A Study of Isosorbide Synthesis from Sorbitol for Material Applications Using Isosorbide Dimethacrylate for Enhancement of Bio-Based Resins

Citation: Jašek, V.; Fuˇcík, J.; Krhut, J.; Mravcova, L.; Figalla, S.; Pˇrikryl, R. A Study of Isosorbide Synthesis from Sorbitol for Material Applications Using Isosorbide Dimethacrylate for Enhancement of Bio-Based Resins. Polymers 2023,15, 3640. https:// doi.org/10.3390/polym15173640 Academic Editors: Jintao Wan and Hong Fan Received: 10 August 2023 Revised: 29 August 2023 Accepted: 30 August 2023 Published: 4 September 2023 Copyright: © 2023 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). polymers Article A Study of Isosorbide Synthesis from Sorbitol for Material Applications Using Isosorbide Dimethacrylate for Enhancement of Bio-Based Resins Vojtˇech Jašek 1,* , Jan Fuˇcík2, JiˇríKrhut 1,*, Ludmila Mravcova 2, Silvestr Figalla 1and Radek Pˇrikryl 1 1Institute of Materials Chemistry, Faculty of Chemistry, Brno University of Technology, 61200 Brno, Czech Republic; silvestr[email protected] (S.F.); [email protected] (R.P.) 2Institute of Environmental Chemistry, Faculty of Chemistry, Brno University of Technology, 61200 Brno, Czech Republic; [email protected] (J.F.); [email protected] (L.M.) *Correspondence: [email protected] (V.J.); [email protected] (J.K.) Abstract: Bio-based cross-linkers can fulfill the role of enhancing additives in bio-sourced curable materials that do not compare with artificial resin precursors. Isosorbide dimethacrylate (ISDMMA) synthesized from isosorbide (ISD) can serve as a cross-linker from renewable sources. Isosorbide is a bicyclic carbon molecule produced by the reaction modification of sorbitol and the optimal conditions of this reaction were studied in this work. The reaction temperature of 130 ◦ C and 1% w/wamount of para-toluenesulfonic acid (p-TSA) were determined as optimal and resulted in a yield of 81.9%. Isosorbide dimethacrylate was synthesized via nucleophilic substitution with methacrylic anhydride (MAA) with the conversion of 94.1% of anhydride. Formed ISD and ISDMMA were characterized via multiple verification methods (FT-IR, MS, 1 H NMR, and XRD). Differential scanning calorimetry (DSC) proved the curability of ISDMMA (activation energy E a of 146.2 kJ/mol) and the heat-resistant index of ISDMMA (T s reaching value of 168.9) was determined using thermogravimetric analysis (TGA). Characterized ISDMMA was added to the precursor mixture containing methacrylated alkyl 3-hydroxybutyrates (methyl ester M3HBMMA and ethyl ester E3HBMMA), and the mixtures were cured via photo-initiation. The amount of ISDMMA cross-linker increased all measured parameters obtained via dynamic mechanical analysis (DMA), such as storage modulus (E’) and glass transition temperature (T g ), and the calculated cross-linking densities ( νe ). Therefore, the enhancement influence of bio-based ISDMMA on resins from renewable sources was confirmed. Keywords: isosorbide; isosorbide dimethacrylate; PHB; alkyl 3-hydroxybutyrates; enhancement; cross-linker 1. Introduction Isosorbide is a very promising molecule for a vast amount of different applications including medical [ 1 , 2 ], plasticizing [ 3 – 5 ], materials [ 6 , 7 ], or flame retardants [ 8 – 10 ]. This molecule is synthesized and manufactured from various starting substances. When sorbitol (a naturally occurring polyol) is used, a dehydration reaction is required to obtain isosorbide [ 11 , 12 ]. Many synthesis methods, including various catalysts, were introduced, experimentally assessed, and described in the published literature [ 13 – 16 ]. In addition to using sorbitol as a starting material for isosorbide synthesis, various carbohydrate structures, such as glucose [ 17 ] or starch [ 18 – 20 ], are used to manufacture this compound. However, a different approach needs to be used in such cases to obtain high yields of isosorbide. The mentioned starting materials are compounds containing carbonyl functional groups, meaning that they need to be reduced to alcohol (the alcohol formed from the reduced C6 carbonyl structure is sorbitol) [ 21 , 22 ]. After the reduction of carbonyl compounds, the dehydration process occurs, eventually forming isosorbide. Polymers 2023,15, 3640. https://doi.org/10.3390/polym15173640 https://www.mdpi.com/journal/polymers Polymers 2023,15, 3640 2 of 18 Isosorbide dimethacrylate, a diester of isosorbide and methacrylic acid, has a major potential in material applications [ 23 – 25 ]. This compound is synthesized via various reaction approaches such as a direct Fisher esterification involving isosorbide and methacrylic acid with an acidic catalyst [ 26 ]. Methacrylic anhydride can also be used as an appropriate nucleophile in the environment of a suitable base (such as N,N-dimethylaminopyridine (DMAP), or miscible carboxylates) [ 27 – 29 ]. Besides the acid and anhydride, methacryloyl chloride can serve as the most reactive type of nucleophile for this reaction [ 30 ]. Once isosorbide dimethacrylate is formed it can be used, especially as a cross-linking agent for numerous usages requiring curable resins [ 31 ]. It can be involved in 3D printing technologies (e.g., SLA) [ 32 ], as a component in bio-based coatings [ 33 , 34 ], or as a compound to enhance hardness, brittleness, and the glass transition temperature (T g ) of prepared polymers and composites [ 35 , 36 ]. Furthermore, isosorbide dimethacrylate exhibits relatively low apparent viscosity values (tens to hundreds of mPa · s) which can be useful applications that require decreased viscosity while the retaining the final material properties [37]. This article shall be focused on the study of the synthesis of isosorbide from sorbitol using a commercially available acid (p-toluenesulfonic acid) as a catalyst via dehydration (intramolecular nucleophilic substitution). The appropriate conditions, such as the optimal reaction temperature or the effective amount of catalyst, will be investigated in order to accomplish the highest possible yield of formed isosorbide. Afterward, the synthesis of isosorbide dimethacrylate will be performed using methacrylic anhydride as a nucleophile involving the presence of an environmentally friendly catalyst—potassium acetate—which is an alternative to widely used DMAP as a catalyst. Numerous analytical methods (such as electrospray mass spectrometry (MS), nuclear magnetic resonance (NMR), and X-ray diffraction (XRD)) will be used for the structural verification of all synthesized products. The formed polymerizable diester of isosorbide will be characterized via differential scanning calorimetry (DSC) to prove the reactivity of the compound and its ability to be polymerized. In addition, thermal gravimetric analysis (TGA) will be performed to describe the heat-resistant index of the synthesized isosorbide dimethacrylate. Eventually, isosorbide dimethacrylate will be used to enhance the dynamic mechanical properties of previously synthesized polymerizable monoesters of 2-hydroxypropanoic acid and 3-hydroxybutanoic acid to describe the effect on the characteristics of the final resin. 2. Materials and Methods 2.1. Materials Sorbitol (D-glucitol, 98%) used for the synthesis of isosorbide was purchased from Fichema s.r.o. (Brno, Czech Republic). The catalyst for the dehydration (para-toluenesulfonic acid (p-TSA), monohydrate, 98%, for synthesis) was acquired from Sigma-Aldrich (St. Louis, MO, USA). Methacrylic anhydride (94%, for synthesis) used for the modification of isosorbide to isosorbide dimethacrylate was obtained from Sigma-Aldrich (St. Louis, MO, USA). Other chemicals used in the described syntheses, namely potassium acetate (p.a.) as catalyst and sodium hydroxide (p.a.) as neutralizing agent, were obtained from PENTA s.r.o. (Prague, Czech Republic). Initiators for the curing experiments such as Luperox ® DI, tert-Butyl peroxide (for synthesis), or phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide (BAPO, 97%) were purchased from Sigma-Aldrich (St. Louis, MO, USA). 2.2. Analytical Methods for Structural Characterization 2.2.1. Fourier-Transform Infrared Spectroscopy (FT-IR) Fourier-transform infrared spectroscopy served as a structural verification method. In the case of a particular synthesis of isosorbide dimethacrylate, it proved the disappearance of hydroxyl groups and the presence of ester bonding. Spectra were recorded by the infrared spectroscope Bruker Tensor 27 (Billerica, MA, USA) with attenuated total reflectance (ATR) (the dispersion component was a diamond). The irradiation source was an LED laser. The application of Michelson interferometer was required since Fourier transformation Polymers 2023,15, 3640 3 of 18 was performed. In total, 32 scans were obtained in 1 measurement with a measurement resolution of 2 cm−1. 2.2.2. Mass Spectrometry (MS) The spectrometer used for MS was a Bruker EVOQ LC-TQ (Billerica, MA, USA). Set MS conditions: ESI in positive; spray voltage 3500 V; cone temperature tempered at 340 ◦ C; cone gas flow 30 a.u.; heated probe temperature 640 ◦ C; probe gas flow 45 a.u., nebulizer gas flow 60 a.u.; and exhaust gas on. MRM transition for isosorbide (ISD): RT 0.78 min; 147.1 > 87.3 CE with 7.5 eV. Argon was used as a collision gas at a pressure of 1.4 mTorr. In addition, isosorbide dimethacrylate (ISDMMA) was verified by product scan; therefore, the mass spectrum of this compound was gained. Agilent Ion Trap 6320 LC/MS (Santa Clara, CA, USA) was set to the following working setup: nebulizer 172 kPa; drying gas flow 10 L/min; temperature of drying gas 350 ◦ C; ionization mode ESI +; and complete scan used at a scan interval of 130–810 m/z. 2.2.3. X-ray Diffraction Analysis (XRD) XRD analyses were performed via X-ray instrumentation EMPYREAN (PANalytical, Malvern, UK) in a working setup with Bragg–Brentano parafocusing composition withCuK α radiation. The set conditions were: range 4–85 ◦ second, step resolution 0.015 ◦ second; voltage 40 kV; current applied 30 mA; ADS 10 mm; time per step 93 s; no monochromator. 2.2.4. Nuclear Magnetic Resonance (NMR) Nuclear magnetic resonance (NMR) was performed for the detailed structural verification of produced compounds. The measurements were obtained by a Bruker Avance III 500 MHz (Bruker Billerica, MA, USA) at the temperature of 30 ◦ C using deuterium chloroform (CDCl 3 ) as a dispersion continuum along with tetramethylsilane as an internal standardized compound (TMS) for these purposes. The acquisition time was 4.0 s. The chemical shift ( δ ) units are part per million (ppm) with reference to TMS. Coupling constants J(with a unit of (Hz)) were described as follows: s for the singlet, d for the doublet, t for the triplet, q for the quartet, p for the quintet, m for the multiplet. 2.3. Synthesis of Isosorbide form Sorbitol Sorbitol (400 g, 2.2 mol) was added into a 1 L jacket reactor homogenized with a stirrer (500 rpm) and the reactor was heated up to the reaction temperature ( 120–140 ◦C ). A vacuum pump was applied to the apparatus and the pressure was decreased to approximately 1–2 kPa to separate adsorbed water from sorbitol. The particular amount of catalyst (p-TSA, 0.25–1.00 mol.%) was added after 15 min of homogenization and the pressure decrease was set to 3.5–5 kPa. Reaction water was continuously distilled and condensed during the reaction. When the reaction time expired (5 h), the catalyst was neutralized with sodium hydroxide and then the product (isosorbide) was distilled from the batch. The conditions of the separation were 0.3–0.5 kPa and 180–200 ◦ C. Distilled and condensed isosorbide was left to spontaneously crystallize and it was structurally characterized afterwards. Reaction schemes, including the dehydration of sorbitol to isosorbide (including sorbitan as an intermediate), are displayed in Schemes 1and 2. 2.4. Synthesis of Isosorbide Dimethacrylate Previously synthesized and characterized isosorbide (200 g, 1.4 mol) was poured into a round-bottomed flask that was transferred into an oil bath for temperature regulation. The temperature was set at 70 ◦ C and a magnetic stirrer was applied. Once isosorbide reached the required temperature, methacrylic anhydride (432 g, 2.8 mol) was added into the flask and the temperature of the mixture was increased to 70 ◦ C again. Then, the catalyst was added to the mixture (potassium acetate, 6.9 g, 0.014 mol) and the reaction was performed for 8 h and monitored via GC-FID analysis. The reaction mixture was purified of the formed methacrylic acid by neutralization by sodium hydroxide and formed methacrylate salts Polymers 2023,15, 3640 4 of 18 were extracted by distilled water. Eventually, neutralized isosorbide dimethacrylate was dried with sodium sulfate, filtered, and structurally characterized. The reaction mechanism is displayed in Scheme 3. Polymers 2023, 15, x FOR PEER REVIEW 4 of 18 Scheme 1. The reaction mechanism of the dehydration of D-glucitol to 1,4-anhydro-D-glucitol in the presence of catalyst p-TSA (para-toluenesulfonic acid). Scheme 2. The reaction mechanism of the dehydration of 1,4-anhydro-D-glucitol to 1,4:3,6-dianhydro-D-glucitol in the presence of catalyst p-TSA (para-toluenesulfonic acid). 2.4. Synthesis of Isosorbide Dimethacrylate Previously synthesized and characterized isosorbide (200 g, 1.4 mol) was poured into a round-bottomed flask that was transferred into an oil bath for temperature regulation. The temperature was set at 70 °C and a magnetic stirrer was applied. Once isosorbide reached the required temperature, methacrylic anhydride (432 g, 2.8 mol) was added into the flask and the temperature of the mixture was increased to 70 °C again. Then, the catalyst was added to the mixture (potassium acetate, 6.9 g, 0.014 mol) and the reaction was performed for 8 h and monitored via GC-FID analysis. The reaction mixture was purified of the formed methacrylic acid by neutralization by sodium hydroxide and formed methacrylate salts were extracted by distilled water. Eventually, neutralized isoScheme 1. The reaction mechanism of the dehydration of D-glucitol to 1,4-anhydro-D-glucitol in the presence of catalyst p-TSA (para-toluenesulfonic acid). Polymers 2023, 15, x FOR PEER REVIEW 4 of 18 Scheme 1. The reaction mechanism of the dehydration of D-glucitol to 1,4-anhydro-D-glucitol in the presence of catalyst p-TSA (para-toluenesulfonic acid). Scheme 2. The reaction mechanism of the dehydration of 1,4-anhydro-D-glucitol to 1,4:3,6-dianhydro-D-glucitol in the presence of catalyst p-TSA (para-toluenesulfonic acid). 2.4. Synthesis of Isosorbide Dimethacrylate Previously synthesized and characterized isosorbide (200 g, 1.4 mol) was poured into a round-bottomed flask that was transferred into an oil bath for temperature regulation. The temperature was set at 70 °C and a magnetic stirrer was applied. Once isosorbide reached the required temperature, methacrylic anhydride (432 g, 2.8 mol) was added into the flask and the temperature of the mixture was increased to 70 °C again. Then, the catalyst was added to the mixture (potassium acetate, 6.9 g, 0.014 mol) and the reaction was performed for 8 h and monitored via GC-FID analysis. The reaction mixture was purified of the formed methacrylic acid by neutralization by sodium hydroxide and formed methacrylate salts were extracted by distilled water. Eventually, neutralized isoScheme 2. The reaction mechanism of the dehydration of 1,4-anhydro-D-glucitol to 1,4:3,6-dianhydroD-glucitol in the presence of catalyst p-TSA (para-toluenesulfonic acid). Polymers 2023,15, 3640 5 of 18 Polymers 2023, 15, x FOR PEER REVIEW 5 of 18 sorbide dimethacrylate was dried with sodium sulfate, filtered, and structurally characterized. The reaction mechanism is displayed in Scheme 3. Scheme 3. The mechanism of the nucleophilic substitution reaction leading to the formation of isosorbide dimethacrylate using methacrylic anhydride as the reactant. 2.5. Analytical Methods for Kinetics Study of Syntheses 2.5.1. Liquid Chromatography with Mass Spectrometry (LC-MS) Samples of isosorbide gained during a continuous reaction were analyzed by UHPLC Agilent 1290 Infinity LC (Santa Clara, CA, USA) connected with triple quadrupole (Bruker EVOQ LC-TQ) (Billerica, MA, USA) equipped with atmospheric ESI. An external source of nitrogen and air (generator of gases: Peak Scientific—Genius 3045) (Glasgow, Scotland) was used. Luna® Omega Polar C18 Phenomenex (100 × 2.1 mm, 1.6 µm) (Torrance, CA, USA) was the stationary phase. The working column temperature was set to 40 °C while the flow rate reached 0.5 mL/min. Mobile phases responsible for the separation in LC were (A) 0.1% HCOOH in MilliQ water and (B) acetonitrile, and used in the following conditions: An eluent (%): t(0 min) = 85, t(0.6 min) = 80, t(3.7 min) = 5, t(4.8 min) = 90. Analyses were stopped after 6.0 min, and re-equilibration took 2.0 min. The injection volume was 7 µL. Mass spectrometry parameters were described earlier (see Section 2.2.2). 2.5.2. Gas Chromatography with Flame Ionization Detector (GC-FID) Samples were obtained during the methacrylation of isosorbide, and quantification of reactants (methacrylic anhydride and methacrylic acid) was performedvia GC-FID Hewlett Packard 5890 Series II (Palo Alto, CA, USA). Nitrogen (as an auxiliary gas), air (as an oxidizer), and hydrogen (as a carrier) were applied to the instrumentation for measurements. The stationary phase was ZB-624 (60 m × 0.32 mm, 1.8 µm). Inlet temperature: 210 °C; detector temperature: 250 °C. The temperature gradient was applied, the initial temperature was 60 °C (1-minute maintenance) then at emperature rate of 20 °C/min was used and the eventual temperature was 260 °C (tempered for 15 min). The flow of the analyzed mixture was 3 mL/min with a 1:40 split ratio. Injection volume: 1 µL. Retention times of measured compounds: methacrylic anhydride (MAA) (RT9.88 min); methacrylic acid (MA) (RT 6.05 min). Scheme 3. The mechanism of the nucleophilic substitution reaction leading to the formation of isosorbide dimethacrylate using methacrylic anhydride as the reactant. 2.5. Analytical Methods for Kinetics Study of Syntheses 2.5.1. Liquid Chromatography with Mass Spectrometry (LC-MS) Samples of isosorbide gained during a continuous reaction were analyzed by UHPLC Agilent 1290 Infinity LC (Santa Clara, CA, USA) connected with triple quadrupole (Bruker EVOQ LC-TQ) (Billerica, MA, USA) equipped with atmospheric ESI. An external source of nitrogen and air (generator of gases: Peak Scientific—Genius 3045) (Glasgow, Scotland) was used. Luna ® Omega Polar C18 Phenomenex (100 × 2.1 mm, 1.6 µ m) (Torrance, CA, USA) was the stationary phase. The working column temperature was set to 40 ◦ C while the flow rate reached 0.5 mL/min. Mobile phases responsible for the separation in LC were (A) 0.1% HCOOH in MilliQ water and (B) acetonitrile, and used in the following conditions: An eluent (%): t(0 min) = 85, t(0.6 min) = 80, t(3.7 min) = 5, t(4.8 min) = 90. Analyses were stopped after 6.0 min, and re-equilibration took 2.0 min. The injection volume was 7 µ L. Mass spectrometry parameters were described earlier (see Section 2.2.2). 2.5.2. Gas Chromatography with Flame Ionization Detector (GC-FID) Samples were obtained during the methacrylation of isosorbide, and quantification of reactants (methacrylic anhydride and methacrylic acid) was performedvia GC-FID Hewlett Packard 5890 Series II (Palo Alto, CA, USA). Nitrogen (as an auxiliary gas), air (as an oxidizer), and hydrogen (as a carrier) were applied to the instrumentation for measurements. The stationary phase was ZB-624 (60 m × 0.32 mm, 1.8 µ m). Inlet temperature: 210 ◦ C; detector temperature: 250 ◦ C. The temperature gradient was applied, the initial temperature was 60 ◦ C (1-min maintenance) then at emperature rate of 20 ◦ C/min was used and the eventual temperature was 260 ◦ C (tempered for 15 min). The flow of the analyzed mixture was 3 mL/min with a 1:40 split ratio. Injection volume: 1 µ L. Retention times of measured compounds: methacrylic anhydride (MAA) (RT9.88 min); methacrylic acid (MA) (RT 6.05 min). Polymers 2023,15, 3640 6 of 18 2.6. Reactivity and Thermal Stability Characterization of Isosorbide Dimethacrylate 2.6.1. Differential Scanning Calorimetry (DSC) DSC was used to describe the reactivity kinetics of produced polymerizable isosorbide dimethacrylate. The product was mixed with a thermo-initiator, namely Luperox ® DI (1% w/wamount). Aluminum pans (10–15 mg) were filled with the mixtures and were hermetically sealed. Instrument DSC 2500 model (TA Instruments) (New Castle, DE, USA) was the instrumentation used for measurements. Four different heating rates were performed on each sample from temperatures of 10 to 245 ◦ C while the continual temperature increases were: 5; 10; 15 and 20 ◦ C/min. One measurement cycle was performed for each sample since the initiator reacted during one cycle. An inert atmosphere (nitrogen) was applied during all measurements. 2.6.2. Thermogravimetric Analysis (TGA) TGA was used to acquire the heat stability index of polymerized isosorbide dimethacrylate. Used samples were obtained similarly to the samples for FT-IR curability analysis. ISDMMA was mixed with BAPO (1% w/w), polymerized by the photoinitiator for 30 min using an LED irradiation source of 405 nm wavelength. The instrumentation used was a TGA Q500 from (TA Instruments) (New Castle, DE, USA). Analyzed samples (around 15 mg) were measured in the following conditions: equilibration at 35 ◦ C; temperature increase to 600 ◦ C with applied temperature ramp of 10 ◦ C/min under nitrogen; 15 min at 600 ◦C under an oxidizing environment. 2.7. Thermo-Mechanical Characterization of Synthesized Isosorbide Dimethacrylate Containing Resins Dynamic Mechanical Analysis (DMA) The thermo-mechanical properties of mixtures containing isosorbide dimethacrylate with resin precursors based on methacrylated 3-hydroxybutyrates (see Figure 1) were measured with DMA 2980 from (TA Instruments, New Castle, DE, USA). The measured objects were prepared from isosorbide dimethacrylate and methacrylated alkyl 3-hydroxybutyrate with a specified amount of ISDMMA in the mixture (0–10% w/w of ISDMMA). Then, 1% w/w of BAPO was added and precursors were polymerized for 30 min (405 nm LED). Tested objects had parameters: 60 × 10 × 2 mm. Objects were applied into a dual cantilever attachment and the parameters of applied deformation were: 10 µ m amplitude, 1 Hz frequency. The temperature increase was from 25 ◦ C to 120 ◦ C with an increase rate of 3◦C/min temperature. 3. Results and Discussion 3.1. Isosorbide Synthesis and Characterization The monitoring of isosorbide synthesis was realized via the weighing of the condensed reaction water as a very quick a simple method to determine the most appropriate reaction temperature. The results of the collected reaction water formed during the dehydration are shown in Figure 1a. Once the most optimal temperature was determined, the reaction kinetics monitoring next focused on the differing amount of the catalyst in the reaction mixture. These reactions were monitored more precisely using LC-MS as a quantification method for isosorbide as a forming product. This study was performed to obtain information regarding the differences in the rate of reaction based on the quantity of the catalyst. The results of these measurements are displayed in Figure 1b. Polymers 2023,15, 3640 7 of 18 Polymers 2023, 15, x FOR PEER REVIEW 7 of 18 (a) (b) Figure 1. (a) The dependence of formed and condensed reaction water during the dehydration reaction resulting in the production of isosorbide on the reaction time at different temperatures; (b) Monitoring of the synthesis of isosorbide via LC–MS analysis for differing amounts of catalyst (p-TSA) at 130 °C. The results showed that the most appropriate reaction temperature was 130 °C as the equilibrium at this temperature was reached while almost the exact theoretical amount of condensed reaction water (101.5%) was collected. At the temperature of 140 °C, more than the theoretical quantity of water was collected, which indicated the occurrence of side reactions forming degradation products. The degradation products that cannot be further dehydrated forming isosorbide are 1,5-sorbitan and 2,5-sorbitan [11,13]. These compounds are also formed and the reaction water is generated during this process. However, a temperature of 120 °C exhibited a much lower reaction rate than 130 °C. From these results, the dependence of isosorbide analyzed yield (via LC-MS) on time was described at the reaction temperature of 130 °C. LC-MS analysis revealed that 1% w/w of the used catalyst (p-TSA) led to the highest yield of formed isosorbide (81.9%). Lower amounts of catalyst led to significantly lower yields compared to 1% w/w catalyst. In particular, 0.5% w/w catalyst resulted in a yield value of 56.4% and 0.25% w/w catalyst reached 41.5% of isosorbide yield. Structural verification via the FT-IR method is shown in Figure 2. The spectrum is a characteristic fingerprint of the compound. The signal at approximately 3600–3100 cm−1 is extremely intense as the isosorbide molecule contains two hydroxyl groups that are significant for the further modification to isosorbide dimethacrylate. This method was also used to confirm the presence of modifiable hydroxyl groups in the structure. This IR spectrum of isosorbide can be compared to published spectra in literature [38]. Figure 1. ( a ) The dependence of formed and condensed reaction water during the dehydration reaction resulting in the production of isosorbide on the reaction time at different temperatures; ( b ) Monitoring of the synthesis of isosorbide via LC–MS analysis for differing amounts of catalyst (p-TSA) at 130 ◦C. The results showed that the most appropriate reaction temperature was 130 ◦ C as the equilibrium at this temperature was reached while almost the exact theoretical amount of condensed reaction water (101.5%) was collected. At the temperature of 140 ◦ C, more than the theoretical quantity of water was collected, which indicated the occurrence of side reactions forming degradation products. The degradation products that cannot be further dehydrated forming isosorbide are 1,5-sorbitan and 2,5-sorbitan [ 11 , 13 ]. These compounds are also formed and the reaction water is generated during this process. However, a temperature of 120 ◦ C exhibited a much lower reaction rate than 130 ◦ C. From these results, the dependence of isosorbide analyzed yield (via LC-MS) on time was described at the reaction temperature of 130 ◦ C. LC-MS analysis revealed that 1% w/wof the used catalyst (p-TSA) led to the highest yield of formed isosorbide (81.9%). Lower amounts of catalyst led to significantly lower yields compared to 1% w/wcatalyst. In particular, 0.5% w/wcatalyst resulted in a yield value of 56.4% and 0.25% w/wcatalyst reached 41.5% of isosorbide yield. Structural verification via the FT-IR method is shown in Figure 2. The spectrum is a characteristic fingerprint of the compound. The signal at approximately 3600–3100 cm −1 is extremely intense as the isosorbide molecule contains two hydroxyl groups that are significant for the further modification to isosorbide dimethacrylate. This method was also used to confirm the presence of modifiable hydroxyl groups in the structure. This IR spectrum of isosorbide can be compared to published spectra in literature [38]. Polymers 2023, 15, x FOR PEER REVIEW 8 of 18 Figure 2. FT-IR spectrum of synthesized isosorbide. Mass spectrometry confirmed the structure of isosorbide and the spectrum is shown in Figure 3. The fragmentation of isosorbide corresponds with the prediction; the molecular ion peak obtained via mass spectrometry and present in the spectrum has the exact value of m/z (147.2 m/z). Figure 3. MS fragmentation spectrum of synthesized isosorbide. X-ray diffraction analysis also verified the structure of the synthesized product. This method was used since isosorbide has a crystalline form. The XRD spectrum with the particular values of 2θ is presented in Figure 4. This spectrum also serves as a fingerprint of the molecule. Furthermore, the XRD spectrum of isosorbide was already published and is comparable with that obtained in this article [39]. Figure 2. FT-IR spectrum of synthesized isosorbide. Polymers 2023,15, 3640 8 of 18 Mass spectrometry confirmed the structure of isosorbide and the spectrum is shown in Figure 3. The fragmentation of isosorbide corresponds with the prediction; the molecular ion peak obtained via mass spectrometry and present in the spectrum has the exact value of m/z(147.2 m/z). Polymers 2023, 15, x FOR PEER REVIEW 8 of 18 Figure 2. FT-IR spectrum of synthesized isosorbide. Mass spectrometry confirmed the structure of isosorbide and the spectrum is shown in Figure 3. The fragmentation of isosorbide corresponds with the prediction; the molecular ion peak obtained via mass spectrometry and present in the spectrum has the exact value of m/z (147.2 m/z). Figure 3. MS fragmentation spectrum of synthesized isosorbide. X-ray diffraction analysis also verified the structure of the synthesized product. This method was used since isosorbide has a crystalline form. The XRD spectrum with the particular values of 2θ is presented in Figure 4. This spectrum also serves as a fingerprint of the molecule. Furthermore, the XRD spectrum of isosorbide was already published and is comparable with that obtained in this article [39]. Figure 3. MS fragmentation spectrum of synthesized isosorbide. X-ray diffraction analysis also verified the structure of the synthesized product. This method was used since isosorbide has a crystalline form. The XRD spectrum with the particular values of 2 θ is presented in Figure 4. This spectrum also serves as a fingerprint of the molecule. Furthermore, the XRD spectrum of isosorbide was already published and is comparable with that obtained in this article [39]. Polymers 2023, 15, x FOR PEER REVIEW 9 of 18 Figure 4. XRD spectrum of synthesized isosorbide. Structural verification was also provided via the 1 H NMR method and the final spectrum is shown in Figure 5. All peaks with appropriate chemical shifts have the same positions as the prediction. Shifts and coupling constants are described in Figure 5. Figure 5. 1 H NMR spectrum of isosorbide (d-chloroform, 500 MHz): δ (ppm) = 4.69 (dd,1H), 4.37 (m, 2H), 4.29 (q, 1H), 3.87 (m, 3H), 3.52 (dd, 1H), 2.67 (s, 1H), 1.69 (s, 1H). 3.2. Isosorbide Dimethacrylate Synthesis and Characterization The synthesis of isosorbide dimethacrylate involved a reaction with methacrylic anhydride (MAA) (catalysis of potassium acetate) and the products of this particular nucleophilic substitution are the ester of isosorbide and the secondary product—methacrylic acid (MA) (see Scheme 3). The principle chosen for reaction kinetics monitoring was to quantify the decreasing reactant (MAA) and at the same time quantify the formation of methacrylic acid (MA). Since these two substances can be vaporized, GC-FID was used for the quantification. The reaction mixture consisted of an equimolar amount of MAA to isosorbide; therefore, equilibrium heading to the minimization of MAA in the mixture was awaited. The results of GC-FID quantification of the mentioned compounds are displayed in Figure 6. Figure 4. XRD spectrum of synthesized isosorbide. Structural verification was also provided via the 1 H NMR method and the final spectrum is shown in Figure 5. All peaks with appropriate chemical shifts have the same positions as the prediction. Shifts and coupling constants are described in Figure 5. 3.2. Isosorbide Dimethacrylate Synthesis and Characterization The synthesis of isosorbide dimethacrylate involved a reaction with methacrylic anhydride (MAA) (catalysis of potassium acetate) and the products of this particular nucleophilic substitution are the ester of isosorbide and the secondary product—methacrylic acid (MA) (see Scheme 3). The principle chosen for reaction kinetics monitoring was to quantify the decreasing reactant (MAA) and at the same time quantify the formation of methacrylic acid (MA). Since these two substances can be vaporized, GC-FID was used for the quantification. The reaction mixture consisted of an equimolar amount of MAA to isosorbide; therefore, equilibrium heading to the minimization of MAA in the mixture was awaited. The results of GC-FID quantification of the mentioned compounds are displayed in Figure 6. Polymers 2023,15, 3640 9 of 18 Polymers 2023, 15, x FOR PEER REVIEW 9 of 18 Figure 4. XRD spectrum of synthesized isosorbide. Structural verification was also provided via the 1 H NMR method and the final spectrum is shown in Figure 5. All peaks with appropriate chemical shifts have the same positions as the prediction. Shifts and coupling constants are described in Figure 5. Figure 5. 1 H NMR spectrum of isosorbide (d-chloroform, 500 MHz): δ (ppm) = 4.69 (dd,1H), 4.37 (m, 2H), 4.29 (q, 1H), 3.87 (m, 3H), 3.52 (dd, 1H), 2.67 (s, 1H), 1.69 (s, 1H). 3.2. Isosorbide Dimethacrylate Synthesis and Characterization The synthesis of isosorbide dimethacrylate involved a reaction with methacrylic anhydride (MAA) (catalysis of potassium acetate) and the products of this particular nucleophilic substitution are the ester of isosorbide and the secondary product—methacrylic acid (MA) (see Scheme 3). The principle chosen for reaction kinetics monitoring was to quantify the decreasing reactant (MAA) and at the same time quantify the formation of methacrylic acid (MA). Since these two substances can be vaporized, GC-FID was used for the quantification. The reaction mixture consisted of an equimolar amount of MAA to isosorbide; therefore, equilibrium heading to the minimization of MAA in the mixture was awaited. The results of GC-FID quantification of the mentioned compounds are displayed in Figure 6. Figure 5. 1 H NMR spectrum of isosorbide (d-chloroform, 500 MHz): δ (ppm) = 4.69 (dd,1H), 4.37 (m, 2H), 4.29 (q, 1H), 3.87 (m, 3H), 3.52 (dd, 1H), 2.67 (s, 1H), 1.69 (s, 1H). Polymers 2023, 15, x FOR PEER REVIEW 10 of 18 Figure 6. GC-FID analyzed the quantification of decreasing methacrylic anhydride (MAA) and increasing methacrylic acid (MA). It is evident that the majority of methacrylic anhydride reacted (94.1%) and that equilibrium tended to occur after 8 h of reaction. Simultaneously, the conversion of the forming methacrylic acid (95.1%) corresponded with the decrease in MAA. After purification and drying, isosorbide dimethacrylate was harvested resulting, in an ISDMMA yield of 71% of the theory. This decrease in product yield compared to the theoretical yield can be caused by the minor formation of isosorbide monomethacrylate, which is water-soluble and could be extracted from the mixture during the purification process. The FT-IR spectrum of synthesized isosorbide dimethacrylate is displayed in Figure 7. The hydroxyl region (3600–3100 cm−1) completely disappeared, which confirmed the modification via esterification. The presence of ester bonding is proved by signals at wavenumber intervals of 1750–1735 cm−1 (referring to C=O stretching) and 1210–1150 cm−1 (belonging to C-O stretching). Since methacrylic functional groups contain unsaturated double bonds, those could be verified via signals at 1670–1600 cm−1 (C=C stretching) and 970–930 cm−1 and 850–800 cm−1 (C=C bending). Figure 7. FT-IR spectrum of synthesized isosorbide dimethacrylate. Figure 6. GC-FID analyzed the quantification of decreasing methacrylic anhydride (MAA) and increasing methacrylic acid (MA). It is evident that the majority of methacrylic anhydride reacted (94.1%) and that equilibrium tended to occur after 8 h of reaction. Simultaneously, the conversion of the forming methacrylic acid (95.1%) corresponded with the decrease in MAA. After purification and drying, isosorbide dimethacrylate was harvested resulting, in an ISDMMA yield of 71% of the theory. This decrease in product yield compared to the theoretical yield can be caused by the minor formation of isosorbide monomethacrylate, which is water-soluble and could be extracted from the mixture during the purification process. The FT-IR spectrum of synthesized isosorbide dimethacrylate is displayed in Figure 7 . The hydroxyl region (3600–3100 cm −1 ) completely disappeared, which confirmed the modification via esterification. The presence of ester bonding is proved by signals at wavenumber Polymers 2023,15, 3640 16 of 18 Institutional Review Board Statement: Not applicable. Informed Consent Statement: Not applicable. Data Availability Statement: Not applicable. Conflicts of Interest: The authors declare no conflict of interest. References 1. Ternel, J.; Lopes, A.; Sauthier, M.; Buffe, C.; Wiatz, V.; Bricout, H.; Tilloy, S.; Monflier, E. 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