Synthesis and characterization of new soluble polyamides from Acenaphtohydrazinomercaptotriazole diamine

A diamine Acenaphtohydrazinomercaptotriazole (AHTD) was synthesized in one step from acenaphthoqinone and 4-amino-3-hydrazino-5-mercapto-1,2,4-triazole. The diamin was characterized by FTIR, 1HNMR, 13CNMR and melting point. Diamin was used to prepare novel polyamides. The low temperature solution polycondensation of diamin with tow aromatic and tow aliphatic diacid chlorides afforded diamin-containing polyamides with inherent viscosities of 0.38–0.47 dl/g in DMF at 25 °C. The polyamides were generally soluble in a wide range of solvents such as dimethylformamide(DMF), N-Methylpyrolidone(NMP), tetrachloroethane (TCE), dimethylsulfoxide(DMSO) and H2SO4. Thermal analysis showed that these polyamides were practically crustily and with Tg under 100 °C.


Introduction
Acenaphthoquinone is a quinone derived from acenaphthene.It is insoluble in water, but soluble in alcohol.It is used as an intermediate for the manufacturing of dyes, pharmaceuticals and pesticides.It is also used in chemical research as a drug and therapeutic agent.Triazole derivatives have been reported as a class of useful heterocyclic compounds, and have found widespread applications in the fields of agrochemicals and pharmaceuticals [1,2] .We have synthetized a diamin that produced of reaction of acenaphtochinon with Triazole derivatives and is used for production of thermally stable polyamides.Polyamides are characterized as high temperature resistant materials with a favorable balance of other physical and chemical properties [3] .Aromatic polyamides have the poor process ability due to their insolubility in common organic solvents and extremely high glass transition or melt temperature.The synthesis of soluble polyamides without deteriorating their excellent properties [4][5][6][7][8][9][10] .DSC studies of some polyamides [11,12] were reported in literature.We successfully prepared aromatic polyamides [13] , polyimides [14] , polyesters, polyquinoxalines, from a number of new functional monomers [15] .Thermally stable polymers have received extensive interest due to the increasing demands for high temperature polymers as replacements for ceramics and metals in the automotive, aerospace, and microelectronics industries.Aromatic polyamides are one of the most important classes of high performance polymers, because they possess excellent mechanical properties, thermal stability, chemical resistance, and low flammability.However, they encounter processing difficulties due to limited solubility in organic solvents and high glass transition or melting temperatures.It is a result of chain stiffness and intermolecular hydrogen bonding between amide groups.In this article, we report the synthesis of polyamides by low temperature solution polycondensation of diamin with tow aromatic and tow aliphatic diacid chlorides such as terephthaloyldichloride (TP), isophthaloyldichloride(IP), adipoylchloride(AP) and sebacoyldichloride (SC) .Physical properties of polymers including characterization, inherent viscosity, solubility, and thermal properties are also reported.

Materials and instruments
Acenaphthoqinone, 4-amino-3-hydrazino-5-mercapto-1,2,4-triazole and other reagents and solvents were purchased from Fluka and used without purification. 1HNMR and 13 CNMR spectra were recorded on a 500 MHz Bruker Advance DRX instrument using DMSO-d 6 as solvent and tetramethyl silane as an internal standard.FTIR spectra were recorded using a Bruker Vector 22 spectrometer on KBr pellets.The CHN-600 Leco analyzer was used for elemental analysis.Thermal gravimetric analysis (TGA) and differential scanning calorimetry (DSC) analysis were performed using Perkin-Elmer Pyris and Metler Tolledo 822 e , respectively.Inherent viscosity (η inh =Lnη rel /C) of polymers were determined for solution of 0.5 g/dl in NMP at 25 °C using an ubbelohde viscometer.Total sulfur was measured using Tanaka Model RX-360 SH.

Acenaphtohydrazinomercaptotriazoldiamine (AHTD)
The 1,2-dihydro-acenaphtylene-1,2-dione (1.82 g, 10 mmol) was dissolved in 25ml of ethanol and 1ml of conc.HCl and then added to a suspension of 4-amino-3hydrazino-5-mercapto-1,2,4-triazole (2.92 g, 20 mmol) in 25 ml of ethanol and 5 ml water.The mixture was stirred for 10 h at reflux temperature.The orange solid was filtered off, washed with ethanol and water and dried in a vacuum oven at 70 °C.A orange solid product was obtained in a 65% yield which starts to melt at 260 °C.
The chemical structure of diamine and its procedure is shown in Scheme 1.

Polyacenaphtohydrazinomercaptotriazolterephthalate (PA1)
A typical procedure for the preparation of polyamides is given in Scheme 2. A 100 ml two-necked flask equipped with a dropping funnel and gas inlet tube was charged with a mixture of AHTD (0.656 g, 2 mmol), 30 ml dimethylformamide (DMF) and triethylamine (0.8 ml). 2 mmol Diacidchloride (DC) (such as terephthaloyl chloride, isophthaloyl chloride, adipoyl chloride and sebacoyl chloride) dissolved in 20 ml DMF was added dropwise to the stirred solution at 0 °C under N 2 .The mixture was subsequently stirred at ambient temperature for 5 h under N 2 , and then it was poured into cold water.The orange solid product was separated by filtration and washed with NaHCO 3 solution.Then the solid product dried in vacuum oven at 70 °C.An orange solid product was obtained in a 86% yield which starts to melt at 280 °C.

IR, 1 HNMR and Elemental Analysis of diamine(AHTD)
The monomer, AHTD, was prepared according to the procedures which are given in the Scheme 1. IR, 1 HNMR and the results of elemental analysis are given in Table 1.
These regions of the IR spectra in Figure 1  AHTD using triethylamine as catalyst.The reactions were carried out in DMF solution of the diacidchloride and AHTD in a nitrogen atmosphere and at room temperature.The polymerizations proceeded in homogeneous solution and the yields of the polyamides were quantitative.The elemental analysis values of all the polyamides, Table 1, were generally in good agreement with the calculated values of proposed structures.As representative example,    the complete elemental analysis of PA1 was as follows: C, 50.70% (51.02% calculated); H, 2.82% (3.21%); N, 29.57% (28.58%).The polyamides were also characterized by IR and NMR spectrometers.The presence of amide bands at ca. 3430 cm -1 (N-H stretching), 1790 cm -1 (C=O stretching), 1631 cm -1 (N-H bending and C-N stretching) and 910 cm -1 (C-S), in the IR spectra in Figure 4 for PA1 and amidic proton at ca. 12.5 ppm in the NMR spectra of PA1 in Figure 5 confirmed the amidic structure of polymers.
The limiting viscosity number [η] of polyamides was determined for extracted and dried polymers in DMF, depending on the solubility of the polyamide.For the same or similar type of linear polymers the [η] value is proportional to the molecular mass.The inherent viscosities of polyamides (PA1-PA4), obtained in DMF were in the  range of 0.38-0.47dl/g that revealed reasonable molecular weights.The limiting viscosity number [η] of aromatic polyamides is less than aliphatic polyamides.
One of the major objectives of this study was producing modified polyamides with improved solubility.The solubility of these polyamides was determined for the powdery samples in excess solvents and the results are listed in Table 2.
All the polyamides were readily soluble in common polar aprotic solvents without need for heating.Also, by heating they were soluble in a less efficient solvent such as THF.The good solubility behavior of most prepared polyamides can be explained through the enhancement of solubility induced by the side biphenyl groups of the diamine moiety.The thermal behavior of polyamides was studied by DSC and TGA.. Thermal properties of the prepared polyamides were evaluated by means of DSC and TGA.Representative DSC and TGA thermograms are shown in Figures 6, 7, 8 and 9 for two aromatic and aliphatic polyamides(PA2,PA3).
The DSC curves of Polyamides(PA2,PA3) were shown the glass transition temperature of these polymers at 65 °C and 55 °C and cristallinity temperature of both polymers at 251 °C and the melt temperature of polymers at 330 °C and 310 °C respectively.The DSC curves showed that the aliphatic polyamides have lower glass transition temperature such as aromatic polyamides and they have certainly melt temperature less than aromatic polyamides.
The thermal stability of polyamides was also evaluated by TGA.The temperatures of the 10%, 25% and 50% weight loss and the remained polyamides at 600 °C in nitrogen atmosphere were given in Table 3.All the polymers were stable up to 200 °C in nitrogen and show almost the same stability.We found that these polyamides did not show obvious weight losses until the temperature reached 200 °C in nitrogen, implying that no thermal decomposition occurred.However, as the temperature over 200 °C, the polymers showed a rapid thermal decomposition.The 10% weight loss of all polymers was in temperature range of 180-230 °C.The 25% weight loss of all polymers was in temperature range of 290-320 °C.The 50% weight loss of all polymers was in temperature range of 340-450 °C.The polyamides (PA1,PA2) remained 42-60% of the original weight at 600 °C in nitrogen and the polyamides (PA3,PA4) remained over 16-38% of the original weight at 600 °C in nitrogen.Two of the polyamides(aliphatic) exhibited a more weight loss at the same temperature and they have a short char yield against aromatic polyamides.

Conclusion
A series of polyamides were prepared from the reaction of two aromatic and two aliphatic diacid chlorides with a diamine AHTD.The molar ratio of diacid chloride to the AHTD was 2:2 and the reaction was carried out at ambient temperature for 5 h under N 2 atmosphere.The polyamides were fully characterized and their thermal properties were studied.Two of the polyamides(aliphatic) exhibited a more weight loss at the same temperature and they have a short char yield against aromatic polyamides.The introduction of aromatic side groups in structure of the diamine resulted   in crystalline polyamides that the degree of crystallinity has a big influence on hardness, density, transparency and diffusion.The polyamides have very good solubility in aprotic solvents such as DMF and generally, the solubility of aromatic polyamides were better in selected solvents.Aliphatic polyester hopes of higher inherent viscosity and thus had a higher molecular weight.The glass temperature of the aliphatic polyamides was lower than aromatic polyamides but unlike crystalline temperature and melting temperature are close together and the differences were not significant.

1 .Scheme 2 .
Scheme 1.The procedure for the preparation of Diamine.
Temperature.T c cristallinity Temperature .T m Melting temperature.a 10% weight loss.b 25% weight loss.c 50% weight loss.d Char yield percent at 600 °C, obtained from TGA. e Measured in DMF at 25 °C (c=0.5 g/dl).

Table 1 .
Spectra data, elemental analysis results and the yield of polyamides.

Table 3 .
Thermal analysis, viscosity and yield of the polyamides.