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Article

Synthesis of Tosyl- and Nosyl-Ended Polyisobutylenes with High Extent of Functionalities: The Effect of Reaction Conditions

by
Balázs Pásztói
1,2,*,
Tobias M. Trötschler
3,4,5,
Ákos Szabó
1,
Györgyi Szarka
1,
Benjamin Kerscher
3,4,
Rolf Mülhaupt
3,4,5,* and
Béla Iván
1,*
1
Polymer Chemistry Research Group, Institute of Materials and Environment Chemistry, Research Centre for Natural Sciences, Magyar tudósok körútja 2, H-1117 Budapest, Hungary
2
George Hevesy PhD School of Chemistry, Institute of Chemistry, Faculty of Science, Eötvös Loránd University, Pázmány Péter sétány 2, H-1117 Budapest, Hungary
3
Institute for Macromolecular Chemistry, University of Freiburg, Stefan-Meier-Str. 31, D-79104 Freiburg, Germany
4
Freiburg Materials Research Center, University of Freiburg, Stefan-Meier-Str. 21, D-79104 Freiburg, Germany
5
Freiburg Center for Interactive Materials and Bioinspired Technologies (FIT), University of Freiburg, Georges-Köhler-Allee 105, D-79110 Freiburg, Germany
*
Authors to whom correspondence should be addressed.
Polymers 2020, 12(11), 2504; https://doi.org/10.3390/polym12112504
Submission received: 7 October 2020 / Revised: 21 October 2020 / Accepted: 24 October 2020 / Published: 28 October 2020
(This article belongs to the Section Polymer Chemistry)
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Versions Notes

Abstract

:
Endfunctional polymers possess significant industrial and scientific importance. Sulfonyl endgroups, such as tosyl and nosyl endfunctionalities, due their ease of substitution are highly desired for a variety of polymer structures. The sulfonylation of hydroxyl-terminated polyisobutylene (PIB-OH), a chemically and thermally stable, biocompatible, fully saturated polymer, with tosyl chloride (TsCl) and nosyl chloride (NsCl) is presented in this study. PIB-OHs derived from commercial exo-olefin-ended PIB (PIBexo-OH) and allyl-terminated polymer made via quasiliving carbocationic polymerization of isobutylene (PIBall-OH) were tosylated and nosylated in the presence of 4-dimethylaminopyridine (DMAP), pyridine and 1-methylimidazole (1-MI) catalysts and triethylamine (TEA). Our systematic investigations revealed that the end product distribution strongly depends on the relative amount of the components, especially that of TEA. While PIBexo-OTs with quantitative endfunctionality is readily formed from PIBexo-OH, its nosylation is not as straightforward. During sulfonylation of PIBall-OH, the formed tosyl and nosyl endgroups are easily substituted with chloride ions, formed in the first step of sulfonylation, leading to chloride termini. We found that decreased amounts of TEA afford the synthesis of PIBall-OTs and PIBall-ONs with higher than 90% endfunctionalities. These sulfonyl-ended PIBs open new ways for utilizing PIB in various fields and in the synthesis of novel PIB-containing macromolecular architectures.

Graphical Abstract

1. Introduction

Functional polymers with terminal and or pendant functionalities have significant industrial and scientific importance, and as a consequence, intensive research and developments have been taking place with such polymers worldwide. Among these macromolecular materials, functional polyisobutylenes (PIBs) have gained remarkable interest in the last couple of years (see e.g., Refs. 1-30 and references therein). This is mainly due to the demands to increase the average endfunctionality by either conventional or quasiliving carbocationic polymerizations, or to the utilization of functional PIBs as building blocks in a variety of new materials with advanced application possibilities. PIB has a fully saturated, chemically inert backbone with low glass transition temperature, high thermal and oxidative stability, outstanding barrier properties, etc. Based on these attractive features, functional PIBs and its copolymers have already gained broad fields of applications, e.g., starting material of butyl rubbers, oil, fuel and lubricant additives, sealants, adhesives, insulating materials, and the component of biomedical devices on the basis of its biocompatibility.
In spite of the availability of PIBs with a wide range of endfunctionalities [1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28,29,30,31,32,33,34,35,36], a reliable process for certain highly desired endfunctional PIBs with high extents of reactive chain end functionalities, for instance, organosulfonates, such as tosyl- or nosyl-ended PIBs, are still lacking. The most convenient way to obtain PIB-sulfonates is the sulfonylation of hydroxyl-terminated PIBs (PIB-OHs) by the corresponding sulfonyl chlorides, e.g., tosyl chloride (TsCl) or nosyl chloride (NsCl) as shown in Scheme 1. PIB-OHs are usually prepared by hydroboration/oxidation of olefin-terminated PIBs [31,32]. While commercial PIBs with relatively broad molecular weight distributions (MWD) have about 80% reactive exo-olefin functionality [1,4,5,6,8,9] (PIB-Exo), the inifer method [33] and quasiliving carbocationic polymerization (QLCCP) results in PIB-Exo with quantitative vinylidene endgroups [34,35]. In situ allylation by endquenching of QLCCP of isobutylene with allyltrimethylsilane yields PIBs directly with allyl termini (PIB-All) [32]. It has to be noted that significant efforts have been made to increase the exo-olefin functionality in PIB-Exo by conventional carbocationic polymerization in recent years [1,4,5,6,9,24,25,26,27,28,29]. Both PIB-Exo and PIB-All were converted to PIB-OHs [31,32,36], which in principle can be converted to PIB-sulfonates, e.g., tosylates, nosylates and mesylates. The interest in such PIBs is based on the fact that alkyl tosylates are among the most versatile compounds for substitution reactions because the tosyl group is an excellent leaving group. As widely accepted, tosylates can be prepared by the reaction of tosyl chloride and an alcohol. Typically, bases promote this process by capturing the generated HCl during the reaction. Catalysts, such as 4-dialkylaminopyridines, like 4-dimethylaminopyridine (DMAP) and tertiary amines, e.g., triethylamine (TEA), proved to be effective for a wide range of species [37,38,39]. Furthermore, imidazole-based sulfonylation was also described [40,41]. Although these catalysts are efficient in tosylation of alcohols of low molecular weights in most cases, undesired side reactions were observed for some species and under certain reaction conditions. Mostly, the formed tosyl group is substituted by the chloride anion yielding chloride functional group [39,42]. While tosylates are preferred in organic reactions and have a quite extensive literature background, nosylates, despite their even better synthetic features in substitution reactions [43,44,45], have not been explored intensively so far. Based on these characteristics of tosylates and nosylates, effective tosylation/nosylation of PIB-OHs is expected to lead to PIBs with tosyl and nosyl endfunctionalities. These can be utilized in a wide range of subsequent substitution reactions and thus in the preparation of a variety of new macromolecular materials. It has to be mentioned that tosylates and nosylates can also be applied as macroinitiators, e.g., for quasiliving ring-opening polymerization of oxazolines [46]. Consequently, PIBs with tosyl or nosyl chain ends would provide unique opportunities to prepare an array of novel macromolecular materials.
Based on the current literature, very limited knowledge exists on PIBs with sulfonate (tosylate, nosylate, mesylate) endgroups. In an early attempt, linear and three-arm star PIB-OHs were tosylated with excess TsCl in the presence of DMAP and TEA as bases in dichloromethane (DCM) [47]. Although complete consumption of the hydroxyl groups was claimed, detailed analysis of the products was not carried out. However, it was found that using these tosylated PIBs as macroinitiators for the quasiliving cationic ring-opening polymerization (CROP) of 2-methyl-2-oxazoline resulted only in 70–80% blocking efficiency, indicating incomplete initiation of the CROP process by the chain ends, which might be an indication of incomplete tosylation. As found by us recently [48] and during our preliminary experiments, lower than quantitative endfunctionalization was achieved by reacting TsCl with PIB-OH under similar conditions as reported [47]. Converting the hydroxyl group of PIB-OH prepared from industrial PIB-Exo by methanesulfonyl chloride (mesyl chloride, MsCl) led to mesylated PIB, which was used as an intermediate for polyisobutylene supported catalyst systems [49,50]. However, detailed analysis of this process and the resulting polymers or the average endfunctionality has not been reported in the case of these sulfonylations.
Herein, we report on our systematic investigations aiming at to determine the effect of reaction conditions on the efficiency of tosylation and nosylation of PIB-OHs derived from commercially available PIB-Exo and laboratory PIB-All prepared by QLCCP. Our definite goal was to reveal the reaction parameters which result in high tosylation and nosylation yields, i.e., high tosyl and nosyl endfunctionalities. Thorough experiments were also carried out on the influence of the origin of the PIB-OH, i.e., PIBexo-OH or PIBall-OH, the ratio of the reagents and the reaction times on the endfunctionalities of the sulfonylated PIBs.

2. Materials and Methods

2.1. Materials

Dichloromethane (DCM, 99.9%, Molar Chemicals, Halásztelek, Hungary), tetrahydrofuran (THF, 99.9%, VWR Chemicals, West Chester, PA, USA), benzotrifluoride (BTF, ≥99%, Sigma-Aldrich, St. Louis, MO, USA) and 2-ethyl-2-oxazoline (EtOx, 99+%, Aldrich, St. Louis, MO, USA) were refluxed on CaH2 for a couple of hours and distilled over it under N2 atmosphere freshly before use. Triethylamine (TEA, ≥99.0%, TCI Chemicals, Tokyo, Japan) and 1-methylimidazole (1-MI, ≥99%, Sigma-Aldrich, St. Louis, MO, USA) was distilled under N2 atmosphere freshly before use. Glissopal 1000 (BASF SE, Ludwigshafen, Germany), p-toluenesulfonyl chloride (tosyl chloride, TsCl, ≥99.0%, TCI Chemicals, Tokyo, Japan), p-nitrobenzenesulfonyl chloride (nosyl chloride, NsCl, 97%, Sigma-Aldrich, St. Louis, MO, USA) and 4-dimethylaminopyridine (DMAP, ≥99.9%, Sigma-Aldrich, St. Louis, MO, USA) were used as receive.

2.2. Characterization

NMR spectroscopy. 1H NMR spectra of all endfunctional PIBs were recorded on a Varian 500 MHz spectrometer. All measurements were performed in CDCl3 as solvent and at 30 °C. For spectra calibration of the 1H NMR spectra, the chloroform peak was set to 7.26 ppm.
Gelpermeation chromatography (GPC). The GPC equipment was composed of a Waters 515 HPLC pump, Waters Styragel column set with three columns (HR1, HR2, HR4), and it was equipped with an Aligent 390 RI detector. THF was used as mobile phase with a flow rate of 1 mL/min. The average molar masses and the polydispersity (Mw/Mn), were determined by the use of a calibration made with narrow MWD polystyrene standards in the molecular weight range of 104 to 6 × 105 Da.

2.3. Synthesis of PIB-All

A solution of 2-chloro-2,4,4-trimethylpentane (TMPCl, 4.1 g, 0.03 mol) in n-hexane (1520 mL) and DCM (1240 mL) was cooled down in a dry ice-isopropanol mixture to −78 °C. To this reaction solution, under continuous stirring, tetramethylethylenediamine (TMEDA, 4.1 mL, 3.2 g, 0.03 mol, 1.0 eq.) was given. Afterward, TiCl4 (18.2 mL, 31.4 g, 0.17 mol, 6.0 eq.) and isobutylene (IB, 32.6 mL, 23.5 g, 0.42 mol, 15.2 eq.) were carefully added and the mixture was stirred at −78 °C for 30 min. After complete conversion of IB, pre-chilled allyltrimethylsilane (ATMS, 8.8 mL, 8.3 g, 0.06 mol, 2 eq.) was given and the solution was stirred for 30 min. Finally, the reaction was stopped with the addition of cold MeOH (200 mL). The mixture was warmed up to room temperature, which resulted a two-phase mixture (including a higher phase of n-hexane and a lower phase of DCM/MeOH). The n-hexane phase was separated and washed with a solution of NaHCO3 in H2O (250 mL) three times, dried over MgSO4 overnight and cleaned up via filtering. The solvent was removed under reduced pressure and the product was dried under vacuum at 60 °C until constant weight. PIB-All was obtained as a colourless, clean, viscous liquid (yield: 22.4 g, 81%). 1H NMR (500 MHz, CDCl3, 30 °C): δ = 0.76–1.80 (m, 116H), 1.95–2.07 (d, 2H), 4.92-5.07 (m, 2H), 5.77-5.93 (m, 1H) ppm. GPC: Mn = 820 g/mol, D = 1.16).

2.4. Synthesis of PIBall-OH

PIB-All (7.0 g, 7.78 mmol) was dissolved in dry THF (35 mL) under nitrogen atmosphere. Afterwards, 0.5 M solution of 9-borabicyclo[3.3.1]nonane in THF (9-BBN, 0.5 M, 78 mL, 0.039 mol, 5 eq.) was added dropwise and the mixture was stirred for 5 h at room temperature. Into this mixture, KOH (6.5 g, 0.12 mol, 15 eq.) in MeOH solution (43 mL) was carefully added, then the reaction mixture was cooled down with an ice bath, and aqueous H2O2 (30%, 13.2 mL, 4.0 g, 0.12 mol, 15 eq.) was dropped under constant stirring. The reaction mixture was stirred overnight at room temperature. After this, n-hexane (70 mL) and H2O (20 mL) were added, and the organic phase of the two-phase mixture was separated, washed with a solution of NaHCO3 in H2O (20 mL) three times, dried over MgSO4 overnight and cleaned up via filtering. The solvent was removed under reduced pressure and the product was dried under vacuum at 60 °C until constant weight. PIBall-OH was obtained as a colourless, clean, viscous liquid (yield: 6.9 g, 99%). 1H NMR (500 MHz, CDCl3, 30 °C): δ = 0.78–1.91 (m, 130H), 3.55–3.68 (t, 2H). GPC: Mn = 1160 g/mol, D = 1.18.

2.5. Synthesis of PIBexo-OH

PIB-Exo (50.0 g, 50.0 mmol) was dissolved in dry THF (250 mL) under nitrogen atmosphere. Afterward, 0.5 M solution of 9-borabicyclo[3.3.1]nonane in THF (9-BBN, 0.5 M, 500 mL, 0.250 mol, 5 eq.) was added dropwise and the mixture was stirred for 4 h at room temperature. Into this mixture, KOH (70.1 g, 1.25 mol, 25 eq.) in MeOH solution (440 mL) was carefully added, then the reaction mixture was cooled down with an ice bath, and aqueous H2O2 (30%, 29.3 mL, 42.5 g, 1.25 mol, 25 eq.) was dropped under constant stirring. The reaction mixture was stirred overnight at room temperature. After this, n-hexane (250 mL) and H2O (100 mL) were added, and the organic phase of the two-phase mixture was separated, washed with a solution of NaHCO3 in H2O (100 mL) three times, dried over MgSO4 overnight and cleaned up via filtering. The solvent was removed under reduced pressure and the product was dried under vacuum at 60 °C until constant weight. The final product was resulted after precipitation from THF to tenfold excess of MeOH. PIBexo-OH was obtained as a colorless, clean, viscous liquid (yield: 43.6 g, 86%). 1H NMR (500 MHz, CDCl3, 30 °C): δ = 0.88–1.80 (m, 216H), 3.26–3.53 (m, 2H), 4.77–4.86 (*coupled, m, 1H), 5.09–5.19 (*endo, m, 1H). GPC: Mn = 1360 g/mol, D = 1.53.

2.6. Experiments on the Tosylation of PIBexo-OH and PIBall-OH

0.1 g or 0.2 g of PIB-OH was dissolved in dry DCM and the solution was added to a previously heat-dried small glass vial equipped with a magnetic stirrer. The vial was carefully closed with a septum cap and nitrogen was transferred through solution for several minutes. Afterwards, calculated amount of TEA and the catalyst (DMAP or 1-methylimidazole in DCM solution) were added with constant stirring. Finally, tosyl chloride in DCM solution was given dropwise to the reaction mixture. Reaction was conducted at room temperature; samples were withdrawn at defined times and precipitated into large excess of MeOH. Polymer was isolated, washed with MeOH and dried under vacuum at 40 °C until constant weight. Dry product was analyzed by 1H NMR spectroscopy to determine the conversion of hydroxyl endgroup.

2.7. Experiments on the Nosylation of PIBexo-OH and PIBall-OH

0.1 g or 0.2 g of PIB-OH was dissolved in dry THF and the solution was added to a previously heat-dried small glass vial equipped with a magnetic stirrer. The vial was carefully closed with a septum cap, and nitrogen was transferred through solution for several minutes. Afterward, calculated amount of TEA and the catalyst (DMAP or 1-methylimidazole in THF solution) were added with constant stirring. Finally, nosyl chloride in THF solution was given dropwise to the reaction mixture. Reaction was conducted at room temperature; samples were withdrawn at defined times and precipitated into large excess of MeOH. Polymer was isolated, washed with MeOH and dried under vacuum at 40 °C until constant weight. The dry product was analyzed by 1H NMR spectroscopy to determine the conversion of the hydroxyl endgroup.

2.8. Synthesis of PIBall-OTs

PIBall-OH (37.0 g, 30.8 mmol) was dissolved in dry DCM (370 mL) under nitrogen atmosphere. Afterwards, TEA (21.5 mL, 15.6 g, 0.15 mol, 5 eq.) and 1-methylimidazole (4.9 mL, 5.1 g, 62 mmol, 2 eq.) were added under continuous stirring. After complete dissolution of the reagents, tosyl chloride (58.8 g, 0.31 mol, 10 eq.) in DCM solution was dropped into the reaction mixture carefully while cooled down with an ice-bath. The reaction content was warmed up to room temperature and stirred overnight. After the addition of MeOH (50 mL), the mixture was stirred for 30 min, concentrated and precipitated into tenfold excess of MeOH (2000 mL). Raw product was isolated, washed with MeOH (100 mL) several times, dried under vacuum at 60 °C. Then it was resolved in n-hexane (150 mL), filtered if necessary, precipitated again into tenfold excess of MeOH (1500 mL), the product was isolated, washed with MeOH (100 mL) several times and dried under vacuum at 60 °C until constant weight. Precipitation procedure was usually conducted three times, but until the dry product was completely clear and lost the initial yellowish colour. PIBall-OTs was obtained as a colourless, clean, viscous liquid (yield: 36.7 g, 88%). 1H NMR (500 MHz, CDCl3, 30 °C): δ = 0.65–1.68 (m, 192H), 2.39–2.50 (s, 3H), 3.92–4.07 (t, 2H), 7.31–7.38 (d, 2H), 7.73–7.87 (d, 2H) ppm. GPC: Mn = 1480 g/mol, D = 1.16.

2.9. Synthesis of PIBall-ONs

PIBall-OH (3.45 g, 3.45 mmol) was dissolved in dry THF (50 mL) under nitrogen atmosphere. Afterwards, TEA (2.4 mL, 1.7 g, 0.017 mol, 5 eq.) and 1-methylimidazole (0.55 mL, 0.67 g, 6.9 mmol, 2 eq.) were added under continuous stirring. After complete dissolution of the reagents, nosyl chloride (7.65 g, 0.035 mol, 10 eq.) in THF solution was dropped into the reaction mixture carefully while cooled down with an ice-bath. The reaction content was warmed up to room temperature and stirred overnight. After the addition of MeOH (10 mL), the mixture was stirred for 30 min, concentrated and precipitated into tenfold excess of MeOH (500 mL). Raw product was isolated, washed with MeOH (20 mL) several times, dried under vacuum at 60 °C. Then it was resolved in n-hexane (35 mL), filtered if necessary, precipitated again into tenfold excess of MeOH (350 mL), the product was isolated, washed with MeOH (20 mL) several times and dried under vacuum at 60 °C until constant weight. The precipitation procedure was usually conducted three times until the dry product was completely clear. PIBall-ONs was obtained as a slightly yellow, clean, viscous liquid (yield: 1.55 g, 45%). 1H NMR (500 MHz, CDCl3, 30 °C): δ = 0.78–1.86 (m, 147H), 3.46–3.53 (*PIB-Cl, t, 2H), 4.07–4.16 (t, 2H), 8.07–8.18 (d, 2H), 8.36–8.45 (d, 2H) ppm. GPC: Mn = 1310 g/mol, D = 1.11.

3. Results and Discussion

In order to study the effect of the chain end structure on tosylation and nosylation, both exo-olefin- and allyl-ended PIBs were used as starting materials. Because the exo-olefin-teminated polymer (PIB-Exo) is a commercially available inexpensive product, and used widely for research purposes as well (see e.g., references 48–50 and references therein), we selected this polymer as one of the starting materials for our studies. As displayed in Figure 1, the commercial PIB-Exo, obtained by utilizing the chain transfer process in conventional carbocationic polymerization of isobutylene, contains not only exo-, but endo- and in-chain olefins as well (see also Figure S1 in the Supporting Information). Considering these double bonds, PIB-Exo has 81% exo-olefin functionality and Mn of 1200 g/mol by 1H NMR spectroscopy (Mn = 1150 g/mol and Mw/Mn = 1.61 by GPC). The allyl-terminated polyisobutylene (PIB-All) used in this work was obtained by quasiliving carbocationic polymerization of isobutylene and in-situ quenching by ATMS [32]. This polymer has 100% allyl functionality according to the 1H NMR spectrum of this polymer (Figure 1 and Figure S2), and Mn of 820 g/mol and Mw/Mn of 1.16. The reaction routes for obtaining hydroxyl-ended PIBs from these olefin-terminated polymers are depicted in Scheme 1. As expected, hydroboration/oxidation with 9-BBN [31] converts only the exo-olefin in PIB-Exo to hydroxyl groups as indicated in Figure 2 and Figure S4. The endo-olefin and in-chain double bonds do not react due to steric hindrance. The allyl endgroup is fully transformed to hydroxyl group as shown in Figure 3 and Figure S3. The resulting hydroxyl-ended PIBs, that is PIBexo-OH and PIBall-OH, react with tosyl chloride (TsCl) and nosyl chloride (NsCl) as displayed in Scheme 1 under various reaction conditions. All reactions were carried out under dry atmosphere at room temperature.
The first attempts on tosylation of PIBexo-OH were carried out to reproduce previously described experiments [47] by applying the same reaction conditions (DCM solvent, 2 eq. of TsCl, 2 eq. of DMAP, 13.7 eq. of TEA, room temperature, 10 h reaction time). However, surprisingly these conditions did not lead to full conversion of the PIBexo-OH. Therefore we tried also pyridine instead of DMAP, different TsCl concentrations and various reactions times (Entry 1–3 in Table 1). As shown in Table 1, pyridine alone is not sufficiently effective catalyst of tosylation, leading only to 16% conversion. As the data indicate in Table 1 and in Figure 2, tenfold excess of TsCl in the presence of 2 eq. DMAP and 10 eq. TEA leads to complete transformation of the hydroxyl groups in PIBexo-OH to PIB with tosyl endgroups (PIBexo-OTs), even with relatively short reaction time of 7 h (Entry 5 in Table 1). This reaction time is sufficient to reach only 80% conversion during nosylation under the otherwise same condition, but using THF as solvent, as shown in Table 2 (Entry 11). Because the nosyl chloride has limited solubility in DCM, all nosylation reactions were carried out in THF, which is an appropriate solvent for both NsCl and PIB. Longer reaction times of nosylation of PIBexo-OH lead to ~90% conversion, i.e., to the formation of nosyl ended polymers (PIBexo-ONs) as indicated by the 1H NMR spectrum in Figure 2.
The results of the experiments on the sulfonylation of PIBexo-OH indicated that 10 eq. of the alkyl sulfonyl chloride with the combination of 2 eq. DMAP and 10 eq. TEA results in complete transformation of the hydroxyl group for tosylation and nearly complete conversion for nosylation. Because the PIB-Exo has an extra methyl group connected to the chain terminus compared to the lack of such substituent in the allyl endgroup of PIB-All, it was expected that the latter one has higher reactivity than PIBexo-OH. However, using smaller excess of tosyl chloride, that is, only 2–5 eq., for the tosylation of PIBall-OH resulted in only partial conversion even with longer reaction times as shown in Table 3 (Entry 15–18), on the one hand. On the other hand, alkyl chloride chain end appeared at long reaction times (72 h). Thus, experiments with tenfold excess of TsCl reagent were carried out by using the same reaction conditions as for PIBexo-OH with reaction times from 4.5 h to 72 h (Entry 19–24 in Table 3). These experiments led to interesting results. First, the transformation of the alcohol chain end is much faster with PIBall-OH, i.e., the reactivity of PIBall-OH is higher than that of PIBexo-OH with TsCl as expected. Second, not only tosyl endgroups but PIBs bearing a terminal primary chlorine group (PIBall-Cl) as side products were also observed as indicated by the signal at 3.50 ppm in the 1H NMR spectra which is assigned to the methylene group next to the chlorine termini (Figure 3). Furthermore, the amount of PIBall-Cl is increasing, while the amount of tosylated PIB is decreasing with the reaction time as shown in Table 3 (Entry 19–24) and in Figure 4. Therefore, the occurrence of the following processes can be considered to take place according to results with low MW compounds [39] under the applied conditions as depicted in Scheme 2: (1) the initial reaction of the alkyl sulfonyl chloride with the alcohol yields the main tosylated product, (2) meanwhile the HCl byproduct forms triethylammonium hydrochloride (TEA*HCl) with TEA, in which the chloride ion has a sufficient nucleophilicity to displace the alkyl sulfonyl group. As a consequence, as can be seen in Scheme 2, the first substitution step, i.e., tosylation, is followed by substituting the tosyl group, which is a good leaving group, with chlorine.
Experiments with lower than 10 eq. TEA were also carried out. It was found that although 2 eq. TEA results in 5% chloride endgroup (Entry 25), which is much smaller than that obtained with 10 eq. (Entry 20 in Table 3) at similar reaction time. However, only 53% of the hydroxyl group is consumed in this reaction (Entry 25 in Table 3). Increasing the amount of TEA to 3 eq. and 5 eq. leads to complete conversion of the hydroxyl groups and nearly 90% tosylate functionality is observed with 5 eq. of TEA in 20 h reaction time. Summarizing the results of tosylation of PIBall-OH with TsCl obtained with DMAP catalyst in the presence of TEA in the range of 5–10 eq. it can be claimed that with 10 eq. TsCl PIB-tosylates with around 90% tosyl functionalities and ~10% of PIBall-Cl can be prepared. As reported in the literature [40], not only DMAP but 1-methylimidazole (1-MI) is also an efficient catalyst of acylation of alcohols. Therefore, attempts were made by us to investigate the effect of 1-MI on the tosylation reaction of PIBall-OH by still keeping the amount of TEA at relatively low levels as shown in Table 3. As indicated by the results of Entry 30–34, 2 eq. TEA is insufficient to reach high tosylation yields, but with 3 eq. and 5 eq. of TEA, the consumption of the hydroxyl groups is complete, the undesired side reaction of chlorination is suppressed to 3–8%, and thus PIBall-tosylates with 92–97% tosylate endfunctionalities are obtained as confirmed by the 1H NMR spectrum in Figure 3. These optimal reaction conditions by using 1-MI as catalyst of tosylation of PIBall-OH provide an efficient tool to prepare tosylate-ended PIBs with high, nearly quantitative endfunctionalities. Due to the fact that the PIB-All prepolymer with narrow MWD is synthesized by quasiliving carbocationic polymerization of isobutylene, well-defined PIBall-OTs also with narrow MWD can be obtained by this process. Thus, the resulting PIBall-OTs can be utilized in various further derivatization reactions and as a starting material for macromolecular assemblies of complex architectures.
The effect of the reaction conditions on the nosylation of PIBall-OH was also investigated. As shown in Table 4, the consumption of the terminal hydroxyl groups is complete in the presence of 10 eq. NsCl, 2 eq. DMAP and 10 eq. TEA after 4 h reaction time (Entry 35–39). However, with this and longer reaction times from 14% to 30% chlorine endgroups are also present in the resulting polymers. Decreasing the amount of TEA to 2 eq. gives only 14% nosylation conversion in 19 h. Using reduced amounts of TEA of 3 eq. and 5 eq. results in complete hydroxyl consumption, and in the case of 5 eq. TEA 91% and 93% nosyl endfunctionalities are observed (Entry 45 and 46 in Table 4). With 1-MI as catalyst, PIBall-ONs with 89–94% nosyl endfunctionalities are formed as the 1H NMR spectra and the data in Table 4 indicate (Figure 3). In these cases, negligible amounts of 2–5% PIBall-ONs with unreacted hydroxyl termini can also be observed, and the chlorine endfunctionalities fall in the region of 4–8%. These results show that PIBall-ONs with higher than 90% nosyl functionalities can be obtained with either DMAP or 1-MI catalyst by using 5 eq. of TEA and proper reaction times. Based on the reactivity of the nosyl group, these novel nosyl-ended PIBs, unpublished so far in the open literature according to the best of our knowledge, are expected to open new ways for the preparation of various PIB-based polymer architectures.

4. Conclusions

Tosylation and nosylation of hydroxyl-ended polyisobutylenes (PIB-OHs) derived from a commercially available exo-olefin-terminated polymer (PIBexo-OH) and from allyl-ended macromolecules (PIBall-OH), prepared by quasiliving carbocationic polymerization of isobutylene, were systematically investigated. A thorough exploration was conducted to reveal the influence of the ratios of the reagents, such as 4-dimethylaminopyridine (DMAP), pyridine, 1-methylimidazole (1-MI), and trimethylamine (TEA), and reaction time on the conversion of the hydroxyl termini in these PIB-OHs. A significant difference in the reactivity between the two hydroxyl-terminated polymers was found, i.e., the PIBall-OH reacts faster with the sulfonyl chlorides than the PIBexo-OH, presumably because of steric reasons. While quantitative tosylation was achieved with PIBexo-OH, nosylation led to PIBexo-ONs with functionality of ~90%. Unexpectedly, it was found that the tosyl endgroup reacts further with the chloride ion formed during tosylation, and chlorine-ended PIB (PIBall-Cl) is formed. The conversion of the hydroxyl group and the relative amount of the sulfonyl and chlorine termini strongly depend on TEA and reaction times. Decreased amounts of TEA in the range of 3–5 eq. and optimal reaction times lead to PIBall-OTs and PIBall-ONs with higher than 90% sulfonyl functionalities. The resulting tosyl- and nosyl-ended PIBs are capable of subsequent derivatizations, and thus various novel endfunctional PIBs can be obtained via substitution reactions. This enables the preparation of an array of PIB-containing new macromolecular architectures not existed before.

Supplementary Materials

The following are available online at https://www.mdpi.com/2073-4360/12/11/2504/s1, Figure S1: 1H NMR spectrum of the PIB-Exo sample with integral values; Figure S2: 1H NMR spectrum of the PIB-All sample with integral values; Figure S3: 1H NMR spectrum of the PIBall-OH sample with integral values; Figure S4: 1H NMR spectrum of the PIBexo-OH sample with integral values; Figure S5: 1H NMR spectrum of the PIBall-OTs sample with integral values; Figure S6: 1H NMR spectrum of the PIBall-ONs sample with integral values; Figure S7: GPC curves of the synthesized PIBall-OTs macroinitiator and its starting material PIBall-OH; Figure S8: GPC curves of the synthesized PIBall-ONs macroinitiator and its starting material PIBall-OH.

Author Contributions

All authors designed and contributed to this study. Conceptualization, B.P., T.M.T., Á.S., G.S., B.K., R.M., B.I.; Methodology, B.P., T.M.T., Á.S., G.S., B.K., B.I.; Analysis, B.P., T.M.T., Á.S., G.S., B.K.; Data evaluation, B.P., T.M.T., Á.S., G.S., B.K., R.M., B.I.; Writing—Draft Preparation, B.P., T.M.T., Á.S., G.S., B.K., B.I.; Writing—Review & Editing, B.P., T.M.T., Á.S., G.S., B.K., R.M., B.I.; Supervision, R.M., B.I.; Funding Acquisition, R.M., B.I.; All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by the National Research, Development and Innovation Office (NRDIO), Hungary (NN116252, NN129366, K135946), and the German Research Foundation (DFG; MU 836/13-1, 269965048) in the framework of the European Research Area Chemistry (ERA-Chemistry) and the NRDIO’s international cooperation programs.

Acknowledgments

The authors gratefully acknowledge the support by the European Research Area Chemistry (ERA-Chemistry) program, the National Research, Development and Innovation Office, Hungary (NN116252, NN129366, K135946) and the German Research Foundation (DFG; MU 836/13-1, 269965048).

Conflicts of Interest

The authors declare no conflict of interest.

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Polymers 12 02504 sch001 550
Scheme 1. The synthesis routes for the preparation of tosyl- and nosyl-ended polyisobutylenes derived from exo-olefin-ended (PIB-Exo) and allyl-terminated (PIB-All) polymers (PIB-All was obtained by quasiliving carbocationic polymerization).
Scheme 1. The synthesis routes for the preparation of tosyl- and nosyl-ended polyisobutylenes derived from exo-olefin-ended (PIB-Exo) and allyl-terminated (PIB-All) polymers (PIB-All was obtained by quasiliving carbocationic polymerization).
Polymers 12 02504 sch001
Polymers 12 02504 g001 550
Figure 1. 1H NMR spectra of the exo-olefin-ended (a) and allyl-terminated polyisobutylene (b).
Figure 1. 1H NMR spectra of the exo-olefin-ended (a) and allyl-terminated polyisobutylene (b).
Polymers 12 02504 g001
Polymers 12 02504 g002 550
Figure 2. 1H NMR spectra of PIBexo-OH (a), PIBexo-OTs (b) and PIBexo-ONs (c).
Figure 2. 1H NMR spectra of PIBexo-OH (a), PIBexo-OTs (b) and PIBexo-ONs (c).
Polymers 12 02504 g002
Polymers 12 02504 sch002 550
Scheme 2. Tosylation/nosylation of hydroxyl-ended polyisobutylene (PIBall-OH) and subsequent chlorination leading to primary chloride endfunctional polyisobutylene.
Scheme 2. Tosylation/nosylation of hydroxyl-ended polyisobutylene (PIBall-OH) and subsequent chlorination leading to primary chloride endfunctional polyisobutylene.
Polymers 12 02504 sch002
Polymers 12 02504 g003 550
Figure 3. 1H NMR spectra of PIBall-OH (a), PIBall-OTs (b), PIBall-ONs (c) and PIBall-Cl (d).
Figure 3. 1H NMR spectra of PIBall-OH (a), PIBall-OTs (b), PIBall-ONs (c) and PIBall-Cl (d).
Polymers 12 02504 g003
Polymers 12 02504 g004 550
Figure 4. Tosylate and chloride endgroup functionalities as a function of the reaction time of the tosylation of PIBall-OH (Entry 19–24 in Table 3; the lines are drawn only for directing the eye).
Figure 4. Tosylate and chloride endgroup functionalities as a function of the reaction time of the tosylation of PIBall-OH (Entry 19–24 in Table 3; the lines are drawn only for directing the eye).
Polymers 12 02504 g004
Table
Table 1. The effect of the reaction conditions on the tosylation of PIBexo-OH at room temperature.
Table 1. The effect of the reaction conditions on the tosylation of PIBexo-OH at room temperature.
EntrySolventt (h)TsCl (eq.)Catalyst (eq.)TEA (eq.)-OH (%)-OTs (%)
1DCM241.254 (pyridine)08416
2DCM481.254 (pyridine)08416
3DCM721.254 (pyridine)08416
4DCM2452 (DMAP)102575
5DCM7102 (DMAP)100100
6DCM22102 (DMAP)100100
7DCM24102 (DMAP)100100
8DCM29102 (DMAP)100100
9DCM48102 (DMAP)100100
10DCM70102 (DMAP)100100
Table
Table 2. The effect of the reaction conditions on the nosylation of PIBexo-OH at room temperature.
Table 2. The effect of the reaction conditions on the nosylation of PIBexo-OH at room temperature.
EntrySolventt (h)NsCl (eq.)Catalyst (eq.)TEA (eq.)-OH (%)-ONs (%)
11THF7102 (DMAP)102080
12THF22102 (DMAP)101189
13THF29102 (DMAP)101288
14THF70102 (DMAP)101090
Table
Table 3. The effect of the reaction conditions on the tosylation of PIBall-OH at room temperature.
Table 3. The effect of the reaction conditions on the tosylation of PIBall-OH at room temperature.
EntrySolventt (h)TsCl (eq.)Catalyst (eq.)TEA (eq.)–OH (%)–OTs (%)–Cl (%)
15DCM2422 (DMAP)1083170
16DCM7232 (DMAP)10186121
17DCM2452 (DMAP)1033670
18DCM7252 (DMAP)10512920
19DCM4.5102 (DMAP)100937
20DCM22102 (DMAP)1007426
21DCM28102 (DMAP)1006931
22DCM46.5102 (DMAP)1005743
23DCM48102 (DMAP)1005644
24DCM72102 (DMAP)1004654
25DCM19102 (DMAP)247485
26DCM20102 (DMAP)508911
27DCM50102 (DMAP)508119
28DCM20103 (DMAP)308416
29DCM50103 (DMAP)307921
30DCM19102 (1-MI)240582
31DCM20102 (1-MI)50973
32DCM50102 (1-MI)50946
33DCM20103 (1-MI)30973
34DCM50103 (1-MI)30928
Table
Table 4. The effect of the reaction conditions on the nosylation of PIBall-OH at room temperature.
Table 4. The effect of the reaction conditions on the nosylation of PIBall-OH at room temperature.
9Solventt (h)NsCl (eq.)Catalyst (eq.)TEA (eq.)-OH (%)-ONs (%)-Cl (%)
35THF1102 (DMAP)108893
36THF2102 (DMAP)103934
37THF3102 (DMAP)102944
38THF4102 (DMAP)102926
39THF4.5102 (DMAP)1008614
40THF22102 (DMAP)1008218
41THF28102 (DMAP)1008218
42THF46.5102 (DMAP)1008119
43THF72102 (DMAP)1007129
44THF19102 (DMAP)28695
45THF20102 (DMAP)51927
46THF50102 (DMAP)50919
47THF20103 (DMAP)308119
48THF50103 (DMAP)307228
49THF19102 (1-MI)2493813
50THF20102 (1-MI)52944
51THF50102 (1-MI)52908
52THF20103 (1-MI)35914
53THF50103 (1-MI)35896
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Pásztói, B.; Trötschler, T.M.; Szabó, Á.; Szarka, G.; Kerscher, B.; Mülhaupt, R.; Iván, B. Synthesis of Tosyl- and Nosyl-Ended Polyisobutylenes with High Extent of Functionalities: The Effect of Reaction Conditions. Polymers 2020, 12, 2504. https://doi.org/10.3390/polym12112504

AMA Style

Pásztói B, Trötschler TM, Szabó Á, Szarka G, Kerscher B, Mülhaupt R, Iván B. Synthesis of Tosyl- and Nosyl-Ended Polyisobutylenes with High Extent of Functionalities: The Effect of Reaction Conditions. Polymers. 2020; 12(11):2504. https://doi.org/10.3390/polym12112504

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Pásztói, Balázs, Tobias M. Trötschler, Ákos Szabó, Györgyi Szarka, Benjamin Kerscher, Rolf Mülhaupt, and Béla Iván. 2020. "Synthesis of Tosyl- and Nosyl-Ended Polyisobutylenes with High Extent of Functionalities: The Effect of Reaction Conditions" Polymers 12, no. 11: 2504. https://doi.org/10.3390/polym12112504

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