Indian Journal of ChemistryVol. 22A, May 1983, pp. 390-394

Synthesis & Characterization ofSalicylic Acid-Urea-Formaldehyde Copolymers

R M JOSHI & M M PATEL*

Department of Chemistry, Sardar Patel University, Vallabh Vidyanagar 388120

Received 28 July 1982; revised and accepted 9 December 1982

Salicylic acid-urea-formaldehyde (SUF) copolymers have been prepared in the presence of different acidic catalysts usingdifferent molar proportions of the reactants, and characterized. Copolymer composition has been determined by elementalanalyses and conductometric titration in pyridine medium against tetra-n-butylammonium hydroxide. The number averagemolecular weights (M.,) have been determined by conductometric titration in nonaqueous medium and vapour pressureosmometry. Copolymer prepared using equal molar proportions of the reactants and hydrochloric acid as a catalyst exhibitshighest molecular weight in the series. Viscometric measurements in dimethylformamide (DMF) have been carried out with aview to ascertaining the characteristic functions and constants. TGA and differential scanning calorimetry data have beenanalyzed to compare the relative thermal stability and estimate some of the parameters. IR spectra have also been recorded toelucidate the structure.

In an earlier paper we reported the preparation andcharacterization of metal chelates of salicylic acid-urea-formaldehyde (SUF) copolymers '. In view of theinteresting characteristics especially ion exchangingproperty and many other industrial applications ofcopolymers obtained by the condensation ofphenol/hydroxybenzoic acid and urea/urea derivativeswith formaldehyde! --5, we report in this paper thesynthesis and characterization of salicylic acid (S)-urea(U)-formaldehyde (F) copolymers.

Materials and MethodsAll the chemicals used were obtained from Sarabhai

Merck or BDH and used as such except DMF whichwas used after distillation.

Preparation of copolymers-The polymerizationwas carried out at different concentrations of salicylicacid, urea and formaldehyde, the details are given inTable I. Condensation of the reactants was carried outin the presence of acids like 2M HCI (method-A), 2MH2S04 (method-B) and glacial acetic acid (method-C)separately at 100° for 5 hr. The details of thepreparation and purification are same as reportedearlier", The copolymers prepared by methods (A) and(B) were obtained in quantitative yields while the yieldin the method (C) was .-75%.

Fractionation-Copolymer sample SUF-I (Table I)(lOg) was dissolved in DMF (500m!) fractionated at32° by fractional precipitation method and the fourfractions were collected by the method described in anearlier paper". The first fraction was collected afteraddition of 1M H CI (450 ml) to the original copolymersolution and the second, third and fourth fractionswere collected by adding about 350, 400 and 600 ml1M HCI to the first, second and third filtrate

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respectively. The first, second, third and fourthfractions amounted to 1.6, 2.0, 2.3 and 1.1 grespectively.

Results and DiscussionAll the copolymers were light brown to white.

Copolymers prepared from salicylic acid and urea in amolar ratio greater than I: I were completely soluble inDMF, pyridine, aq. NaHC03 and aq. NaOH whilecopolymers obtained using S:U molar ratio of I: I wereabout 95~()soluble in above solvents. Neutral solutionof each copolymer reacted with Fe3+ to give violetcolour. Melting points of copolymers were found inthe range 170 -220 .

The results obtained for copolymer composition bynitrogen estimation and conductornetric titration innonaqueous medium 7 (pyridine) against tetrabutyl-ammonium hydroxide were in good agreement (TableI). On the basis of nitrogen per cent in the copolymersamples, copolymer composition could becalculated'':" since only one monomer (urea) containsnitrogen. The results indicated that the copolymerprepared (from equimolar proportion of (S) and (U)have almost the same composition.

The results of conductometric titration were alsoused to determine the number average molecularweight (MJ of the copolymers (Table 2). From theplots of specific conductance against milliequivalentsof titrant base added, the first breaks and the lastbreaks were noted (Table 2). The degree ofpolymerization (DP) of the copolymer samples wereobtained from the values of the breaks".

Molecular weights (MJ of copolymers were alsoestimated by vapour pressure osmometry (VPO)(Table 2). The molecular weights of copolymer samples

JOSHI & PATEL: SALICYLIC ACID-UREA-FORMALDEHYDE COPOLYMERS

Table I-Synthesis of Copolymers and Their Compositions

Copolymer Mol ratio of N(u.,l* Copolymer composition; Av. mol wt ofreactants repeating(S:U:F) (S) unit (U) unit unit

Method (A) employed for preparation

SUF-I 1:1:2 12.31( 12.34)t 0.509 0.491 111.68SUF-2 1.5: I:2.5 983(10.01) 0.587 0.413 117.66SUF-3 3: 1:4 7.31 (7.67) 0.675 0.325 124.61SUF-3a I304{ 13.51) 0.488 0.512 109.9SUF-3b 12.54{ 13.22) 0.502 0.498 111.16SUF-3c 12.14{ 12.93) 0.514 0.486 112.10SUF-3d 1173(1263) 0.526 0.474 113.00SUF-4 1:1:1 12.59(14.09) 0.501 0.498 111.00SUF-5 1:1:4 14.07(13.51) 0.458 0.541 107.65

Method (B) employed for preparation

SUF-6 1:1:2 13.26( 13.22) 0.481 0.518 109.44SUF-7 1.5: I :2.5 10.31(10.30) 0.570 0.429 116.38SUF-8 3:1:4 7.45 (7.38) 0.670 0.330 124.11SUF-9 1:1:1 12.83( 1176) 0.493 0.506 110.38SUF-IO 1:1:4 12.53( 1338) 0.503 0.497 111.08

Method (C) employed for preparation

SUF-II 1:1:2 17.34{ 17.01) 0.373 0.626 101.02SUF-12 1.5:1:2.5 13.72(13.51) 0.468 0.532 108.50SUF-13 3: 1:4 10.17(10.88) 0.575 0.424 116.78SUF-14 1:1:1 16.85(17.01) 0.385 0.614 102.00SUF-15 I: 1:4 18.12( 19.92) 0.372 0.628 101.00

* An error of nearly 2% in the reported value has been noted on an average.t By conductometry.:j: Compositions are expressed in mole (m) ratios and obtained by the use of N estimation (Micro Duma's method).

Table 2-Molecular Weight Determination

Copolymer Conductometric titration VPO

First break Final break DP Mol wt. Mn( ± 5-8'/,',) OP(meq/IOOg (meq/IOO g (Mn±5%)

of copolymer) of copolymer)'

SUF-I 50 446(455) 9.1 1016 1100 9.85SUF-2 70 495(498) 7.1 835 730 6.2SUF-3 100 535(541) 5.41 674 580 4.65SUF-3a 40 434(443) 11.07 1.220 1270 11.55SUF-3b 45 440(451) 10.00 1111 1030 9.26SUF-3c 60 445(458) 7.63 855 780 6.96SUF-3d 85 452(465) 5.47 618 510 4.51SUF-4 55 424(451) 8.2 910 830 7.47

SUF-5 65 435(425) 6.54 704 600 5.57SUF-Ii 45 440(439) 9.75 1067 990 9.05SUF-7 65 490(489) 7.52 875 780 6.70SUF-8 105 540(539) 5.13 636 570 4.59SUF-9 60 465(446) 7.43 820 800 7.25SUF-IO 80 420(452) 5.65 630 560 5.04SUF-II 40 375(369) 9.22 930 920 9.10SUF-12 70 435(431) 6.15 670 630 5.80SUF-13 100 480(492) 4.92 575 520 4.45

SUF-14 45 375 (377) 8.37 853 790 7.74SUF-15 65 325 (356) 5.47 552 500 4.95

* Values in parentheses are by nitrogen estimation

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INDIAN 1. CHEM., VOL. 22A, MAY 1983

Table 3-Viscometric and DSC Data[II] x 102(dl.g -I) Huggin's Kraemer DSC

constant constantEq. (I) Eq. (2) K, K' T.Cc) m.ptC) Heat of fusion,

(kcal.mg)

6.620 6.64 0.913 -0.326 84 209 6.535.80 5.80 0.832 -0.243 105 196 8.985.42 5.42 0.766 -0.270 101 17l 9.307.14 7.16 0.882 -0.324 101 217 10.476.82 6.82 0.63 -0.080 101 215 9.976.64 6.61 0.413 +0.106 102 209 12.205.42 5.45 0.474 +0.051 102 184 13.575.87 5.84 0.656 -0.099 83 192 8.336.49 6.50 0.878 -0.303 105 196 9.066.58 6.58 0.510 -0.007 105 196 12.126.13 6.16 0.522 -0.084 91 194 19.545.36 5.37 0.769 -0.239 86 I54(d) No endotherm6.2} 6.21 0.613 -0.0656.10 6.10 0.683 -0.151 105 I99(d) No endotherm6.20 6.24 0.425 +0.055 101 184 15.055.47 5.47 0.688 -0.125 101 I78(d) No endotherm4.95 4.99 0.673 -0.122 101 189 15.666.09 6.11 1.149 -0.5425.77 5.78 0.463 +0.073

Copolymer

SUF-ISUF-2SUF-3SUF-3aSUF-3bSUF-3cSUF-3dSUF-4SUF-5SUF-6SUF-7SUF-8SUF-9SUF-IOSUF-IISUF-12SUF-13SUF-14SUF-15

(d) Melting followed by decomposition

estimated by conductometric titration and VPOmethod are comparable within limits of experimentalerror. The results of the molecular weight ofcopolymer samples revealed the following trends:(i) copolymers prepared using equal molar proportionof the reactants showed comparatively highermolecular weights. (ii) The molecular weights of thecopolymers in terms of catalyst used were in the order:HCI~H2S04 > CH3COOH. Thus, CH3COOH iscomparatively a weak catalyst in the copoly-merization.

Viscometric measurements (Table 3) were carried outin DMF at 35° using Ubbelohde viscometer. The rateof decrease in reduced viscosity with the decrease inconcentration of the solution was lower in thecopolymer prepared from higher proportion ofsalicylic acid than urea. Intrinsic viscosities [11J weredetermined following Huggin ' 0 (Eq. I) and Kraemer"(Eq. 2) rela tions:

l1,p/C=[I1J+K, [I1J2C

In I/,IC = [11J - K', [r/J2C

In accordance with the above relations the plots of11,p/Cand In I/,IC against C were linear giving the slopesK, and K', respectively. Intercept on the axis ofviscosity function gave [11Jvalue in both the plots. Thecalculated values of constants K, and K', (Table 3) inmost of the cases satisfy the relation K, + K', = 0.5favourably ' 2 The values of [1/J obtained from Eqs (I)and (2) were in close agreement. The trend in intrinsic

392

viscosities is the same as the trend in molecular weightsdescribed above. Intrinsic viscosities and molecularweights of copolymers SUF-I and its fractions werecorrelated by Mark-Houwink equation:

'" (3)

The above relation is rewritten as:

log [IIJ = log K + 7.10g(M) ... (4)

(I)

(2)

This Eq. (4) was applied to the data obtained formolecular weights and intrinsic viscosities of fractionsof SUF-I copolymer (Tables 2 and 3). The values of

. constants K( 1.326 x 10 2) and 7.(0.236) (ref. 13) wereobtained from the intercept (y-axis) and the slope of thelinear plot respectively.

IR spectra of all the copolymers recorded in KBrmatrix resembled each other and exhibited all thesignificant characteristics suggested by the structure (I)and (II) assigned to the copolymer on the basis ofnature and reactive positions of the monomer-acid andurea molecules. A broad peak in the range 3500-2800 em -, was assigned to intramolecular hydrogenbonded vOH. Since this broad band covered the regionfor - CH of - CH 1 - and phenyl ring, it was ratherdifficult to assign clearly the methylene bridgefrequencies. However, the inflections at 2880 and 2858(vCH) and a medium band at 1450 due to scissoringmode and also a small but sharp band at 812 ern - ,owing to rocking modes of - CH 2- suggest thepresence of methylene -CH1 - bridges in copoly-mers!". The presence ofa very small but distinct band

JOSHI & PATEL: SALICYLIC ACID-UREA-FORMALDEHYDE COPOLYMERS

at 864 (bCH out of plane) and inflections in the region1000-1200 ern -I (bCH in plane) may be attributed tothe presence of I, 2, 3, 4-tetrasubstitution 14 of thearomatic ring of the repeating unit. A broad bandobserved around 3315 ern -I may be assigned to vNHof urea unit. A medium sharp peak at 1600 ern -I maybe ascribed to aromatic skeletal ring breathing modes.The band recorded at around 1675 ern -I may be dueto vC=O of both the acid and urea molecules!". Thecopolymers in the present study contain threemonomers and hence it is rather difficult to assignexact structure to them. However, on the basis of thenature and reactive positions of the monomers andtaking into consideration the linear structure of othersubstituted phenol-formaldehyde polymers8.9.15 andlinear branched nature of urea-formaldehydepolymers 16, the structure proposed for the copolymersmay be of two types: Linearly branched structure (I)which may sparsely cross-link through N-atom of ureaunit and linear structure (II). Thus, the distribution ofmonomer units along the polymer chain would berandom.

The TG and differential scanning calorimetry (DSC)thermo grams of some selected copolymers wererecorded on a Linseis thermal analyzer (WestGermany) and Du Pont analyzer (USA) respectively.

The initial and final decomposition ranges aresummarized in Table 4. Parts of the initial mass lossesmay be due to the solvent or moisture entrapped in thecopolymer. The copolymers prepared from highermolar ratios of S:U showed lower rate ofdecomposition in the beginning up to 2000

, suggestingthe stability order: SUF-3 > SUF-2 > SUF-1. Thismay be due to the possibility of almost linear structurein the copolymer due to higher content of SF-unitwhich may give rise to a stable configuration to thecopolymer chain. Among the copolymers preparedfrom equal molar ratios of the reactants(S:U:: 1:1)HCI-catalyzed copolymer has the highest stability. TheBroido method 17 was applied to the TG data todetermine the energy of activation and an order of thereaction. There is no significant difference in energy ofactivation of the copolymers. The order of reaction atthe first and second stages of decomposition wascalculated to be unity.

DSC thermograms of copolymer samples showedthe two broad endothermic peaks. The endotherm atthe lower temperature site may be assigned to glasstransition temperature (Tg) (Table 3) as generallyobserved in sloping nature from the very beginning ofthe curve in the case of amorphous polymeric materialsand the second endotherm at higher temperature maybe due to melting of the copolymer.

The peak area of the latter endotherm was used tocalculate heat of fusion by substituting in the equationreported in the literature 18. All thermograms wererecorded by taking the sensitivity ofx and y axis, equalto 50c linch and 0.20linch respectively at a heating rate,20c /min. DSC data (Table 3) revealed that as the (S)content in the copolymer decreased, the m.p. of thecopolymer also registered a decrease. A reverse trendwas observed in the glass transition temperature.

AcknowledgementThe authors wish to express their gratitude to Prof.

S.R. Patel, for his valuable suggestions. One of the

Table 4- TGA Data of Copolymers

Mass loss % at Decomp. range, (eC) EO' kJlmol

100° 200e 300e 400' 5000 600cC First Second First Secondstage stage stage stage

5.98 31.62 52.13 81.19 82.05 82.05 60-320 320-460 18.25 31.656.54 38.31 54.20 77.57 83.17 83.17 60-220 220-500 20.22 26.173.87 14.73 64.34 79.84 80.62 80.62 60-240 240-440 23.11 14.957.53 34.40 59.14 75.26 80.64 80.65 60-140 140-420 28.72 15.455.40 41.89 63.51 79.72 82.43 82.43 60-220 220-480 34.21 20.185.00 41.66 59.16 78.33 80.00 80.00 60-220 220-460 18.63 34.548.06 39.23 64.39 83.33 83.33 83.33 60-320 320-460 18.25 31.6912.82 37.18 87.95 79.48 80.77 80.77 60-160 160-420 30.69 19.807.21 35.05 59.79 79.38 80.41 80.41 60-150 150-440 31.23 22.98

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Copolymer,

SUF-ISUF-2SUF-3SUF-3aSUF-3bSUF-4SUF-5SUF-6SUF-II

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

authors (RMJ) is grateful to the UGC, New Delhi forthe award of a research fellowship under facuItyimprovement programme.

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