Sizing and Thermal Stability of Prepared Tetraaminophthalocyaninatocopper ( II ) Derivatives-grafted Polymers

Different polymers were prepared by condensation polymerization of sebacic anhydride and adipic anhydride with ethylene glycol and poly(ethylene glycol). Their number average molecular weights were determined by end group analysis. Then, they were grafted on the prepared phthalocyaninatocopper(II) compounds with the general formula (NH2)4PcCu(II) having amino groups of 3,3',3'',3'''or 4,4',4'',4'''positions. All prepared polymers, compounds, and phthalocyaninatocopper(II)-grafted polymers were characterized by FTIR. The sizing measurements were carried out in 3,3',3'',3'''(NH2)4PcCu(II) and 4,4',4'',4'''(NH2)4PcCu(II) compounds with and without grafting polymers. The results showed that the grafting process led to decreasing in particle size and increasing in surface area. The grafting process was reflected positively on the thermal degradation of 3,3',3'',3'''(NH2)4PcCu(II) and 4,4',4'',4'''(NH2)4PcCu(II) grafted polymers. They had higher thermal stability accompanied with higher char residue and T50% weight loss with 3,3',3'',3'''-(NH2)4PcCu(II) and their grafted polymers being the best.


Introduction
Phthalocyanines are solid materials that also known as azaporphyrin derivatives. The phthalocyanines are planar aromatic macro cycles and consisting of four isoindole subunits presenting an 18electron aromatic cloud delocalized over an arrangement of alternating carbon and nitrogen atoms [1].
Phthalocyanine-containing polymers can be considered as robust and processable materials in which the relative orientation of the constituent phthalocyanine units can be controlled by strong covalent bonding [2][3][4]. For this reason, the integration of phthalocyanines into macromolecules is a powerful tool to obtain new materials with outstanding properties [5,6].
There are mainly two routes to graft polymers into phthalocyanine, one of them involves the polymerization or (copolymerization) reaction of unsymmetrical substituted phthalocyanine, i.e. holding reactive sites on one isoindole subunits. This involves at least two steps, or even more, reaction steps which must be carried out in heterogeneous phase reaction. Also, it has been reported in the literature the synthesis and characterization of polymeric phthalocyanines obtained through the olefin metathesis polymerization of terminal olefin groups in the side chains of unsymmetrical phthalocyanine monomers [7]. The second one requires the preparation of a polymer (or copolymer) with active side functional groups that can react in a further step with an appropriately functioned phthalocyanine [1]. Both routes should be performed in suspension of solid phthalocyanine in a suitable solvent. In both cases the aim is to create chemical bonding between grafted polymer and 3,3',3'',3'''-or 4,4',4'',4'''traaminophthalocyaninatocopper(II) compounds. The second route is chosen for this work because of its simplicity.
Phthalocyanines have a thermal stability with no degradation up to (400-500) ºC, and most complexes do not decompose below 900ºC under vacuum [8].
The thermal stability of phthalocyanines showed attractive properties such as chemical inertness, semiconductivity, catalytic activity and photoconductivity [9]. These desirable properties prompte many investigators to incorporate the phthalocyanine structure in the synthesis of thermally stable polymers [10], and this is the main target of the current work.

Apparatus
Infrared spectra were recorded on Shimadzu FTIR-8400S double beam spectrophotometer. The particle size measurements were carried out in the range of 0.02 μm to 2000 μm using Laser Diffraction Particle Sizing technique built in Master sizing-2000. The thermal analysis of the compounds was carried out using a (TGA Q50-USA) with the range (20-700) °C at a constant heating rate of 10 °C min -1 under continuous nitrogen flow.

Preparation of 3-and 4-nitro phthalic anhydride
In a 100m1 round-bottom flask fitted with a reflux condenser, 21g (0.1mol) of 3-nitrophthalic acid and 20g (18.5ml, 0.2mol) access of acetic anhydride were placed. The mixture was heated to boiling until a clear solution was obtained, and heating was extended for another 10 minutes. The hot mixture was poured into a large porcelain dish and was allowed to cool. It was washed twice with 15m1 absolute ethanol followed by filtration and dried in air for a short time [11]. The yield of 3nitrophthalic anhydride), was 17g (88%), mp 163-165 °C (Lit. mp 163-164°C). The same procedure was applied to the synthesis of 4nitrophthalic anhydride using about 21g (0.1mole) of 4-nitro phthalic acid and acetic anhydride 20g (18.5ml, 0.2mol), and the yield 17g (88%), mp 116-120°C. Preparation of 3, 3', 3'', 3'''tetranitrophthalocyaninatocopper(II) [12] Hydrated cupric sulphate, CuSO 4 .5H 2 O, (2 g, 8mmol), 3-nitro phthalic anhydride (4.73g, 32mmol), ammonium molybdatetetrahydrate (0.2g 0.18mmol), ammonium chloride (0.5g, 9mmol) and excess of urea (30g, 0.5mol) were grounded and placed in 250 ml round bottom flask containing 100ml of nitrobenzene, Scheme 1. The temperature of the stirred reaction mixture was raised gradually to 185°C and kept at this temperature for 5hrs. The hot mixture was filtered and the solid product was washed with ethanol repeatedly to remove the excess of nitrobenzene. The solid product was dried and added to 200ml of 1N HCl and then refluxed for 1hr, cooled to room temperature to give solid product that was filtered. The solid product was poured into 200 ml of 1N NaOH and refluxed for 1hr, filtered and washed with distilled water. The blue powder was obtained with 82% yield. The complex 4,4`,4``,4```tetranitrophthalocyaninatocopper(II) was synthesized with 84% yield in the same procedure using the prepared 4nitrophthalic anhydride. (4g, 0.0053mol) and 10g (0.041mol) of Na 2 S.9H 2 O (excess) in 50 ml of water was heated at 60 ºC with stirring for 12hrs. The reaction mixture was cooled and filtered. The solid product was refluxed with 50ml of aqueous solutions 0.5N of NaOH for 1hr follow by of aqueous solutions 0.5N of HCl for 1hr. The mixture was filtered and washed with hot water and dried at 110 ºC. The yields were about 69-70% .
Ethylene glycol monomer (6.2g, 0.1mol) was dissolved in dry toluene (80ml), and the solvent was distilled off to a final volume of 30 ml to remove the residual water adsorbed to the polymer. Adipoyl chloride (20.13g, 0.11mol) or sebacoyl chloride and triethyl amine (20.2ml, 0.2mole) were added to the reaction mixture, and stirred at 25 ºC for 18hrs. The products were isolated by precipitation from diethyl ether, and then dissolved in methylene chloride and fractionally precipitated by slowly adding to diethyl ether. The products were white solid followed the filtration and drying processes with 90-91% yield [13,14]. They were characterized by infrared spectroscopy, and their molecular weights were determined by carboxyl-end group analysis and the results obtained are shown in Table 1.

Preparation of poly(ethylene glycol)sebacic acid polyester
Poly(ethylene glycol)-sebacic acid polyester was prepared following the same procedure mentioned above using 0.2629g (0.0011mol) of sebacoyl chloride with 6g (0.001mol) of poly(ethylene glycol) having molecular weight 6000 or 10g (0.001mol) of poly(ethylene glycol) having 10000 molecular weight and 20g (0.001 mol) of poly(ethylene glycol) having 20000 molecular weight to give a white solid product with yield 75%,72% and 70% respectively. It was also characterized by infrared spectroscopy. Number average molecular weights of all the prepared polymers were determined by carboxyl-end group analysis method. The obtained results are also listed in Table 1. Grafting process of phthalocyanines with different prepared polymers A phthalocyanine derivative 0.5g was added to a certain polymer solution prepared by dissolving 1g in 20 ml ethanol. The mixture was transferred to a one-neck round bottom flask, then it was refluxed for 3hrs and left to cool down to ambient temperature. The solid was filtered and washed three times with ethanol. The solid product was dried at room temperature. It was characterized by infrared spectroscopy [15]. Table 2 exhibits the yield of the grafting process of phthalocyanine derivatives with different polymers.

Results and discussion
Characterization of phthalocyanine compounds by FTIR All prepared compounds, polymer and the grafted products were characterized by IR-spectroscopy in the form of KBr discs. The IR spectra of 3,3',3'',3'''-(NO 2 ) 4 PcCu(II) and 4,4',4'',4'''-(NO 2 ) 4 PcCu(II) are shown in Figure 1 and Figure 2 respectively. They revealed that a presence of a band at 1537cm -1 assigned for N-O bond asymmetric stretching, while the symmetric stretching appears at 1342 cm -1 , literature range (1340-1330) cm -1 [16]. This is beside the presence of other bands assigned to the Pc's chemical structure, for example, C=N bond and C=C bond, and the stretching band for C-N bond appears at 1249 cm -1 [17,18].

FTIR characterization of prepared polymers
The spectra of polymers were demonstrating broadening under the O-H stretching vibration between 3700 and 2400 cm -1 , characteristic of the hydrogen bonded -OH groups of the carboxyl end groups and associated with stretching vibration bands of carbonyl groups of polymers at (1700-1690) cm -1 [18], Figure 5 is a representative figure of the infrared spectra of the all prepared polymers. In addition, the presence of ester group gave a strong peak at (1735-1730) cm -1 for stretching carbonyl-ester group as well as two peaks at (1250-1215) cm -1 and (1180-1170) cm -1 assigned for C-O bond of ester groups. Other peaks at 2933 cm -1 and 2856 cm -1 represent symmetric and asymmetric stretching of the aliphatic C-H bond of methylene groups respectively [19,20]. Table 3 shows the important bands and their functional group assignments.

FTIR characterization of phthalocyaninatocopper(II) grafted polymers
It has been reported [21] that the strength of the solid-grafted polymer interaction can be enhanced by introducing a polymer having a functional group, such as carboxyl group, which is able to bind to solid through a covalent bond, and this is the case here. All the polymers prepared have carboxyl end-groups are able to react with amino groups of 3,3',3'',3'''-(NH 2 ) 4 PcCu(II) and 4,4',4'',4'''-(NH 2 ) 4 PcCu(II) to form new amide functional groups. This may reflect positively on the properties of Pc derivatives that can be used for various applications. Figure 6 shows the IR spectrum of 3,3',3'',3'''-tetraaminophthalocyaninato copper(II)-grafted PEA. As expected, it shows the disappearance of hydrogen bonded hydroxyl groups and appearance of a new characteristic N-H stretching band of the amide group at 3330 cm -1 , and for 4,4',4'',4'''tetraaminophthalocyaninato copper(II)grafted PEA at 3350 cm -1 , Figure 7, literature range (3330-3060) cm -1 , while the N-H bends vibration at 1580 cm -1 and at 1570 cm -1 respectively, the literature range (1570-1515) cm -1 [19]. The carbonyl amide group appears as shoulder at 1690 cm -1 with a sharp stretching band of the ester carbonyl group at 1740 cm -1 due to the higher concentration of the latter group for 3,3',3'',3'''-tetraaminophthalocyaninato copper-grafted PEA and at 1728 cm -1 for 4,4',4'',4'''-tetraaminophthalocyaninato copper-grafted PEA, literature range (1735-1730) cm -1 [19]. Also, the grafting process is confirmed by the appearance of new stretching bands assigned for aliphatic methylene C-H at  Thermal gravimetric analysis (TGA) is one of the methods of thermal analysis techniques used to study the thermal stability of a wide variety of materials. The results obtained from thermal gravimetric of the Pc derivatives and their grafted polymers are listed in Table 5.
The data in the Table 5  This may be attributed to the fact that 3-substituted precursor can dictate predominant forms of the least structurally crowded and least soluble phthalocyanine [22]. The other reason may be due to steric hindrance raised from the formation of the hydrogen bonding between hydrogen atom of the amino groups of 3Pc and the nitrogen of Aza Bridge to form hexagonal rings [23]. In contrast, this suggested structure was never formed in 4,4',4'',4'''-(NH2)4PcCu(II), because their amino groups were far away compared to their positions in 3,3',3'',3'''-(NH2)4PcCu(II) and the hydrogen bonding was never formed. Therefore, one can conclude that the hydrogen bonding formed in 3,3',3'',3'''-(NH2)4PcCu(II) increases thermal stability. It is also clearly shown that phthalocyanine (in 3,3',3'',3'''-and 4,4',4'',4'''-substituted positions) before grafting have only one decomposition temperature for each one, while after the polymer grafting process, their thermo grams exhibit more than one at most. The two decompositions confirm that grafting polymers on Pc molecules increase the degree of degradation and the range of thermal decomposition and enhance their thermal stability and in turn may increase the area of their applications.

Sizing measurements
Particle size distribution is the statistical relation between amount and size of a given solid powder, also it exhibits the statistical relation between amount (normalized particle amount), and the size (particle diameter). All Figures demonstrate different attitude in particle size distribution shape in comparison to polymer grafted phthalocyanine derivatives. Figures 10  and 11 show the particle size distribution of ungrafted 3,3',3'',3'''-(NH 2 ) 4 PcCu(II) and 4,4',4'',4'''-(NH 2 ) 4 PcCu(II) respectively and Figures  12 and 13 for grafted phthalocyanine derivatives. These changes in shape imply that real grafting were obtained, and can be considered as another proof for the grafting process beside the infrared spectra.
The calculated results obtained are listed in Table 6. Examining Table 6, one can observe that the specific surface area increases for the polymer grafted phthalocyanine in both 3,3',3'',3'''-(NH 2 ) 4 PcCu(II) and 4,4',4'',4'''-(NH 2 ) 4 PcCu(II). In comparison with ungrafted compounds, this indicates that the grafting process increases the surface area of solid particles, while other parameters (particle size, surface weight mean, volume weight mean and [d (0.1), d (0.5) and d (0.9)] decrease compared with 3Pc and 4Pc before grafting.   The aggregation tendency of phthalocyanines is depicted as a coplanar association of rings progressing from monomer to dimmer and higher order complexes and it is dependent on concentration, nature of solvent and kind of substituts, type of metal ions and temperature [24].
One of the obtained results about the complexes whose bulky group substituted at the peripheral positions was a decreasing of the aggregation [25]. Therefore, particle size and other parameters decreased after grafting which may be attributed to polymer chain that decrease the ability of phthalocyanine molecular for aggregation by the bulky effect of these chains and at the same time increases the specific surface area. Therefore, this indicates the occurrence of grafting process. On the other hand, larger molecular weight of all the polymers which are grafted with phthalocyanine prevented particle growth through steric hindrances. The presence of functional groups on polymer chains that's grafted with Pc may ensure nanoparticle's surface stabilization through electrostatic repulsive forces leading to prevent particles to grow [26].