the MALDI-TOF mass spectrum.
Figure 2. Oxidative dehydrogenation of limonene with elemental sulfur and putative structures of cations detected in the MALDI-TOF mass spectrum.
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Figure 3. The experimental and theoretical (constructed using the program “Iso Pro 3.1”) isotopic distributions of signals for cations: (a)—[C10H17S]+ and (b)—[C10H17S2]+ detected in the MALDI-TOF mass spectrum of the product of the interaction of limonene with elemental sulfur.
Figure 3. The experimental and theoretical (constructed using the program “Iso Pro 3.1”) isotopic distributions of signals for cations: (a)—[C10H17S]+ and (b)—[C10H17S2]+ detected in the MALDI-TOF mass spectrum of the product of the interaction of limonene with elemental sulfur.
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Figure 4. MALDI-TOF mass spectrum of the product of the interaction of elemental sulfur with limonene in the region 280–400 m/z, recorded in reflector mode with cation detection.
Figure 4. MALDI-TOF mass spectrum of the product of the interaction of elemental sulfur with limonene in the region 280–400 m/z, recorded in reflector mode with cation detection.
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Figure 5. Oxidative dehydrogenation of limonene with elemental sulfur followed by a Diels–Alder reaction cascade, possible fragmentation products of compound (VI) under MALDI-TOF mass spectral recording conditions, and some putative structures in the macromolecular chain.
Figure 5. Oxidative dehydrogenation of limonene with elemental sulfur followed by a Diels–Alder reaction cascade, possible fragmentation products of compound (VI) under MALDI-TOF mass spectral recording conditions, and some putative structures in the macromolecular chain.
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Figure 6. 13C NMR (A) and 1H NMR (B) spectra of the product of the reaction of limonene with elemental sulfur.
Figure 6. 13C NMR (A) and 1H NMR (B) spectra of the product of the reaction of limonene with elemental sulfur.
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Figure 7. MALDI-TOF mass spectrum of the product of the reaction of elemental sulfur with limonene recorded in reflector mode with anion detection.
Figure 7. MALDI-TOF mass spectrum of the product of the reaction of elemental sulfur with limonene recorded in reflector mode with anion detection.
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Figure 8. Scheme of fragmentation of products of inverse vulcanization of limonene under laser desorption/ionization conditions.
Figure 8. Scheme of fragmentation of products of inverse vulcanization of limonene under laser desorption/ionization conditions.
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Figure 9. Dependence of the number of moles of unreacted sulfur ( n e x S ) on the molar ratio of elemental sulfur and limonene ( n ( S ) n ( L i m o n e n e ) ).
Figure 9. Dependence of the number of moles of unreacted sulfur ( n e x S ) on the molar ratio of elemental sulfur and limonene ( n ( S ) n ( L i m o n e n e ) ).
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Table 1. Amounts of initial cyclooctasulfur, limonene, remaining unreacted sulfur, and covalently bound sulfur under inverse vulcanization conditions.
Table 1. Amounts of initial cyclooctasulfur, limonene, remaining unreacted sulfur, and covalently bound sulfur under inverse vulcanization conditions.
Mass Ratio of Initial Limonene: Sm (Initial S), gm (Initial Limonene), gm (S in the Residue), gm (S Covalently Incorporated in the Polymer), g
1:63.00.50.9052.095
1:84.00.52.0631.937
1:105.00.52.9862.014
1:126.00.54.0021.998
1:147.00.55.0441.956
1:168.00.55.9172.083
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Tarasova, N.; Krivoborodov, E.; Kirakosian, D.; Zanin, A.; Toropygin, I.; Mezhuev, Y. MALDI-TOF Mass Spectrometry as the Tool for the Identification of Features of Polymers Obtained by Inverse Vulcanization. Macromol 2024, 4, 856-870. https://doi.org/10.3390/macromol4040050

AMA Style

Tarasova N, Krivoborodov E, Kirakosian D, Zanin A, Toropygin I, Mezhuev Y. MALDI-TOF Mass Spectrometry as the Tool for the Identification of Features of Polymers Obtained by Inverse Vulcanization. Macromol. 2024; 4(4):856-870. https://doi.org/10.3390/macromol4040050

Chicago/Turabian Style

Tarasova, Natalia, Efrem Krivoborodov, Diana Kirakosian, Alexey Zanin, Ilya Toropygin, and Yaroslav Mezhuev. 2024. "MALDI-TOF Mass Spectrometry as the Tool for the Identification of Features of Polymers Obtained by Inverse Vulcanization" Macromol 4, no. 4: 856-870. https://doi.org/10.3390/macromol4040050

APA Style

Tarasova, N., Krivoborodov, E., Kirakosian, D., Zanin, A., Toropygin, I., & Mezhuev, Y. (2024). MALDI-TOF Mass Spectrometry as the Tool for the Identification of Features of Polymers Obtained by Inverse Vulcanization. Macromol, 4(4), 856-870. https://doi.org/10.3390/macromol4040050

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