In the present work, a new series of cross-linked copolymers based on itaconic anhydride and methyl methacrylate were prepared employing free radical copolymerization in the presence of azobisisobutyronitrile as an initiator and 2-butanone as a solvent under microwave irradiation. The copolymers containing itaconic anhydride (ITA) and methyl methacrylate (MMA) were chosen due to the formation of long-term stable anhydride moieties, which might be useful to attach enzymes covalently with numerous applications in water treatment. The copolymerization process was carried out in the presence of two types of cross-linking agent, namely, ethylene dimethacrylate (EDMA) and divinylbenzene (DVB) in a range of 0-20% (
Microwave irradiation has become a common heat source in organic chemistry [
The synthesis of cross-linked polymers is one way to improve the thermal and mechanical properties of polymers; the cross-linking density in the polymer network and the molecular weight of the polymers between the crosslinking points have an effect on the properties of cross-linked polymers [
Cross-linked polymers can be prepared via chemical (covalent or ionic bonds) or physical (hydrogen bonds, Van der Waals, or other interactions) cross-linking [
Itaconic anhydride (ITA) can be obtained from renewable resources such as plants produced from the fermentation of carbohydrates, which forms itaconic acid that can be converted into anhydride via dehydration or by the pyrolysis of citric acid [
In addition, ITA has extensively been used in industrial applications as comonomer, for instance, as an essential for rubber materials, paints and colors, coatings, biodegradable polymers, contact lenses, or medicinal applications [
In addition, methyl methacrylate (MMA) comonomer provides mechanical stability for the copolymer and chemical resistance against a number of organic solvents. Furthermore, it has advantages of poly(methyl methacrylate) (PMA), which is considered to have good adhesion to different surfaces and the transparency coating [
Accordingly, the present work represents the synthesis of a new series of cross-linked copolymers based on different ratios of ITA and MMA using a microwave irradiation. Samples of copolymers were prepared using various types of cross-linking agents and different degrees of crosslinking to explore their effect on the thermal properties and the morphology of the as-obtained cross-linked polymers. Two types of cross-linking agents, ethylene dimethacrylate (EDMA) and divinylbenzene (DVB), were used with the degree of cross-linking in the range of 0-20% (
Methyl methacrylate (MMA), itaconic anhydride (ITA), ethylene dimethacrylate (EDMA), divinylbenzene (DVB), and
A microwave (Monowave 300, Aton Paar GmbH, 1400 W maximum magnetron, Germany) with a maximum filling volume of 6 and 20 mL for 10 and 30 mL vials, respectively. Maximum operating pressure of 30 bar, maximum IR temperature of 300°C, maximum fibre-optic temperature of 300°C, and maximum power of 850 W were used. The vials were constructed from borosilicate glass and silicon carbide using PEEK caps and Teflon-coated silicone seals.
The functional groups of the prepared cross-linked copolymers were investigated by Fourier-transform infrared (FT-IR) spectroscopy. The thermal properties were studied using thermogravimetric analysis (Q500 TGA, USA) under nitrogen atmosphere within the temperature range 30 to 800°C and at the heating rate 10°C/min. The morphology of the prepared copolymers was studied using scanning electron microscopy (SEM). The specific surface area and the pore size distribution were investigated by applying Brunauer-Emmett-Teller (BET) theory and Barrett-Joyner-Halenda (BJH) model using Micromeritics (ASAP-2020, USA) at the temperature 77 K.
Cross-linked copolymers were prepared using microwave-assisted method (Monowave 300, Anton Paar) as described elsewhere [
Summary of the copolymer’s ratio and yield.
Copolymer code | Cross-linking agent (%/g) | MMA/ITA ratio | MMA (g/mmol) | ITA (g/mmol) | AIBN |
Yield (g) | |
---|---|---|---|---|---|---|---|
EPMITA 1-5 | EDMA | 5/0.1621 | 1 : 2 | 1.0012/10 | 2.2416/20 | 0.1702 | 0.85 |
EPMITA 1-10 | 10/0.3243 | 0.1784 | 2.56 | ||||
EPMITA 1-15 | 15/0.4864 | 0.1864 | 2.15 | ||||
EPMITA 1-20 | 20/0.6486 | 0.1945 | 1.80 | ||||
EPMITA 2-15 | 15/0.3183 | 1 : 1 | 1.0012/10 | 1.1208/10 | 0.1220 | 1.70 | |
EPMITA 2-20 | 20/0.4244 | 0.1273 | 1.90 | ||||
EPMITA 3-15 | 15/0.4685 | 2 : 1 | 2.0024/20 | 1.1208/10 | 0.1795 | 2.10 | |
EPMITA 3-20 | 20/0.6246 | 0.1874 | 2.84 | ||||
DPMITA 1-5 | DVB | 5/0.1621 | 1 : 2 | 1.0012/10 | 2.2416/20 | 0.1702 | 1.20 |
DPMITA 1-10 | 10/0.3243 | 0.1784 | 2.80 | ||||
DPMITA 1-15 | 15/0.4864 | 0.1864 | 1.80 | ||||
DPMITA 1-20 | 20/0.6486 | 0.1945 | 2.52 | ||||
DPMITA 2-5 | 5/0.1061 | 1 : 1 | 1.0012/10 | 1.1208/10 | 0.1114 | 1.60 | |
DPMITA 2-10 | 10/0.2122 | 0.1167 | 1.80 | ||||
DPMITA 3-5 | 5/0.1562 | 2 : 1 | 2.0024/20 | 1.1208/10 | 0.1717 | 2.20 | |
DPMITA 3-10 | 10/0.3123 | 0.1717 | 2.40 |
The precipitated final products, DPMITA 1-5, EPMITA 1-5, EPMITA 1-10, EPMITA 1-15, and EPMITA 1-20, were washed with diethyl ether and dried in a vacuum oven at 40°C for 24 h.
The other final products, DPMITA 1-10, DPMITA 1-15, and DPMITA 1-20, were washed with acetone, and dried in a vacuum oven at 40°C for 24 h.
Various copolymer compositions can produce a very large number of different arrangements, producing materials of varying chemical and physical properties. Thus, the hydrophilicity of copolymers can be modified by changing the amount of incorporated itaconic anhydride [
Different ratios of itaconic anhydride (ITA) and methyl methacrylate (MMA) were mixed in 2-butanone as solvent in the presence of AIBN (5%) as an initiator for 5 min at 120°C using a microwave-assisted free radical copolymerization (Scheme
Copolymerization of itaconic anhydride and methyl methacrylate in the presence of ethylene dimethacrylate (EDMA) and divinylbenzene (DVB) as cross-linking agents.
It was noticed that the polymer preferred to form a precipitate rather gel during the copolymerization process upon increasing the ratio of the cross-linking agent at a monomer ratio of
Photograph of the (a) EPMITA 1-20, (b) EPMITA 1-15, (c) EPMITA 1-10, (d) EPMITA 1-5, (e) DPMITA 2-5, and (f) DPMITA 2-10 copolymers.
Photograph of the (a) EPMITA 2-20, (b) EPMITA 3-20, (c) DPMITA 3-5, and (d) DPMITA 2-5 copolymers.
The FTIR spectra of the different compositions of ITA and MMA (EPMITA and DPMITA) in the presence of different cross-linking agents ethylene dimethacrylate and divinylbenzene were studied. The copolymer ITA-MMA (EPMTITA) using ethylene dimethacrylate showed characteristic bands at 1863 and 1783 cm-1 for ITA (C=O) (symmetric and asymmetric stretching of the carbonyl in the 5-membered anhydride ring) and 1724-1728 cm-1 for the stretching carbonyl group of the ester corresponding to MMA residue, beside a characteristic band at 1640 cm-1 related to the stretching C=O ester of the cross-linking agent (EDMA) (Figures
FT-IR of EPMITA and DPMITA copolymers: (a) EPMITA 1-5, EPMITA 1-10, and EPMITA 1-15; (b) EPMITA 1-15 and EPMITA 3-15; (c) EPMITA 1-20 and EPMITA 3-20; (d) DPMITA 1-10, DPMITA 2-10, and DPMITA 3-10; (e) DPMITA 1-15, DPMITA 2-15, and DPMITA 3-15.
FT-IR peaks observed for the EPMITA and DPMITA copolymers.
Functional group | Peak assignment | Wavenumber (cm-1) | |
---|---|---|---|
EPMITA copolymers | DPMITA copolymers | ||
Aliphatic | C–H stretching of methyl | 2955-2958 | 2954-2957 |
Aliphatic backbone stretching | 1437-1451 | 1438-1449 | |
Carbonyl group | C=O stretching (anhydride) (C=O symmetric and asymmetric) | 1783-1863 | 1780-1782 |
C=O stretching methyl methacrylate | 1724-1728 | 1709-1728 | |
C=O stretching (ester) EDMA | 1636-1640 | — | |
Ether | Stretching vibration of C-O-C | 1160-1242 | 1155-1232 |
Aromatic | Aromatic C-H stretch | — | 2995-3004 |
Aromatic =CH stretch | — | 1631-1640 | |
Aromatic =CH bending | — | 618-899 |
The FTIR of ITA-MMA copolymers’ results indicated that during the microwave process, the itaconic anhydride moieties were not disrupted in the copolymer backbone chain, which is in accordance with the previously reported data [
Thermogravimetric analysis of the prepared copolymers is shown in Table
Information derived from the TGA of the degradation of the EPMITA and DPMITA copolymers.
Copolymer code | Distribution of volatile ranges (temperature range) (°C) | Residue (%) | ||||||
---|---|---|---|---|---|---|---|---|
EPMITA 1-5 | 30-150 | 150-230 | 230-349 | 349-600 | 168 | 248 | 340 | 17.13 |
6.7% | 17.7% | 27.0% | 32.2% | |||||
EPMITA 1-10 | 30-142 | 142-229 | 229-339 | 339-600 | 228 | 387 | 377 | 18.88 |
4.0% | 12.4% | 26.6% | 37.9% | |||||
EPMITA 1-15 | 30-137 | 137-225 | 225-331 | 331-600 | 244 | 390 | 371 | 13.80 |
2.7% | 14.1% | 25.2% | 43.7% | |||||
EPMITA 1-20 | 30-99 | 99-215 | 215-342 | 342-600 | 254 | 399 | 394 | 12.13 |
0.7% | 13.8% | 25.7% | 47.7% | |||||
EPMITA 2-15 | 30-100 | 100-231 | 231-329 | 329-600 | 231 | 388 | 381 | 11.00 |
1.4% | 10.9% | 25.1% | 51.3% | |||||
EPMITA 2-20 | 30-100 | 100-235 | 235-329 | 329-600 | 236 | 390 | 385 | 9.75 |
1.1% | 12.9% | 23.0% | 52.9% | |||||
EPMITA 3-15 | 30-100 | 100-149 | 149-323 | 323-600 | 222 | 380 | 380 | 8.80 |
0.5% | 2.3% | 29.3% | 59.7% | |||||
EPMITA 3-20 | 30-100 | 100-326 | 326-600 | 253 | 387 | 390 | 7.29 | |
0.6% | 30.9% | 61.2% | ||||||
DPMITA 1-5 | 30-164 | 164-231 | 231-345 | 345-600 | 188 | 401 | 384 | 18.84 |
6.3% | 11.1% | 25.5 | 38.0% | |||||
DPMITA 1-10 | 30-199 | 199-257 | 257-350 | 350-600 | 140 | 408 | 370 | 16.49 |
20.4% | 12.1% | 14.4 | 36.5% | |||||
DPMITA 1-15 | 30-243 | 243-371 | 371-600 | 143 | 412 | 422 | 20.48 | |
12.5% | 20.3% | 46.6% | ||||||
DPMITA 2-5 | 30-200 | 200-342 | 342-600 | 200 | 396 | 400 | 20.30 | |
7.5% | 28.0% | 43.8% | ||||||
DPMITA 2-10 | 30-143 | 143-341 | 341-600 | 212 | 400 | 399 | 16.56 | |
11.5% | 22.7% | 47.3% | ||||||
DPMITA 3-5 | 30-130 | 130-238 | 238-329 | 329-600 | 238 | 382 | 384 | 12.56 |
5.5% | 4.8% | 22.4 | 53.1% | |||||
DPMITA 3-10 | 30-194 | 194-333 | 333-600 | 263 | 391 | 398 | 14.14 | |
1.8% | 25.3% | 54.7% |
TGA curves recorded for the different copolymers: (a) EPMITA 1-5 and DPMITA 1-5; (b) EPMITA 1-10 and DPMITA 1-10; (c) EPMITA 1-15 and DPMITA 1-15 showing the effect of the type of cross-linking agent used.
TGA curves recorded for the different copolymers: (a) EPMITA 1-15, EPMITA 2-15, and EPMITA 3-15; (b) EPMITA 1-20, EPMITA 2-20, and EPMITA 3-20; (c) DPMITA 1-5, DPMITA 2-5, and DPMITA 3-5; (d) DPMITA 1-10, DPMITA 2-10 and DPMITA 3-10 showing the effect of the monomer molar ratio used.
The EPMITA copolymers showed high thermal stability when using >10% (
On the other hand, the thermal stability of the DPMITA copolymers is affected by the copolymer composition as well as the percentage of cross-linking agent used. A significant increase in the thermal stability was observed upon increasing the ITA content with the onset temperature increasing from 140 to 212°C, reaching a maximum at 263°C for the DPMITA 1-10, DPMITA 2-10, and DPMITA 3-10 copolymers, respectively. The same results, obtained for DPMITA 1-5, DPMITA 2-5, and DPMITA 3-5, made clear that the thermal stability decreased upon increasing the percentage of cross-linking agent used.
The morphological structures of the copolymers EPMITA 1-15, EPMITA 2-15, and EPMITA 3-15, EPMITA 1-20, EPMITA 2-20, EPMITA 3-20 (Figure
SEM images of the different copolymers: (a) EPMITA 1-15, (b) EPMITA 2-15, (c) EPMITA 3-15, (d) EPMITA 1-20, (e) EPMITA 2-20, and (f) EPMITA 3-20 showing the effect of the monomer molar ratio, type, and percentage of the cross-linking agent used.
SEM images of the different copolymers: (a) DPMITA 1-5, (b) DPMITA 2-5, (c) DPMITA 3-5, (d) DPMITA 1-10, (e) DPMITA 2-10, and (f) DPMITA 3-10 showing the effect of the monomer molar ratio, type, and percentage of the cross-linking agent used.
In regard to series A (Figure
On the other hand, from series A to series B (Figure
In the case of using DVB as the cross-linking agent, stiffness structure was formed in all cases and there was no effect due to the monomer ratio or the percentage of cross-linking agent used on the morphology of the as-prepared copolymers [
According to the SEM images, EPMITA 1-15 and EPMITA 2-15 showed a porous structure. Therefore, both samples were selected to analyse the surface area and type of pores and pore volume by BET. The BET surface area and pore size distribution are displayed in Figure
(a) N2 adsorption/desorption isotherms and (b) pore size distribution by the BJH method.
The above-going discussions and the results obtained for EPMITA 1-15 and EPMITA 2-15 copolymers indicate that these possess a mesoporous and macroporous structure with average pore sizes of 26.6, and 25.3 nm, respectively. Hence, these obtained data could be useful for application in water purification technology.
Cross-linking has been used to improve the solubility, stiffness, mechanical strength, and rigidity of polymers for some potential applications. Itaconic anhydride-based copolymers were prepared with methyl methacrylate in the presence of two types of cross-linking agents, EDMA and DVB, via a microwave-assisted synthesis. The FTIR results indicated that the microwave process did not disrupt the itaconic anhydride moieties in the copolymer backbone chain. The formation of a cross-linked copolymer is favoured rather than a gel during the polymerization process upon increasing the amount of MMA in the copolymer. The EPMITA copolymers show high thermal stability when prepared using >10% (
The data used to support the findings of this study are available from the corresponding author upon request.
The author declares that there is no conflict of interest.
The authors would like to extend their sincere appreciation to the Deanship of Scientific Research at King Saud University, Saudi Arabia, for funding this work (RG-1436-005).