Thermoanalytical Study and Kinetics of New 8-Hydroxyquinoline 5-sulphonic Acid-Oxamide-Formaldehyde Terpolymer Resins

The terpolymer resins (8-HQ5-SAOF) have been synthesized by the condensation of 8-hydroxyquinoline 5-sulphonic acid (8-HQ5-SA) and oxamide (O) with formaldehyde (F) in the presence of acid catalyst and using varied molar proportion of the reacting monomers. The synthesized terpolymer resins have been characterized by different physico-chemical techniques. Thermogravimetric analysis of all terpolymer resins in present study have been carried out by non-isothermal thermogravimetric analysis technique in which sample is subjected to condition of continuous increase in temperature at linear rate. Thermal study of the resins was carried out to determine their mode of decomposition and relative thermal stabilities. Thermal decomposition curves were studied carefully with minute details. The Freeman-Carroll and Sharp-Wentworth methods have been used in the present investigation to calculate thermal activation energy and different kinetic parameter of the terpolymer resins. Thermal activation energy (Ea) calculated with above two mentioned methods are in close agreement. The advantage of Freeman-Carroll method is to calculate both the order of reaction (n) and energy of activation in one single stage by keeping heating rate constant. By using data of thermogravimetric analysis, various thermodynamic parameters like frequency factor (Z), entropy change (∆S), free energy change (∆F) and apparent entropy (S*) have been determined using Freeman-Carroll method.


Introduction
The synthesized terpolymer resins, showing versatile applications and properties, attracted the attention of scientist and introduce the recent innovations in the polymer chemistry.
These terpolymers can be used as high energy material 1 , ion-exchanger 2 , semiconductors 3 , antioxidants, fire proofing agent, optical storage data, binders, molding materials etc. Literature survey reveals the chelating ion-exchange properties of 2, 4-dinitrophenylhydrazone of 2-hydroxyacetophenone-formaldehyde resin 4 , and oximes of 2-hydroxyacetophenone-substituted benzoic acid-formaldehyde resin 5 for different metal ions.Thermogravimetric analysis of ureaformaldehyde polycondensate (UFPS) has been reported by Zeman and Tokarova 6 .Terpolymer resins having good thermal stability have enhanced the scope for development of some polymeric materials.The study of the thermal degradation of terpolymer resins have recently become a subject of interest.Zhao Hong et al. studied the thermal decomposition behaviour of phosphorous containing copolystar 7 .In an earlier communication [8][9][10][11] from this department numbers of studies on such terpolymers have been reported.However no work seems to have been carried out on thermo analytical and kinetic studies of the terpolymer resins from 8-hydroxyquinoline 5sulphonic acid-oxamide and formaldehyde.The present paper explores the thermal analysis giving their relative thermal stabilities by applying the Sharp-Wentworth and Freeman-Carroll methods.Energy of activation (Ea), Kinetic parameter viz.Z, ∆S, ∆F, S*, and order of reaction (n) were determined by applying Freeman-Carroll Method.

Experimental
The entire chemical used in the synthesis of various new terpolymer resins were procured from the market and were Analar or Fulka or chemically pure grade.Whenever required they were further purified by standard methods.

Synthesis of 8-HQ5-SAOF terpolymer resins
The new terpolymer resin 8-HQ5-SAOF-1 was synthesized by condensing 8-hydroxyquinoline 5-sulphonic acid (2.43 g, 0.1 mol) and oxamide (0.88 g, 0.1 mol) with 37% formaldehyde (7.4 mL, 0.2 mol) in a mol ratio of 1:1:2 in the presence of 2 M 200 mL HCl as a catalyst at 130 0 C ± 2 0 C for 6 h in an oil bath with occasional shaking to ensure thorough mixing.The separated terpolymer was washed with hot water and methanol to remove unreacted starting materials and acid monomers.The properly washed resin was dried, powdered and then extracted with diethyl ether and then with petroleum ether to remove 8-hydroxyquinoline 5-sulphonic acid formaldehyde copolymer which might be present along with 8-HQ5-SAOF terpolymer.The yellow color resinous product was immediately removed from the flask as soon as reaction period was over and then purified.The reaction and suggested structure of 8-HQ5-SAOF-1 in shown in Figure 1.The terpolymer was purified by dissolving in 10% aqueous sodium hydroxide solution, filtered and reprecipitated by gradual drop wise addition of ice cold 1:1 (v/v) concentrated hydrochloric acid / distilled water with constant and rapid stirring to avoid lump formation.The process of reprecipitation was repeated twice.The terpolymer sample 8-HQ5-SAOF-1 thus obtained was filtered, washed several times with hot water, dried in air, powdered and kept in vacuum desicator over silica gel.The yield of the terpolymer resin was found to be 80%.

Characterization of terpolymer resins
The viscosities were determined using Taun-Fuoss viscometer at six different concentrations ranging from 1.00 to 0.031% of terpolymer in DMSO at 30 °C. the intrinsic viscosity η was calculated by relevant plots of the Huggins' equation and Kraemmer's equation.
The number average molecular weights were determined by conductometric titration in non aqueous medium such as dimethylsulphoxide (DMSO) using ethanolic KOH as a titrant.From the graphs of specific conductance against milliequivalents of base, first and last break were noted from which degree of polymerization Electron absorption spectra of all terpolymer resins were recorded in DMSO (spectroscopic grade) on Shimadzu double beam spectrophotometer in the range of 200 to 850 nm at Sophisticated Analytical Instrumentation Facility, Punjab University, Chandigarh.Infra-red spectra of four 8-HQ5-SAOF terpolymer resins were recorded on Perkin-Elmer-983 spectrophotometer in KBr pallets in the wave number region of 4000-400 cm -1 at SAIF, Punjab University, Chandigarh.Nuclear Magnetic Resonance (NMR) spectra of newly synthesized terpolymer resins have been scanned on Bruker Advanced 400 NMR spectrometer using DMSO-d 6 at sophisticated Analytical Instrumentation Facility Punjab University, Chandigarh.TGA of all terpolymer resins have been carried out by using Perkin-Elmer TGS-II Thermogravimetric Analyzer at heating rate of 10 ºC per minute up to 800 ºC at SICART, Vallabhvidya nagar, Gujarat.

Results and Discussion
All the newly synthesized purified 8-HQ5-SAOF terpolymer resins were found to be yellow in colour.The terpolymers are soluble in solvents such as DMF, DMSO and THF while insoluble in almost all other organic solvents.The melting points of these terpolymers were determined by using electrically heated melting point apparatus and are found to be in the range of 436 to 449 K.These resins were analyzed for carbon, hydrogen, nitrogen and sulpher content.The details of elemental analysis are incorporated in Table 1.The terpolymer which has been used in the present investigation was prepared by the reaction given in Figure 1.The number average molecular weight ) n M ( of these terpolymers has been determined by conductometric titration method in non-aqueous medium and using standard potassium hydroxide (0.05 M) in absolute ethanol as a titrant.The results are presented in Table 1.The specific conductance was plotted against milliequivaletns of ethanolic KOH required for neutralization of 100 g of each terpolymer.There are several breaks before the complete neutralization of all phenolic hydroxyl groups.The first break in the plot was the smallest break and assumed that this corresponds to a stage in titration when an average one phenolic hydroxyl group of each chain was neutralised.
From the plot, the first and last breaks were noted.The average degree of polymerization It is observed that the molecular weight of terpolymers increases with increase in 8-hydroxyquinoline 5-sulphonic acid content.This observation is in agreement with the trend observed by earlier workers 12,13 .
Viscosity measurements were carried out at 300 K in freshly triple distilled dimethylsulphoxide (DMSO) using Tuan-Fuoss Viscomer, at six different concentrations ranging from 1.00% to 0.031%.Reduced viscosity versus concentration was plotted for each set of data.The intrinsic viscosity [η] was determined by the corresponding linear plots.Huggins' and Kraemmer's constants were determined by an expression 1 and 2.
According to the above relations, the plots of η sp /C and lnη rel /C against C were linear with slopes of K 1 and K 2 respectively.By extrapolating linear plot to zero concentration, intercepts on the viscosity function axis give [η] value in both plots.The values of intrinsic viscosity obtained from both plots have been found to be closed agreement with each other.The calculated values of the constants K 1 and K 2 in most cases satisfy the relation K 1 + K 2 = 0.5 favourably 14 .It was observed that terpolymer having higher Mn shows higher value of [η] which are in good agreement with earlier co-workers 14,15 .
The UV-Visible spectra of all the 8-HQ5-SAOF terpolymer samples in pure DMSO were recorded in the region 200-850 nm at a scanning rate of 100 nm min -1 and a chart speed of 5 cm min  transition indicates the presence of -NH and -OH group.The hyperchromic effect is due to the presence of -OH and -NH groups, which act as auxochrome 16 .From the spectra of 8-HQ5-SAOF terpolymer resins it is observed that ε max value gradually increases in the order of 8-HQ5-SAOF-1< 8-HQ5-SAOF-2 < 8-HQ5-SAOF-3 < 8-HQ5-SAOF-4.The increasing order of ε max values may be due to introduction of more and more aromatic ring and auxochrome phenolic -OH and -NH groups in the repeated unit of the terpolymer resins.The observation is in good agreement with proposed structures of above terpolymer resins.
The IR spectral studies revealed that all these terpolymers gave rise to nearly similar pattern of spectra.A broad absorption band appeared in the region 3500-3510 cm -1 may be assigned to the stretching vibrations of phenolic hydroxyl (-OH) groups exhibiting intramolecular hydrogen bonding 17 .A sharp strong peak at 1500-1650 cm -1 may be ascribed to aromatic skeletal ring.The bands obtained at 1150-1250 cm -1 suggest the presence of methylene (-CH 2 ) bridge 18 .The 1,2,3,5 substitution of aromatic benzene ring recognized by the sharp, medium / weak absorption bands appeared at 960-980, 1120-1055, 1210-1182 and 1320-1280 cm -1 respectively.The presence of sharp and strong band at 3390-3410 cm -1 indicates the presence of -NH bridge.This band seems to be merged with very broad band of phenolic hydroxyl group.
The NMR spectra of all four 8-HQ5-SAOF terpolymers were scanned in DMSO-d 6 solvent.From the spectra it is revealed that all 8-HQ5-SAOF terpolymers gave rise to different pattern of The polymers under study are terpolymer and hence, it is very difficult to assign their exact structures.However, on the basis of the nature and reactive site of the monomers and taking into consideration the linear structure of other substituted phenol-formaldehyde polymers and the linear branched nature of urea-formaldehyde polymers the most probable structures of proposed for 8-HQ5-SAOF terpolymers have been shown in Figure 2. Thermogram of all 8-HQ5-SAOF terpolymer resins have been recorded using Perkin-Elmer thermogravimetric analyzer.Brief accounts of thermal behaviour of these terpolymers are given.But for reason of economy of space the thermal data and kinetic plots for only one representative case have been given in Figure 3-6.

TG of 8-HQ5-SAOF-1 terpolymer
Thermogram of the terpolymer is shown in Figure 3 and depicts three steps decomposition in temperature range 40-800 0 C, after loss of water molecule (5.04% found and 5.06% calculated).First step decomposition starts from 120-290 0 C which represents the degradation of side chain attached to aromatic nucleus and hydroxyl group (32.13% found and 32.58% calculated).Second step decomposition starts from 290-460 0 C, corresponding to 69.26% loss of aromatic nucleus against calculated 69.38%.Third step decomposition starts from 460 to 800 0 C which corresponds to loss of oxamide moiety with its side chains (99.85% found and 100.00% calculated).Consequently no residue may be assigned after complete degradation.
In the present investigation Sharp-Wentworth and Freeman-Carroll methods have been used to determine the kinetic parameters of 8-HQ5-SAOF terpolymer sample.Sharp-Wentworth method: In this method following expression is used.
Where β is the linear heating rate.The graph of ( )  A plot of percentage mass loss versus temperature is shown in Figure 3 for representative 8-HQ5-SAOF-1 terpolymer.From the TG curves, the thermo analytical and the decomposition temperature were determined Table 2 to obtain the relative thermal stabilities of the various polymers.The method described by Sharp -Wentworth was adopted.Based on the initial decomposition temperature, the thermal stabilities of the terpolymers, have also been used here to define their relative thermal stabilities, neglecting the degree of decomposition Table 2.  Using thermal decomposition data and then applying the Sharp-Wentworth method (A representative Sharp-Wentworth plot of 8-HQ5-SAOF-1 terpolymer is shown in Figure 4) activation energy is calculated which is in agreement with the activation energy calculated by Freeman-Carroll method 22 .A representative thermal activation energy plot of Sharp-Wentworth method Figure 4 and Freeman-Carroll method (Figure 5 & 6) for the polymer have been shown.Thermodynamic parameters such as entropy change (∆S), free energy change (∆F), frequency factor (Z) and Apparent entropy (S*) calculated on the basis of thermal activation energy are given in Table 2, using equations are given below.By using the data of the Freeman-Carroll method, various thermodynamics parameters have been calculated Table 2.The values of these thermodynamic parameters for all terpolymers are about the same.The similarity of the values indicates a common reaction mode, 20 from the abnormally low values of frequency factor, it may be concluded that the decomposition reaction of 8-HQ5-SAOF terpolymers can be classed as a 'slow' reaction.There is no other obvious reason 23,24 .

( ) ( )
Fairly good straight line plots are obtained using the two methods.This is expected since the decomposition of terpolymer is known not to obey first order kinetics perfectly 23,24 .

2.
In TGA the energy of activation evaluated from the Sharp-Wentworth and Freeman-Carroll methods are found to be nearly equal and the kinetic parameters obtained from Freeman-Carroll method are found to similar, indicating the common reaction mode.However, it is difficult to draw any unique conclusion regarding the decomposition mechanism.

3.
Low values of frequency factor may be concluded that the decomposition reaction of 8-hydroxyquinoline 5-sulphonic acid-oxamide-formaldehyde terpolymer can be classified as 'slow reaction'.4.
Thermogravimetric study concluded that these terpolymers are thermally stable at elevated temperature.
for each terpolymer resin.

X
have been determined using the formula.Total milliequivaletns of base required for complete neutralisation ) DP ( = Milliequivalents of base required for smallest interval Repeat unit weight

- 1 .
All the four 8-HQ5-SAOF terpolymer samples gave two characteristics bands at 310-330 nm and 230-275 nm.These observed positions for the absorption bands have different intensities.The more intense band is due to *

1 H
NMR spectra, since each of 8-HQ5-SAOF terpolymer possesses set of proton having different electronics environment.The chemical shift (δ) ppm observed is assigned on the basis of data available in literature19 .The singlet obtained in the region 5.12-4.92(δ) ppm may be due to the methylene proton of Ar-CH 2 -N moiety.The signals in the region 7.30-7.39(δ)ppm are attributed to protons of -NH bridge.The weak multiplate signals (unsymmetrical pattern) in the region of 8.21-8.18(δ)ppm may be attributed to aromatic proton (Ar-H).The signals in the range at 9.08 to 9.02(δ) ppm may be due to phenolic hydroxyl protons.The much downfield chemical shift for phenolic -OH indicates clearly the intramolecular hydrogen bonding of -OH group20,21 .The signals in the range of 10.02-10.08(δ)ppm are attributed to proton of -SO 3 H groups.
T has been plotted.The graph is a straight line with Ea as slope and A as intercept.The linear relationship confirms that the assumed order (n) = 1 is correct.Freeman-Carroll method: In this method following expression is used.
∆logWhere, dw/dt = rate of change of weight of terpolymer sample with respect to time Wr = Wc-W, where Wc is the weight loss at the completion of the terpolymer reaction or at definite time and W is the total weight loss up to time t.T is the temperature, R is the gas constant and n is the order of reaction.Hence the graph of Should give on Y axis (x=0) an intercept for the value of n, the order of reaction and the slope m = -Ea/2.303R.The detailed procedure is clearly laid out for one representative sample as an illustration.