A new difunctional monomer N,N'-[bis(4,4'-hydroxypropyl methacrylate phenyl ester) pyromellitimide] (BHPMEPM), was synthesized by the reaction of the bis(4-carboxyphenyl)-N,N'-pyromelli- timide acid (diacid-diimide), and two molar equivalents of glycidylmethacrylate (GMA). The reaction was carried out by microwave radiation. The presence of difunctional groups, double bond groups, makes the monomer a potential material for obtaining thermosetting product. The curing and thermal stability of the crosslinked products were studied by differential scanning calorimetry (DSC) and thermal gravimetric analysis (TGA) techniques. The difunctional monomer and its thermoset polymer were characterized by FT-IR, 1 H-FT-NMR and CHN elemental analysis.
Due to their unique combination of properties like good dielectric strength and dimensional stability, Polyamides (PIs) as thermostats resins are constantly attract a wide interest [
4-Aminobenzoic acid (p-ABA, Fluka), pyromellitic dianhydride (PMD, Aldrich), glycidylmethacrylate (GMA, Aldrich), triethylbenzylammonium chloride (TEBAC, Fluka), were purchased as analytical grade products and used as received. Pyridine (py, Fluka), was dried over solid KOH and fractionally distillated, dimethylformamide (DMF), was dried over MgSO4 followed by distillation under reduced pressure. All organic solvents were analytical grade products and were used as received or purified by distillation before use.
1H-NMR spectra were obtained on a 500 MHz FT-NMR spectrometer (Bruker Instruments, model Avance-III 500, Germany) at room temperature using DMSO-d6as a solvent and TMS as an internal standard. FT-IR spectra were obtained with a JASCO model FT/IR 4200 in the 4000 - 400 cm−1 range on KBr pellets. Thermogravimetric analysis and differential scanning calorimetry (TGA and DSC) data were taken on a NETZSCH STA 449F3 System under N2 atmosphere at a rate of 10˚C/min for DSC and TGA. Elemental analysis were performed with a Perkin-Elmer 2400 CHN analyzer.
The bifunctional monomer N,N'-[bis(4,4'-hydroxypropyl methacrylate phenyl ester) pyromellitimide] was synthesized in two steps from bis(4-4' carboxyphenyl)-N,N'-pyromellitimide acid (diacid-diimide) and glycidyl methacrylate (described below and shown in Scheme 1).
This compound was prepared and characterized according to our previous works [
Mixtures of 4.563 g (1 mmol) of diacid-diimide, 2.843 g (2 mmol) of GMA were located in 100 mL RBF provided with a condenser and a magnetic stirrer, overlayered with 50 mL dry DMF. The RBF was flashed with nitrogen and microwave irradiated (power input: 600 W) for 15 minutes. The small amount of unreacted diacid- diimide was removed from the reaction mixture by filtration. The effluent obtained was evaporated under reduced pressure to its half original volume and the viscous product precipitated by distilled water. The precipitate was filtered, washed twice with 100 mL warm distilled water and dried under vacuum at 45˚C for 48 h. Yield =
Scheme 1. Synthetic route of the compound BHPMEPM.
91%. Anal. Calcd. for C38H32N2O14: C, 61.61; H, 4.35; N, 3.83. Found: C, 61.56; H, 4.41; N, 3.87%. IR (KBr)
0.2 g of BHPMEPM was dissolved in 5 mL of DMSO at room temperature, the solution was cast on a quartz plate, and then dried in vacuo. The isolated monomer films were cured at 180˚C for 2 h, in vacuo. After curing, the film was used for the IR and TG.
Diacid-diimide was synthesized from condensation reaction of aquimolar of pyromellitic dianhydride (PMD) with two aquimolar of p-amino benzoic acid (p-ABA) in a mixture of glacial acetic acid and pyridine using microwave irradiation.
The difunctional monomer N,N'-[bis(4,4'-hydroxypropyl methacrylatephenyl ester) pyromellitimide] (BHP- MEPM) was obtained through the reaction between aquimolar of bis(4-carboxyphenyl)-N,N'-pyromellitimide acid (diacid-diimide) and two aquimolar of glycidylmethacrylate (GMA) (Scheme 1).
The chemical structure of the bifunctional monomer BHPMEPM was confirmed by FT-IR, 1HNMR spectroscopy and elemental analysis. In the FT-IR spectrum (
Further characterization was performed with 1H NMR. In 1H NMR spectrum (
The thermal behavior of the polymerization reaction of bifunctional monomer BHPMEPM was monitored by DSC scanning. The thermogram of the BHPMEPM is presented in (
It can be noticed that BHPMEPM shows one reaction exotherm depending on the reactivity of methacrylic two double bonds.
The curing reaction starts at around 163˚C with a maximum of the exothermic peak at 180.2˚C. At about 195˚C, the curing is complete where the absence of exotherm indicates no post curing. The difunctional monomer BHPMEPM was crosslinked under 180˚C for 2.0 h to give the thermoset resin (Scheme 2).
Scheme 2. Probable crosslinking mechanism of BHPMEPM.
The thermal stability and thermal degradation behavior of the cured bifunctional monomer BHPMEPM were examined by analysis of the thermogravimetric (TG-DTG) curve (
The TG of cured monomer BHPMEPM has typical pattern of thermograms, involved three steps of weight loss from 25˚C to 800˚C. The first weight loss for cured product was observed from 230˚C to 386˚C with 37.47% loss weight. The second weight loss for the polymer occurred at the temperature range from 452.9˚C to 571.3˚C with 16.14% loss weigh. Finally, the third weight loss for the polymer occurred at the temperature range from 571.3˚C to 730˚C with 12.47% loss weigh. This result is comparable with the thermal analysis of poly(glycidyl methacrylate) which undergoes one step of weight loss, between 140 and 450˚C [
The polymer shows good solubility in aprotic polar solvents such as NMP, DMAc, DMF, and DMSO, while insoluble with common organic solvents such as tetrahydrofuran, chloroform, acetone and benzene. The polymer had good transparency and its inherent viscosity (η inh) is 0.82 dL/g.
The diacid-diimide was used as a building block of poly(imide-ester) by its reaction with glycidylmethacrylate to produce a new bifunctional monomer. The structure of this monomer was confirmed by FT-IR, 1H FT-NMR, and elemental analysis. The curing reaction of this bifunctional monomer was monitored by DSC scanning which shows that one reaction exotherm represents the crosslinking cured product depending on the reactivity of methacrylic two double bonds with a maximum of the exothermic peak at 180.2˚C. The cured product shows good thermal properties and good solubility in aprotic polar solvents. The crosslinked products can be used as moulding compounds and encapsulating materials in electric or electronic industry.
Habib Saedi, (2016) Synthesis and Polymerization of N,N'-[Bis(4,4'-Hydroxypropyl Methacrylate Phenylester) Pyromellitimide] Thermoset Polymer by Microwave Irradiation. Advances in Chemical Engineering and Science,06,183-189. doi: 10.4236/aces.2016.62019