Synthesis and Characterization of New Aromatic Co-Polyamides

Thermal characteristics are very important for all polymers processed by moulding, injection or spinning. This applies not only to the melting temperature, but also the temperature of decomposition, the crystallization temperature and other characteristics. In addition, the enthalpies of melting and crystallization are important for semi-crystalline polymers as well. The DSC study of all components of blends (used for any product prepared via melting) therefore gives basic information about the components' future behaviour in the blend and during processing. Some properties of homopolymers are not always satisfying for their application in certain fields. Copolymer monomer based on a certain monomer with some amount of another, functional co-monomer may have specific characteristics which predestine this copolymer as raw material for products with better properties, or as an additive for homopolymer and may thus improve the properties of the product. Copolymers are able to improve many properties, including thermal properties. Copolymer has one great advantage, good compatibility with relevant homopolymers and from this point of view the deterioration of the blend properties is lower. Semi-crystalline (block) copolymers can co-crystallize with homopolymers, several type of crystals with various sizes and levels of perfection Synthesis and Characterization of New Aromatic Co-Polyamides


crystals with
various sizes and levels of perfection

can be formed and blocks of copolymer can create their own crystallites 4,5 .

During the copolyamide formation both mechanisms are applicable, but different to such an extent that there are formed block rather than statistic copolyamides 6 .

In the present paper the synthesis of a new types of aromatic Co-polyamides from various aliphatic and aromatic dicarboxylic acid (e.g., adipic acid, phthalic acid, terephthalic acid and 4-phenylenediacrylic acid) with new aromatic diamines, has been reported whose light scattering a d dilute solution behavior have been published elsewhere 7,8 .The polycondensation is carried out in the presence of triphenyl phosphite (TPP) in N-methyl-2-pyrrolidinone (NMP), pyridine mixture, containing 3 wt.% LiCl by the method of Yamazaki et al. 9 .Because of the low solubility of Co-polyamides, the polycondensation reaction terminates quickly and results in low molecular weight products.In order to do away with this problem, the polycondensation is carried out in the pres nce of LiCl 10,11 .

Differential scanning calorimetry (DSC) were measurements by DSC 131 Evo, Setaram, (France) using a heating rate of 10 °C/min in N2 atmosphere within the temperature range of (30-600 °C).The sample weight used approximately (10 mg ) mg.The peaks are used to determine the thermal properties of the samples.The solubility of the polymers was determined with (0.0 g) of a Co-polymer in (2 mL) of a solvent.

N-Methyl-2-pyrrolydinone (NMP) from (ALFA-PRODUCTS); absolute methanol, acetic acid, lithium chloride, palladium on cha coal 10 %, from (BDH, England); dichloromethane from (Biosolve); ammonium acetate, malonic acid and adipic acid from (Chem-supply).Hydrochloric acid, salicylaldehyde, from (HiMedia); diethyl ether from (IGCC, England); aniline, 3-chloroaniline, 2-bromoaniline, calcium chloride, benzaldehyde, 2,6-diamino pyridine, dimethyl sulphoxide (DMSO), glacial acetic acid, m-cresol, N,N-dimethylacetamide, 1,4-phenylene diamine, phthalic acid, terephthalic acid, piperidine, pyridine, terephthalaldehyde, triphenyl phosphite (TPP), tetrahydrofurane (THF), all from (MERCK); absolute ethanol from (Scharlab S.L); acetone, p-nitroacetophenone, all from (ALDRICH); N,N-dimethylformamide (DMF) from (Sinopharm Chemical Reagent); and hydrazine monohydrate from (THOMAS-BAKER).


Synthesis of monomers


Synt

sis of 4-phen
l-2,6-bis(4-nitrophenyl)pyridine (PNPP):

In a round-bottomed flask (150 mL) equipped with a reflux condenser, a mixture of benzaldehyde (1.6 g, 15 mmol), p-nitro acetophenone (5 g, 30 mmol), ammonium acetate (15 g) and glacial acetic acid (37.5 mL) was refluxed at 140-142 °C for 2 h.Upon cooling, crystals separated, which were filtered and washed first with acetic acid (50 %) and then with cold ethanol.These dark yellow crystals were recrystallized from absolute ethanol and then dried at 60 °C under vacuum 12,13


Scheme-I: Synthesis of [PNPP]


Synthesis of 4-phe yl-2,6-bis(4-aminophenyl)pyridine (PAPP) [M1]:

(2 g, 5 mmol) of the (PNPP), 0.2 g of 10 % Pd/C and 100 mL of ethanol were introduced into a threenecked flask to which 20 mL of hydrazine monohydrate was added dropwise over a period of 1 h at 85 °C.After completing the addition, the reaction was continued at reflux temperature for another 4 h.To the suspension, 40 mL of THF was added to re-dissolve the precipitated product and refluxing was continued for 1 h.The mixture was filtered to remove the Pd-C and the filtrate was poured into water.The product was filtered off, washed with hot water and dried in vacuum 14,15


Scheme-IV: Synthesis of M3

The other diamino compounds were prepared by the same procedure as above using 3-chloro aniline with salicylaldehyde (M5), 2-bromo aniline with salicylaldehyde (M6), 3-chloro aniline with acetone (M7), 2-bromo aniline with acetone

8), respectively, are
hown in (Table -


Synthesis of 4-phenylenediacrylic acid [ PPDAA]:

In a 100 mL round-bottomed flask were added terephth-alaldehyde (3.48 g, 26 mmol), malonic acid (8.27 g, 94 mmol) to 30 mL of pyridine containing small amount of piperidine.The reaction mixture was stirred for 2 h at 45 °C, 4 h at 80 °C and 3 h at 110 °C, respectively.The solution was poured into large amount of distilled water and neutralized with 10 % HCl to obtain white precipitate.The precipitate was filtered, washed with water, acetic acid and acetone and then

ried in a vacuum oven at room
emperature 18 to give 5.1 g (90 % wt) of white crystals; m.p. 222-225 °C (Scheme-IX).
C H C H H O O C C H C H C O O H Scheme-IX: Structure of PPDAA

Synthesis of Co-polyamides [CoP1-CoP6]:

A typical procedure was described as follows.In a three-necked flask equipped with a reflux condenser and N2 inlet, dicarboxylic acid and diamines (Table -2) were added.Then (2 g) dried lithium chloride, (14 mL) N-methyl-2-pyrrolidinone, (2.8 mL) pyridine and (2.8 mL) triphenyl phosphite were charged.The resulting mixture was reacted at 120 °C for 2 h under the nitrogen atmosphere.After the polymerization, the viscous mixture was poured into (200 mL

methanol.The Co-polymer was filtered and washed by met
anol and hot water and then dried at 100 °C for 12 h in vacuum 19 (Scheme-X and XI).


RESULTS AND DISCUSSION

The FTIR spectrum of (PNPP) indicated absorption band at (1500 cm -1 ), (1340 cm -1 ) to (-NO 2 ) asymmetric and symmetric stretching, respectively, absorption bands around (1676-1622 cm -1 ) show the presence of the aromatic ring and (1550-1520 cm -1 ) to heteroaromatic ring (C=N).

I

ppm (s, 2H ) for N-OH g
oup.

The FTIR spectrum of (M5) indicated absorption bands at (3415 cm -1 ) to (-NH2 group), absorption band at (3376 cm -1 ) to (-OH group), (3103 cm -1 ) to (aromatic -CH stretching), (2932 cm -1 ) to (aliphatic -CH stretching) and absorption bands around (1614-1521 cm -1 ) show th presence of the aromatic ring and (552 cm -1 ) to (C-Br).The characteristic absorption of (C=O aldehyde) disappeared.

1 H NMR spectrum of (M5), assigns the following chemical shifts; δ (2.5) ppm for DMSO, δ(6.2) ppm (s, 1H) for C-H group, 6.0 (s, 4H) for NH2 group, δ(6.2 -8.9) ppm (s, 10H) for ArH group, 5.7 (s, 1H, OH) group.

The TIR spectrum of (M6) indicated absorption bands at (3425 cm -1 ) to (-NH2 group), absorption band at (3100 cm -1 ) to (-OH group), (3107 cm -1 ) to (aromatic -CH stretching), (2918 cm -1 ) to (aliphatic -CH stretching) and absorption bands around (1608-1510 cm -1 ) show the presence of the aromatic ring and (725 cm -1 ) to (C-Cl .The characteristic absorption of (C=O aldehyde) disappeared.

The FTIR spectrum of (M7) indicated absorption bands at (3415 cm -1 ) to (-NH2 group), absorption band at (3300 cm -1 ) to (-OH group), (3100 cm -1 ) to (aromatic -CH stretching), (2932 cm -1 ) to (aliphatic -CH stretching) and absorption bands around (1614-1523 cm -1 ) show the presence of the aromatic ring nd (554 cm -1 ) to (C-Br).The characteristic absorption of (C=O aldehyde) disappeared.

The FTIR spectrum of (CoP1) indicated absorption bands at (3378 cm -1 ) to (-OH group), (3208 cm -1 ) to (aromatic -CH stretching), (2901 cm -1 ) to (aliphatic -CH stretching), absorption bands around (1610-1536 cm -1 ) show the presence of the aromatic ring, the sharp band at (1616 cm -1 ) to (C=O amide) and (1544 cm -1 ) to vinyl segment. 1 H NMR spectrum of (CoP1), assigns the following chemical shifts; δ (2.5) ppm for DMSO, δ (8.5) ppm for HC=CH δ (6.3-8.6)ppm (s, 10H ) for ArH group, 5.7 (s, N-H) group.

The FTIR spectrum of (CoP2) which indica ed absorption bands at (3335 cm -1 ) to (-OH group), (3123 cm -1 ) to (aromatic -CH stretching), (2915 cm -1 ) to (aliphatic -CH stretching), absorption bands around (1603-1511 cm -1 ) show the presence of the aromatic ring, the sharp band at (1621 cm -1 ) to (C=O amide), (1524 cm -1 ) to vinyl segment and (808 cm -1 ) to (C-Cl).

1 H NMR spectrum of (CoP2), assigns the following chemical shifts; δ (2.5) ppm for DMSO, δ (6.2) ppm (s, 1H) for C-H group, 6.0 (s, 4H) for NH2 group, δ (6.2 -8.9) ppm (s, 10H) for ArH group, 5.7 (s, 1H, OH) group.

The FTIR spectrum of (CoP3) which indicated absorption bands t (3200 cm -1 ) to (aromatic -CH stretching), (2923 cm -1 ) to (aliphatic -CH stretching), absorption bands around (1610-1549 cm -1 ) show the presence of the aromatic ring, the sharp band at (1619 cm -1 ) to (C=O amide), (1537 cm -1 ) to vinyl segment and (748 cm -1 ) to (C-Br).

The FTIR spectrum of (CoP4) which indicated absorption band at (3210 cm -1 ) to (aromatic-CH stretching), absorption ands around (1654-1633 cm -1 ) show the presence of the aromatic ring, (1570-1511 cm -1 ) to heteroaromatic ring (C=N) and the sharp band at (1588 cm -1 ) to (C=O amide).

1 H NMR spectrum of (CoP4), assigns the following chemical shifts; δ (2.5) ppm for DMSO, δ (6.1) ppm (s,1H ) for N-H group, δ (6.7 -8.5) ppm for Ar-H group.

The FTIR spectrum of (CoP5) which indicated absorption bands at (3213 cm -1 ) to (aromatic -CH stretching), (2943 cm -1 ) to (aliphatic -CH stretching), absorption bands around (1608-1538 cm -1 ) show the presence of the aromatic ring, the sharp band at (1630 cm -1 ) to (C=O amide) and (818 cm -1 ) to (C-Cl).

The FTIR spectrum of (CoP6) which indicated absorption band at (3315 cm -1 ) to (-OH group), (3207 cm -1 ) to (aromatic -CH stretching), absorption bands around (1645-1627 cm -1 ) show the presence of the aromatic ring, (1547-1498 cm -1 ) to heteroaromatic ring (C=N), the and at (1634 cm -1 ) to (C=O amide) and (687 cm -1 ) to (C-Br).

Differential scanning calorimetry study: From the DSC curves, the glass transition temperature (Tg), the crystallization temperature (Tc) and the melting temperature (Tm) were measured.The endothermic peaks of copolyamides are related to melting temperature.This increased in Tm is assigned to the linear terephthalic acid and p-phennylenediacrylic acid moieties incorporated into the polymer back bone during synthesis of co-polyamide.Hence , Tm is higher fore CoP1, CoP2, CoP4 and CoP5 as the polymer chain more rigid par s and/or a polymer contains less free volume.Samples usually showed multiple endotherms which are explained as due to the fusion of different population of crystallites with different sizes.As expected , Tm values are lower for CoP3 and CoP6) due to the higher chain flexibility of the formers afforded with increasing the amount of methylene f polymeric back bone and steric hindrance of terminal functional groups can influence Tm of resultant polymers.In addition, the polymer CoP6, has the lowest thermal stability than the other polymers containing rigid pyridine and phenylene moieties.This behaviour can be explained by the presence of methylene units which are more vulnerable to thermo-oxidative processes [21][22][23] .

Glass transition temperature (Tg) of all co-polyamides wer in the range (236-254 °C), in case of copolyamides (CoP1, CoP2, CoP3, CoP4, CoP5 and CoP6) it is interesting to note that the change of the diacids had a noticeable Tg difference.In addition, endothermic peaks above their glass transition temperatures were observed in DSC scans, which may be attributed to the crystalline molecular structure for all co-polamides.The higher in Tg of (CoP1, CoP2, CoP4 and CoP5) compared to that analogous co-polyamides might be endorsed to the existence of hetroaromatic pyridine rings and phenylene moieties.This increased in Tg is assigned to the linear terephthalic and pphennylenediacrylic acids moieties incorp rated into the polymer back bone during synthesis of co-polyamide.Particularly, the end group contribution becomes significant 24 .Thus it will be interesting to introduce different chain ends using substitution reaction since end group modification in (CoP1, CoP2, CoP3 and CoP5) had a strong effect on Tg as observed in previous studies [24][25][26] .Usually, amore polar functional group causes Tg to be higher.Tg of co-polyamides may be strongly dependent on the inter-association of functional groups with the neighboring molecule as well as the volume fraction occupied by terminal groups 26 .It seems that several factors such as the rigidity, polarity, length and steric hindrance of terminal functional groups can influence Tg of resultant polymers.DSC data indicated that the CoP3 containing symmetric dimethyl substituted resulted in lower Tg value than that of unsubstituted co-polyamides.The consideration of segmental symmetry is useful in explaining this behavior.The dimethyl substitution leads to an symmetric segment which can result in less efficient chain packing and hence more free volume that led to relatively easier chain mobility of polymer segments in comparison with asymmetrical substituted and unsubstituted Co-polyamides, ultimatel leading to decrease in glass transition temperature.The Tg, Tm and Tc obtained from DSC are reported in Table-3.Solubility of Co-polyamides: Solubility of Co-polyamides CoP 1 -CoP 6 was qualitatively tested in organic solvents and the results are summarized in (Table-4).The method that attempt to enhance their processabilities and solubilities were either by introducing bulky groups, flexible linkages, or molecular asymmetry into the polymer backbones.In this work, the attachment of bulky pendant groups in polymer backbone not only could provide an enhanced solubility because of decreased packing density and crystallinity, but also could impart an increase in T g by restricting the segmental mobility 27 .

One of the major objectives of this work was producing Co-polyamides with improved solubility.The solubility was investigated as 0.02 g of polymeric sample in 5 mL of solvent.All of the newly synthesized Co-polyamides have good soluble in common polar and dipolar aprotic solvents without need for heating.


Conclusion

Six new aromatic Co-polyamides have been synthesized.For this purpose, a typical polycondensation process has been followed under mild conditions.The reaction variables, such as temperature, time, monomer concentration, solvent system etc. have been found to have strong influence on the molecular weight of the polymers.Synthesis of Co-polyamides containing methylene unit, Schiff-base linkages and pyridine hetero cyclic ring with adipic acid, phthalic acid, terephthalic acid and 4-phenylenediacrylic acid, respectively at 120 °C for 2 h under the nitrogen atmosphere.The polymers were characterized by proton nuclear magnetic resonance spectroscopy and infrared spectroscopy confirmed the molecular composition of six strictly alternating, highly ordered Co-polyamides having methylene chains as flexible spacers and phenylene or pyridine hetryclic groups as the rigid segments.From the DSC curves, the glass transition temperature, the crystallization temperature and the melting temperature were measured.All the polymers showed a glass transition temperature, in the range of 236-256 °C.The higher in Tg of ( CoP1, CoP2, CoP4 and CoP5) compared to that analogous Co-polyamides might be endorsed to the existence of hetroaromatic pyridine rings and phenylene moieties.This increased in Tg is assigned to the linear terephthalic and p-phennylenediacrylic acids moieties incorporated into the polymer back bone during synthesis of Co-polyamide.In the same time, the presence of symmetric dimethyl substituted together with ether linkages brings much more flexibility to the macromolecular chain and decreases the glass transition of the polymers CoP3 and CoP6.The melting temperatures of the CoP3 and CoP6 decrease with increasing the amount of methylene of polymeric backbone and steric hindrance of terminal functional groups.The CoP6 has the lowest melting point among the series of the result and Co-polyamides .Tm is higher fore CoP1, CoP2, CoP4 and CoP5 as the polyme