SYNTHESIS AND CHARACTERIZATION OF NEW HEAT RESISTANCE AND ORGANOSOLUBLE POLY(ETHER-AMIDE)

New series of olefinic poly(ether-amide)s (OPEA)s 6a-f was synthesized from 4,4′-bis(1,4diphenoxybutane)diacrylic acid 4 and aromatic diamine 5a-f via a direct polycondensation reaction. The resulting polymers were characterized by Fourier transform infrared spectra (FTIR), nuclear magnetic resonance (HNMR), solubility test and inherent viscosity. The thermal properties of the polymers 6a-c were investigated by thermogravimetric analysis (TGA). Polymer 6c due to presence of SO2 group as a polar group shows better thermal properties compare with polymer 6a and 6b.


INTRODUCTION
Aromatic polyamides are noted for high transparency, excellent mechanical properties, heat resistance, good char yield, low flammability, good barrier properties, and outstanding strengthto-weight ratios and solvent resistance [1][2][3][4]; however, they are difficult to process because of limited solubility and high glass transition (T g ) [5][6][7].The processing of these polymers has been greatly hindered because they lack softening or melting property at usual processing temperature, and they tend to decompose at the softening temperature.Many efforts have been made to create structurally modified aromatic polyamides having better solubility and processability.It is known that the solubility of polyamides is often increased when flexible bonds such as [-CH 2 -, -O-, -SO 2 -, -C(CF 3 -) 2 ], bulky pendent groups, polar components or large pendent groups are incorporated into the polymer backbone due to the altering crystallinity and intermolecular interactions [8][9][10][11][12][13], synthesis of polyamides with noncoplaner unit in the polymer chains [14], preparation of copolymers such as poly(amide-imide)s [15][16][17][18], poly(esterimide)s [19], poly(amide-ester-imide)s [20] and the introduction of bulky side groups into the polymer chains [21][22][23] resulted a series of modified polyamides.
It has been recognized that the incorporation of aryl-ether linkages generally imparts an enhanced solubility, processability, and toughness of aromatic polyamides without substantial diminution of thermal properties [24].Aromatic polymers that contain aryl ether linkages generally have lower glass transition temperatures, greater chain flexibility, and tractability in compared to their corresponding polymers without these groups in the chain [25][26][27].The lower glass transition temperatures and also improved solubility are attributed to the flexible linkages that provide a polymer chain with a lower energy of internal rotation [28].

Techniques
The Fourier transform infrared spectra (FTIR) were measured using the Bruker Vertex 80 V spectrometer over the wavenumber range of 600-4000 cm -1 .NMR measurements were performed with a Bruker 300 MHz and Bruker 500 MHz spectrometer.DMSO-d 6 was used as the solvent and the solvent signal was used for internal calibration (DMSO-d 6 : δ ( 13 C) = 39.6 ppm, δ ( 1 H) = 2.5 ppm).Inherent viscosities were measured by a standard procedure by using a Technico Regd Trad Mark Viscometer.Thermal gravimetric analysis (TGA) data for the polymers were taken on a Mettler TA4000 System in the range between room temperature and 800 °C at a heating rate of 10 ºC/min in nitrogen atmosphere.

Monomer synthesis
Dicarboxylic acid 4 containing aryl ether and methylene group was synthesized by using two step reactions.At first 4,4′-bis(1,4-diphenoxybutane)dialdehyde 3 was prepared from the reaction of one equimolar 1,4-dibromobutane 2 and two equimolars 4-hydroxybenzaldehyde 1.Then dialdehyde compound 3 was reacted with malonic acid at presence of catalytic amount of morpholine under a solvent free condition.The chemical structure and purity of dicarboxylic acid compound 4 were confirmed by FTIR, 1 H-NMR, and 13 C-NMR spectroscopy.

Polymer characterization
The structure of polymer was confirmed by 1 H-NMR and FTIR spectroscopies.FTIR data of OPEAs 6a-f exhibited characteristic absorption bands around 1670 cm -1 for the amide group (C=O stretching vibration) and the N-H stretching absorption bands of amide groups around 3280 cm -1 (N-H stretching).The 1 H-NMR spectrum of polymer 6e showed peaks that confirm its chemical structure (Figure 1).The aromatic and olefinic protons related to polymer backbone appeared in the region of 6.6-7.8 ppm.The protons related to methylene group appeared at 1.9 and 4.1 ppm and the peak in the region of 10.5 ppm is assigned for NH of the amide groups in the polymer chain.

Solubility test
One of the main objectives of this study was producing modified polyamides with improved solubility.The incorporation of monomers with flexible group such as ether moieties in the polymer backbone, led to these polymers have good solubility in various solvents, especially organic aprotic solvents.The solubility of OPEAs 6a-f was investigated as 0.01 g of polymeric sample in 2 mL of solvent.Remarkably, all of OPEAs were easily soluble at room temperature in aprotic polar solvents such as N-methyl-2-pyrrolidone (NMP), N,N-dimethylacetamide (DMAc), N,N-dimethylformamide (DMF) and insoluble in solvents such as acetone, chloroform, ethanol and methanol (Table 2).

Thermal properties
Thermal stability of the OPEA 6a-c determined under inert atmosphere is shown in Figure 2.
The initial decomposition temperatures of 5% and 10% weight losses (T 5 and T 10 ) and the char yield at 800 °C are summarized in Table 3. Thermal decomposition temperatures of the polymers were found in the range 237-241 °C.Compared with the thermal decomposition behavior of OPEA 6a, OPEA 6b and 6c with two benzene rings show higher 5 wt% and 10 wt% and delay the decomposition.The weight retained at 800 °C shows higher char residue at high temperature and improves significantly with percent of SO 2 group.

CONCLUSIONS
In this article, an efficient method for the synthesis of 4,4′-bis(1,4-diphenoxybutane) diacrylic acid 4, containing ether and olefinic groups, has been developed under solvent free condition in presence of morpholine as a catalyst.New poly(ether-amide)s with good inherent viscosity were prepared by the direct polycondensation reaction of the synthesized diacid and aromatic diamine 5a-f.The results presented herein also clearly demonstrate that incorporating the ether group into the polymer main chain as well as combination of the wholly aromatic backbone and several functional groups remarkably enhanced the solubility in organic solvents of the new polymers.The thermal stability and char residue of the OPEA 6c due to presence SO 2 have been increased as compared with the OPEA 6a.These properties could make these OPEAs attractive for practical applications such as processable high-performance engineering plastics.
a Measured at a concentration of 0.5g/dL in DMF at 25˚C.b B = Brown, C = Cream, Y= Yellow.

Table 3 .
Thermal and fire measurements of OPEAs 6a-c.
a Temperature at which 5% or 10% weight loss was recorded by TGA at a heating rate of 10 ˚C/min under N2.b Weight percentage of material left after TGA analysis at a maximum temperature of 800 ˚C.