Indian Journal of ChemistryVol. 22A, February 1983, pp. 117-119

Synthesis & Characterization of Terpolymers of SalicylicAcid & Thiourea with Trioxane

M M PATEL* & R MANAVALAN

Department of Chemistry, Sardar Patel University, Vallabh Vidyanagar 388 120

Received 18 September 1982; revised and accepted 3 November 1982

The terpolymers have been synthesised by the condensation of salicylic acid (S) and thiourea (T) with trioxane(T) in tbe presence of acid catalysts at varying molar proportions of tbe reactants. Terpolymer prepared fromequimolar proportions of the reactants in the presence of 2M HCl has been fractionated by fractional precipitationmethod. Compositions of the terpolymers have been arrived at by elemental analyses and non-aqueous conducto-metric titration. IR spectra have also been recorded in order to elucidate the structure of the terpolymers. Thenumber average molecular weight (Mn) of each terpolymer has been estimated by vapour pressure osmometry.Intrinsic viscosities of the solutions of all terpolymers have been determined in dimethylformamide. Thermalbehaviour of each terpolymer has also been studied by thermogravimetric analysis.

Salicylic acid-formaldehyde (SF) polymers havefound many applications'>". However, the terpoly-mers of salicylic acid and thiourea with trioxanehave not been studied so far. This motivated us toprepare such terpolymers and to study their proper-ties. Terpolymer formation did not occur in thepresence of basic catalyst like NaOH. Hence thesewere prepared in the presence of acidic catalysts like2M HCI, 2M H2S04 and glacial acetic acid. Thecharacterization of terpolymers is based on (i) ele-mental analyses, (ii) infrared data, (iii) TG analysis,(iv) conductometric titrations in non-aqueous medium'and (v) intrinsic viscosity measurements in DMF.

Materials and MethodsAll the reagents used were of either AR or chemi-

cally pure grade.(A) Condensation of salicylic acid (S) and thiourea

(T) with trioxane (T) in the presence of 2M HCl-Amixture of salicylic acid (0.1 mol), thiourea (0.1 mol)and trioxane (0.2 mol) in 2M HCI was heated in oil-bath at 130±2°C for 4 hr. The separated yellowcoloured polymer was washed with hot water andfinally with ether to remove excess of acid monomerand SF polymer. The polymer was purified bydissolving in 10% NaOH and reprecipitating bydropwise addition of 1 : 1 (v/v) HCI/water. Theprocess was repeated twice. The terpolymer sample,thus obtained, was washed with boiling water anddried.

Condensation of salicylic acid and thiourea withtrioxane in presence of 2M H2S04 (method-B) andcondensation in presence of glacial acetic acid(method-C) were carried out as described above.The characterization of SIT terpolymers thusobtained are given in Table 1.

Fractionation of STT-J terpolymer-The fractional

precipitation method was employed for fractionatingterpolymer sample STT-l (Table J). DMF was usedas the solvent and HCl/water mixture (1 : 1, v/v) asprecipitant. A 3% solution of terpolymer samplewas prepared (solvent DMF) and filtered throughG2 sintered glass funnel. The Don-solvent mixturewas added dropwise to the solution until the scatteredlight exhibited moderately strong opalescence, keep-ing the solution continuously stirred. The solutionwas warmed till the opalescence completely disappea-red. The solution was then allowed to cool to attainthermal equilibrium in the thermostat (30±O.1°C)with continuous stirring. The flask was left over-night in the thermostat whereby the precipitateagglomerated and settled down at the bottom of theflask. The supernatant liquid was syphoned off intoanother flask, the settled polymer in the form of filmwas scratched off and cI\-ied. Proceeding in thismanner, a series of fractions (SIT-la, SIT-lb,STT-Ic and STT-Id, Table 1) of regularlydecreasing molecular weights were collected.

Physical measurements-Nitrogen estimation inpolymer samples were carried out by Kjeldahlmethod. Sulphur was estimated as BaS04 by Cariusmethod. The conductivity of the polymers inpyridine was measured by the method reported forp-hydroxybenzoic acid-formaldehyde polymers"using a conductivity bridge fabricated by M/s.Konductoskop Metrohm Harisau, Switzerland.Number average molecular weight (Kin) of all theterpolymers was estimated by VPO method. DMFwas used as solvent and benzil as calibrant. Theviscometric measurements of solutions of terpolymersin DMF were carried out with an Ubbelohde typeviscometer at 35±0.1°C. IR spectra were recordedon UR-IO spectrophotometer in KBr. TGA wasperformed at a heating rate of lOoe min? in air.

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INDIAN J. CHEM., VOL. 22A FEBRUARY 1983

Table I-Per Cent Yield, Elemental Analyses, Molecular Weights and Intrinsic Viscosities of STT Terpolymers

No.' Mole ratio Method Yield Reqd (found) % Mole ratio of S : T (Mn)of monomers of % -------

S : T: T'" prepara- N S from ele- Conduct- Conductometry** VPO [7)] X 10"tion mental ometry ------- (dl g-l)

analysis Pyridine Sodiummethoxide

1 : 1 : 2 A 74.5 11.76 13.44 0.43 0.45 1098 1143 850 6.28(11.06) (12.81 ) 0.38 0.37

1a Fraction 12.5 11.76 13.44 0.45 0.47 1294 1249 900 10.35(10.30) (11.79) 0.37 0.33

1b -do- 10.0 11.76 13.44 0.44 0.41 1121 1191 825 6.7(10.90) (J 2.52) 0.39 0.43

1c -do- B.33 11.76 13.44 0.43 0.46 1013 1047 780 6.3(11.25) (12.88) 0.41 0.34

1d -do- 6.66 11.76 13.44 0.42 0.42 950 904 729 5.4(12.43) (14.21) 0.44 OAI

2 3 : 1 : 4 A 41.2 5.21 5.94 0.57 0.59 976 971 730 5.24(4.42) (5.06) 0.16 0.13

3 1 : 3 : 4 A 70.5 20.28 23.18 0.22 0.35 939 928 715 4.88(22.54) (24.35) 0.76 0.53

4 1 : 1 : 1 A 58.9 11.76 13.44 0.38 0.4 745 738 608 5.12(12.83) ( 12.82) 0.49 0.45

5 1 : 1 : 4 A 69.2 11.76 13.44 0.39 0.39 801 929 645 4.85(12.56) (14.29) 0.46 0.47

6 1 : 1 : 2 B 72.9 11.76 13.44 0.44 0.45 1049 1023 825 7.1(J 0.53) (12.05) 0.37 0.36

7 1 : 1 : 2 C 57.0 11.76 13.44 0.41 0.43 850 868 524 5.05(12.23) (13.99) 0.44 0040

8 3 : 1 : 3 C 37.9 5.21 5.94 0.54 0.51 B12 762 603 4.98(6.14) (6.49) 0.22 0.26

9 1: 3 : 4 C 58.7 20.28 23.18 0.19 0.28 791 834 504 5.25(21.69) (24.16) 0.81 0.71

"'S--salicylic acid, T-thiourea, T-trioxane"''''titrant

Results and DiscussionThe calculated and observed values of nitrogen

and sulphur (Table 1) are comparable in the case ofterpolymers prepared from equimolar proportions ofsalicylic acid and thiourea. But, the values areslightly different and less comparable for polymerswhich were prepared from non-equimolar proportionsof salicylic acid and thiourea. For these, nearlyconsistent results were objained, The differences inthe values of elemental nitrogen and sulphur estima-tion have been commonly observed in polymersample". Terpolymer samples were in the powderform having pale yellow colour. They were solublein both pyridine and DMF. Exact melting pointsof the samples could not be determined due tosoftening at 110aC The monomer contents of thepolymer samples were calculated from both con-ductometric titrations and sulphur estimation andthe values were found to be comparable. The degreeof polymerization (OP) and Mn were evaluated fromconductometric titrations using sodium methoxideand tetrabutyl-ammonium hydroxide (TBAH) astitrants. The Mn values were also evaluated by VPOmethod. There was a fair agreement between thetwo sets of values (Table 1). Slight differencesnoticed are due to certain inherent assumptions inthe conductometry method. Moreover conducto-metric titrations are not fully applicable for thedetermination of Mn of the terpolyrners". Time of

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flow of dimethyl formamide was found to be 160sees in the Ubbelohde viscometer.

It has been observed that those terpolymers andfractions having higher (Mn) values show higherintrinsic viscosity ['I]' It is also noted that ['I] ofpolymer samples (Table 1) obtained using greaterquantity of catalyst is usually higher in confirmationwith the observations of Burke and Coworkerst-",Kinetic energy and shear corrections were not takeninto consideration.

The IR spectra of all the terpolymer samples andfractions are found to be similar except for somedifferences in the intensities of a few peaks. Thelowering of vC=O of salicylic acid at 1665 cm-1 inthe terpolymers may be due to the nature of substitu-tion", The bands in the regions 2800-3300, 1400-1500,1200-1350 and 150-800 cm-1 suggest the presence ofmethylene bridges in the STT terpolymers'". Thespectra of the terpolymers exhibit strong absorptionsin the region 2800-3300 crrr ' assignable to 8 NHmodes and a medium band at 2650 cm-1 attributableto hydrogen bonded phenolic-OH group. A strongband at 856 cm-1 has been assigned'! to vC= S. Theband observed at 1608 cm-1 in the spectra ofterpolymers may be due to vC= N12. A broad bandaround 3290 cm-1 may be assigned to vNH ofthiourea unit'". The weak band observed in theregion 2500-2600 cm-1 may perhaps be due to thepresence of thioenolic form14 (I).

PATEL & MANAVALAN: SYNTHESIS & CHARACTERISATION OF TERPOLYMERS

SALICHIC ACID: THIOUREA (1:1)

-©rCOOHOH~ ~oCOOHOH ~ &~_CH .NH-C-NH-CH

Z-eOr)....l.8J- CHz-NH -C-~-CH2~CHZ

2 CHI 2NHC;::S

\I ~H

SAlICVllC ACID:THIOUREA .t a n )

III

Though it is difficult to assign exact structures tothese terploymers, considering the linear structureof SF polymers and cross-linked nature of urea orthiourea-formaldehyde homopolymers, the mostfavourable and possible structures (II and III) canbe assigned for the terpolymers.

The conductometric titration method revealed theratio of salicylic acid and thiourea as approximately1 : 1 (Table 1) for those polymers which wereprepared from equimolar proportions of salicylicacid and thiourea. Hence, Mn repeating unit presentin these 1 : 1 terpolymers may be taken as 238 g/rnolby considering the average repeating unit as thione orthioenolic form I.

The terpolymers are thermally stable upto 260°Cand slowly decompose i-- 250°C. The decompositionis rapid at 300°C and is complete at 600°C when80-90 % mass loss is observed. Comparison of thethermal behaviour of polymer sample reveals thatthe polymer samples prepared in presence of eitherHCl or H2S04 as catalyst are more stable than thoseprepared in the presence of glacial acetic acid. Thekinetic parameters have also been calculated from thethermogramsv and are presented in Table 2. Fromthe results of the kinetic parameters it can be conclu-ded that all these polymer samples follow approxi-mately the same mechanism of degradation.Degradation of terpolymers appears to be almostentirely due to breaking of methylene links". Theenergy of activation ranges from 13.17 to 22.3 kJmol+' which is lower than the values recorded in theliterature-",

It is very difficult to draw any conclusion from themagnitude of thermal activation energy because the

Table 2-Results of the Thermogravimetric Analysis ofSTT Terpolymers

Terpolymer Initial decompositiontemp Cc)

240260240220240240240220250220150140150

20.2517.6118.4522.3015.5614.6920.2519.2813.1715.3114.1417.4913.93

Activation energy inkJ rnol'<

1laIblc1d23456789

decomposition mechanism is expected to be verycomplicated 17.

Acknowledgement

The authors wish to express their gratitude toProf. S. R. Patel, for his valuable suggestions. Oneof the authors (RM) is grateful to the UGC, NewDelhi for the award of a teacher fellowship underFaculty Improvement Programme.

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