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Indian Journal of ChemistryVol. 28A, January 1989, pp. 55-58
••Synthesis & Characterization of Terpolymers ofSalicylic
Acid & Dithiooxamide with Trioxane
TUSHAR KANTI PAL & R B KHARA1'"Department of Chemistry,
Institute of Science, Nagpur 440 001
Received 12 January 1988; revised and accepted 17 March 1988
Terpolymers have been synthesized by the condensation of
salicylic acid (S) and dithiooxamide (rubionic acid) (R)with
trioxane (T) in the presence of acid catalysts using varying molar
proportions of the reactants. Compositions of theterpolymers have
been determined by elemental analysis. The number average molecular
weights (Mn) have been de-termined by conductometric titration in
non-aqueous medium. Intrinsic viscosities of the solutions of the
terpolymershave been determined in dimethylformamide. Thermal
behaviour of each terpolymer has also been studied by
thermo-gravimetricanalysis (TGA). The terpolymers have been
characterized by studying their IR spectra, reflectance
spectra,absorption spectra, X-ray diffraction patterns and
electrical conductivities.
Salicylic acid-formaldehyde polymers have foundmany
applications':". The terpolymers of hydroxy-benzoic acid,
urea/thiourea and formaldehyde/tri-oxane have been widely
investigated because oftheir numerous applications=P. Their
ion-exchangeproperties and semiconducting properties have alsobeen
studied. However, a literature survey revealedthat no terpolymers
have been synthesized from sal-icylic acid, dithiooxamide and
trioxane. Therefore,we have carried out synthesis and
characterizationof these terpolymers and the results of our
studiesare reported in the present paper.
Materials and MethodsAll the reagents used were of either AR or
chemi-
cally pure grade. DMF was used after distillation.
Preparation of terpolymersThe polymerization reaction was
carried out with
different concentrations of salicylic acid, dithiooxa-mide and
-trioxane; the details are given in Table 1.Condensation of the
reactants was carried out in thepresence of an acid, like 2M HCI by
heating at130°C on an oil-bath for four hoursv+'. The separat-
ed polymer was washed with hot water and finallywith ether to
remove excess of acid monomer andsalicylic acid-trioxane polymer.
The polymer waspurified by dissolving it in 10% NaOH and
repreci-pitating it by dropwise addition of 1 : 1 (v/v) HCliwater.
The process was repeated twice. The terpo-lymer sample thus
obtained was washed with boilingwater, dried and kept in vacuo over
silica gel. Theterpolymers (SRT) thus synthesized were obtainedin
quantitative yields.
Results and DiscussionAll the terpolymers are light brown in
colour and
soluble in DMF, and aqueous sodium and pota-ssium hydroxides.
The melting points are found tobe in the range ISO-200°C. All the
terpolymers wereanalysed for carbon, hydrogen, nitrogen and
sul-phur. Nitrogen was estimated by Kjeldahl's methodand sulphur as
barium sulphate by Carius method(Table 1). The number average
molecular weights(Mn) were determined by conductometric
titrationsin DMF using ethanolic KOH as the titrant!'. Fromthe
plots of specific conductance against milliequiv-alents of titrant
base added, the first break and the
Table I-Elemental Analysis Data
Terpolymer FoundIcalc.), % Av.mol wt of ["limo.resin ratio
repeating (dig-I)
C H N S . unit
S:R:T 44.67 3.65 10.14 24.28 282 0.05(I: I :2) (46.80) (3.54)
(9.92) (22.69)
S:R:T 51.78 3.92 7.10 15.72 432 0.05(2: I : 3) (52.77) (3.70)
(6.48) ( 14.81)
S: R:T 54.56 3.58 4.86 10.96 595 0.05(3: \: 4) (56.4 7) (3.86)
(4.70) ( 10.75)
55
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INDIAN J CHEM,JANUARY 1989
last break were noted (Table 2). The degree of po-Iymerisation
(DP) of the terpolymers was obtainedfrom the ratio of total
milliequivalents of base usedfor neutralization of all the COOH
groups to themilliequivalents of base used for neutralization
offirst COOH group (first break). The value of (DP)was multiplied
by the average molecular weight ofthe repeating unit to get the
number average molec-ular weight (Table 2).
Intrinsic viscosity measurements were carried outin DMF at 30°C
using a Tuan Fuoss viscometer.Time of flow of DMF was found to be
545 sec. Thereduced viscosity of 3.0% solution of the terpolyrn-ers
was found to be 0.12 dUg. It decreased to about0.02 dUg when the
concentration of the solutionwas reduced to 0.5%. Intrinsic
viscosity ( rJ ) was de-termined by the Huggin's (Eq. 1) and
Krammer's(Eq. 2) relations:
rJs/C = [rJl + K1[rJF C ... (1).In rJ/C = [rJl- K2[rJ)2 C ...
(2)
In accordance with the above relations the plotsof rJs/C and In
rJ /C against C were linear givingthe values of [rJ lnt which were
in close agreement(Table 1)9-12,14,15.
The IR spectra of all the. terpolymers are broadlysimilar;
however, certain small but definite differ-ences are observed. A
broad band, containing sever-
Table 2 - Molecular Weight Determination byConductometric
Titration
Terpolymer First stage of Final stage of Deg. of Mol.resin ratio
neutralization neutralization polLm. wt
(meq/100 g (meq/100 g (DP) (Mn)of terpolymer of terpolyrner
resin) resin)
S:R:T Y2 1472 - 16 4500(I: I :2)
S:R:T Y2 1380 15 6'500(2: I: 3)
S:R:T 92 1564 17 10100(3: I :4)
al inflections, appearing in the region 2400-3400em -1 may be
assigned to the vOH of the interrno-lecularly hydrogen bonded
phenolic group andvOH of - COOH from different acid units in a
po-lymeric chain. The spectra show a number of bandsaround 800,
1300 and 3200 em - 1 which may beascribed to methylene groups. A
sharp band at -1650 em-} is assigned to vC = 0 vibrations ofCOOH
groups". Bands at about 840 and 1075cm - 1 have been assigned to vC
= S. A mediumbroad band at about 3400 em - 1may be assigned tovNH.
The presence 'of amine group is further sup-ported by the ONH2 band
at 1610 ern -1.
The kinetic parameters for the thermal degrada-tion of all the
terpolymers have been calculatedfrom the thermograms and are
presented in Table 3.From the results of the kinetic parameters it
is con-cluded that the terpolymers prepared from a highermolar
ratio of salicylic acid show a lower rate of de-composition
indicating higher thermal stability ofthe terpolymer; the
stabilities follow the order: SRT(3 : 1 : 4) > SRT (2 : 1 : 3)
> SRT (1 : 1 : 2). This maybedue to the possibility of an almost
linear structurein the terpolymer having a higher molar ratio of
sali-cylic acid which may give rise to a stable structure ofthe
polymer chain. This is supported by the highermelting point of the
terpolymer with higher molarratio of salicylic acid. The
terpolymers are thermallystable up to 200°C. Mass loss in all the
terpolymersstarts after 200°C and occurs in three stages. The
in-itial and final decomposition ranges are summarisedin Table 3.
The initial mass loss may be due to theloss of solvent or moisture
entrapped in the terpo-Iymer. The Sharp-Wentworth method was
appliedto the TGA data to determine the energy of activa-tion and
the order of reaction 17-19.The comparativevalues of the onset
decomposition temperatures ofthe terpolymers show the highest value
for SRT(3: 1: 4).
Reflectance spectra in solid phase showed Amax at290 nm tor all
the terpolymers. The observed bandis due to charge transfer of the
type n -> n', The ab-sorption spectra in DMF showed three bands
at
Table 1- Thermogravimetric Analysis
Terpolymer Mass loss at temp. T (OC),% Dec. Energy of activation
Order ofresin ratio temp. (k cal/mol) reaction
100 200 300 400 500 550 (0C) TJ1'1£, 1'1e,
(225-300°C) (300-550°C)
S: R: T (J : I :2) 0.0 1.5 37.0 45.5 49.5 51.5 220 14 0.5,
S : R: T (2: I :3) 1.0 4.5 36.0 43.0 4H.O 50.5 228 20
1.0S:R:T(3: I :4) 2.5 5.0 33.5 39.0 45.0 4H.0 240 14 2.0
56
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PAL et al.:TERPOl YMERS OF SALICYLIC ACID & DITHIOOXAMIDE
WITH TRIOXANE
Table 4-Position of Most Intense Peak in the Amor-phous Patterns
of Various Linear SRT-Terpolymers
Terpolymer d = A.12 sin (J R = 5 U8 sin (Jresin ratio
S:R:T(I:I:2)S:R:T(2:1:3)S:R:T(3:1:4)
3.853.853.86
4.814.814.82
312, 308 and 270 run for all the terpolymers. Theterpolymers
containing thionyl groups and havingdouble bonds separated by two
or more singlebonds exhibit bands due to n -+ st" transitions in
therange 300-350 run. Thus, the reflectance spectra ofthe
terpolymers gave nearly the same bands as wereobtained in their
electronic spectra in solution indi-cating thereby no dissociation
of the terpolymer insolution. The slight shifting of the band
observed inthe absorption spectrum may be due to solvent
ef-fect.
X-ray diffraction studies were done on a PhilipsPW 1700
instrument using copper K, radiation at aspeed of 2° per min. Fine
powder was used for re-cording the patterns. The lattice dimensions
showthat the terpolymers are amorphous in nature. Fromthese XRD
patterns it is observed that the terpolym-ers have a broad band
(halo) characterised by maxi-mum intensity at particular d values.
In other words,it is the strongest innermost peak which is
principal-ly due to interatomic vectors between the adjacentchains.
The interchain separation from the positionof the .first
diffraction maximum was calculated bythe formula, R = 5./8 x A/sin
(). This interatomicdistance (R) responsible for a strong maximum
inthe diffraction pattern at angle () is equal to 1.25times the d
spacing calculated with the aid of theBragg equation, 2d sin ()=
nA. Table 4 shows thevariations in the d spacings+?".
These terpolymers have been further character-ised with respect
to their semiconducting propert-ies. To study the semiconducting
nature, DC resis-tivity was measured using a BPL (India) Million
Me-gohmmeter in the temperature range 300-400 K.Temperature
dependence of the electrical conduc-tivity predicts that all the
terpolymers are semicon-ducting in nature {Fig. 1 )20-23.
The polymers under study are terpolymers andhence it is very
difficult to assign their exact struc-tures. The most probable
structure for the SRT-ter-polymers is a linear or a sparse-branched
linearstructure (I) keeping in view the structure of
salicylicacid-trioxane polymer and crosslinked nature
ofdithiooxarnide-trioxane homopolymers.
Conductometric titration shows that the ratio ofsalicylic acid
to dithiooxarnide is approximately
TER~Lyt,tERA SRT 1:1:2B SRT 2:1:3C SRT 3:1:4
VALUE Of A E in eV0'430-510·58
'0 -10-501o-'
-11-0
-11·5
-12·0
2·7 2·8 2·9 3·0 3·1 H 3·3 3-4
3 1~(K-)
TFig. I-Conductivity variation with temperature
4COOH~ «'60H~
I " I:--... CH2-NH-~-~-NH-CH2' 2-NH'1r-~-NH-CH2 _
S S S sOR
eOOH eOOH
hOH AOH~eH:z-NH-e-e-N-e>f2-0-eH:z_
H II IS S CH:z
INHI
s,eI
S: CI
NHIeH2
I
1 : 1 (Table 1) for the polymers prepared from theirequimolar
proportions.
Hence, an average molecular weight of repeatingunit present in
the terpolymers (1 : 1 : 2 ratio) maybe taken as 282 g mol- I by
considering the averagerepeating unit as structure 1.
AcknowledgementThe authors express their gratitude to Prof.
(Mrs)
Y.M. Sapkal, Director, Institute of Science, Nagpur,for
providing laboratory facilities.
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INDIAN J CHEM, JANUARY 1989
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