New Optically Active and Thermally Stable Poly ( amide-imide ) s Containing N , N ’-( Bicyclo [ 2 , 2 , 2 ] oct-7-ene-2 , 3 , 5 , 6-tetracarboxylic )-bis-L-Alanine and Aromatic Diamines : Synthesis and Characterization

Cinco novas poliamidas-iminas (PAIs) oticamente ativas 6a-e foram preparadas pela reação de policondensação direta da N,N ́-(biciclo[2,2,2]octa-7-eno-2,3,5,6-tetracarboxila)-bis-L-alanina 4 com várias diaminas aromáticas 5a-e usando solventes polares apróticos como a N-metil-2pirrolidona (NMP). Neste procedimento, trifenil fosfito (TPP) e piridina foram usados como agentes de condensação para formar poliamidas-imidas através dos sais de N-fosfônio-piridina. Todos os polímeros foram obtidos com rendimentos quantitativos com uma viscosidade intrínseca entre 0,29-0,46 dL g-1, sendo altamente solúveis em solventes polares apróticos como N,N-dimetil acetamida (DMAc), N,N-dimetilformamida (DMF), dimetil sulfóxido (DMSO), N-metil-2pirrolidona (NMP) e ainda em solventes como o ácido sulfúrico. Os compostos foram caracterizados por espectroscopia de RMN H, espectroscopia no infravermelho, análise elementar, viscosidade intrínseca, testes de solubilidade, rotação específica e as propriedades térmicas desses polímeros foram investigadas usando técnicas termogravimétricas de análise (TGA e DTG).


Techniques
1 H NMR and 13 C NMR spectra were recorded on a Bruker 300 MHz instrument, (Germany).Fourier transform infrared (FTIR) spectra were recorded on Galaxy series FTIR 5000 spectrophotometer (England) as solid by using KBr pellets.Vibration transition frequencies were reported in wave number (cm -1 ) and band intensities were assigned as weak (w), medium (m), shoulder (sh), strong (s) and broad (br).Inherent viscosities were measured by a standard procedure using a Technico Regd Trad Mark Viscometer.Specific rotations were measured by an A-Kruss polarimeter.Thermal Gravimetric Analysis (TGA and DTG) data for polymers were taken on a Mettler TA4000 System under N 2 atmosphere at rate of 10 °C min -1 .Elemental analyses were measured by Vario EL equipment by Arak University.

Polymer synthesis
As a typical example, PAI 6c was prepared as follows: Into a 50 mL round-bottom flask with a stirring bar were placed (0.100 g, 0.326 mmol) diimide-diacid 4, (0.065 g, 0.326 mmol) of 3,3´´-diamino diphenyl sulfone 5c, 0.10 g of calcium chloride, 1.0 mL of NMP, 0.8 mL of triphenyl phophite and 0.3 mL of pyridine.The mixture was stirred at room temperature for 2 h and then was heated while stirring at 120-130 °C for 8 h.At the end of the reaction, for quenching growth of the polymer chain, the polymer solution was slowly trickled into a stirred methanol, giving a stringy precipitate.Then polymeric product was washed with hot methanol, collected by filtration and dried at 80 °C for 12 h under vacuum to leave 0.163 g (91%) of solid polymer 6c.
The chemical structure and purity of diimide-diacid 4 were proved by using elemental analysis, 1 H NMR, 13 C NMR and FTIR spectroscopy.The measured results in elemental analyses were closely corresponded to the calculated ones, demonstrating that the expected compound was obtained.Figure 1 displays FTIR spectrum of diimidediacid 4. Peaks appearing at 2400-3400 cm -1 (acid O-H stretching), 1770 cm -1 (C=O asymmetric imide stretching), 1705 cm -1 (C=O acid and symmetric imide stretching), 1396 and 675 cm -1 (imide characteristic ring vibration) confirmed the presence of imide rings and carboxylic groups in this compound.
The 1 H NMR spectrum of diimide-diacid 4 showed in Figure 2. H(a) protons relevant to O-H carboxylic groups, H(b) protons relevant to olefin hydrogens that appeared in region of 5.95-5.98ppm.Peaks in the region 4.50-4.57ppm as a quartet were assigned to the CH(c) proton which is a chiral center.
The 13 C NMR spectrum of diimide-diacid 4 showed 7 signals including C(b) in carboxylic group that appeared in region of 176.82 ppm, C(d) was relevant to chiral carbon atom that appeared in region of 47.55 ppm (Figure 3).Synthesis and some physical properties of PAIs 6a-e are summarized in Table 1.These polymers have inherent viscosities in range of 0.29-0.46dL g -1 .All of the resulting polymers show optical rotations and have optical activities.Results show that PAIs 6b and 6c have higher inherent viscosities in comparing to other PAIs because they have  a rigid and polar moiety in the diamine structure such as sulfone moiety (Table 1).

Polymer characterization
The structures of these polymers were confirmed as PAIs by mean of FTIR, 1    The representative FTIR spectrum of PAI 6e was shown in Figure 4.The polymer exhibited characteristic absorption bands at 1707-1774 cm -1 to the imide ring (asymmetric and symmetric C=O stretching vibration) and 1384 cm -1 (C-N stretching vibration).The absorption bands of amide groups appeared at 3286 cm -1 (N-H stretching).
Figure 5 displays 1 H NMR spectrum of PAI 6d.Peak at 9.60 ppm related to NH of amide groups in the polymer chain, aromatic protons related to 1,4-phenylene appeared in the region of 7.41 ppm and the peak in the region of 6.06 ppm related to olefin protons.
The elemental analyses of the resulting PAIs 6a-e were in good agreement with the calculated values for the proposed structure (Table 3).
The solubility of PAIs 6a-e was investigated by 0.01g of polymeric sample in 2.0 mL solvent.All of the polymers are soluble in organic solvents such as N,N-dimethyl acetamide (DMAc), N,N-dimethyl formamide (DMF), dimethyl sulfoxide (DMSO), NMP (N-methyl-2pyrrolidone), sulfuric acid and are insoluble in solvents such as chloroform, methylene chloride, methanol, ethanol and water (Table 4).

Thermal properties
The thermal properties of PAIs 6a and 6c were investigated by TGA and DTG in a N 2 atmosphere at a heating rate of 10 °C min -1 as model for prepared polymers and the thermal data are summarized in Table 5 (Figure 6).The initial decomposition temperatures of 5% and 10% +) and insoluble (-) at room temperature.weight losses (T 5 and T 10 ) and the char yield at 600 °C are summarized in Table 5.These polymers exhibited good resistance to thermal decomposition up to 320 to 340 °C in nitrogen and began to decompose gradually above those temperatures.T 5 for these polymers ranged from 320 to 340 °C and T 10 for two polymers ranged from 345 to 355 °C and the residual weights for these polymers at 600 °C ranged from 38 and 58% in nitrogen.Results show that PAI 6c containing sulfone moiety has higher thermal stability in comparing to PAI 6a because this polymer has a rigid and polar moiety in the diamine structure such as sulfone moiety (Table 5).

Conclusions
A new series of PAIs 6a-e containing bicyclo[2,2,2] oct-7-ene-2,3,5,6-tetracarboxylic diimide were synthesized by direct polycondensation reaction of N,N´-(bicyclo [2,2,2]  oct-7-ene-2,3,5,6-tetracarboxylic)bis-L-alanine 4 with various aromatic diamins 5a-e using triphenyl phosphite, NMP, calcium chloride and pyridine as condensing agents.The high char yields of these polymers showed that the introduction of bicyclo and aromatic rings into the polymer backbone increased the thermal stability and solubility in polar amidic solvents.Since these optically active polymers have amino acid in the polymer architecture and they are expected to be biodegradable.Optically active and thermal stability properties can make these polymers attractive for practical applications such as processable highperformance engineering plastics used as chiral stationary phase and chiral media for asymmetric synthesis.

Table 1 .
H NMR spectroscopy and elemental analyses.FTIR spectroscopy of all PAIs are listed in Table 2. Vol. 20, No. 10, 2009 Synthesis and some physical properties of PAIs 6a-e

Table 2 .
FTIR Characterization of PAIs

Table 5 .
Thermal behavior of PAIs 6a and 6c Temperature at which 5% and 10% weight loss was recorded by TGA at heating rate of 10 °C min -1 in N 2 respectively. .c Percentage weight of material left undecomposed after TGA analysis in 600 °C.