Indian Journal of Chemical Technology Vol. 6, July 1999, pp. 219-224

Polymer alloy of poly (metal acrylate)

Pragyan Mohan & A K Srivastava*

Department of Chemistry, Harcourt Butler Technological Institute, Kanpur 208 002, India

Received 8 September 1997; accepted 9 June 1999

A series of different type of polymer alloys has been prepared by the combination of poly (acrylonitrile) (PAN) and poly (bismuth acrylate) (PBiA)/poly (arsenic acrylate) (PAsA). The metal forms a complex with the nItrogen of poly (acrylonitrile), as evidenced from IR and FfIR spectroscopy. The higher value of interaction coefficient (kAB)for PBiA-PAN (1.2) in comparison to PAsA- PAN (0.6254), indicates the formation of strong complex and Vander Walls forces between PBiA and PAN macromolecules . The presence of two closed values

( 146, 152QC) for Tg and little phase separat ion in SEM micrographs shows that PAN and PAsA are sufficiently compatible with each othcr. However, the PAN and PBiA are completely compatible as there is no phase

separation in SEM micrographs and h~s single Tg (281 QC).

The scientific and commercial progress in the area of polymer chemjstry, was driven by the realization that the new molecules are not always required to meet needs for new materials, the alloying/blending can usually be implemented more rapidly and econorrucally than the development of new chemistry.

The increasing commercial value of polymer blends have fueled the search for new polymer alloys. The polymer alloys are one of the most prorrusing and important categories of polymers for their end applications. There polymeric rruxtures are capable of realizing a wide spectrum of physico-chemical properties, which depend on the extent of component compatibility. The study of the viscosity of binary solutions comprising a low molecular weight solvent and two chemically dissirrular polymers, has been subject of great interest because it provides useful information regarding stereocomplex formation ,,2.

Although several papers on polymer alloys have been published, most of them describe studies of alloys of polyphenylene ether,l, polyethylene oxide and PMM\ substituting alloys5, PVC and poly (styrene)6, po~y (benzirrudazole) and poly (acrylate)?, rubber-epoxy , PBI/PC/rubber system9 etc. However, there is no published information on the interaction and compatibility of poly (metal acrylate (s». This paper presents the results of such efforts and brings out clearly thi s parameter by using poly (bismuth acrylate) and poly (arsenic acrylate), which are reported for the first time .

*For correspondence

Experimental Procedure

Materials Purified monomers, initiators (azobisisobu-

tyronitrile), acrylic acid, acetone, triphenyl bismuth, triphenylarsine DMSO and DMF have been used as received.

Synthesis of metal acrylate

~ormally, metal acrylate (s) have been prepared IO by the reaction of acrylic acid and metal oxide/carbonate, because of their basic nature. However, bismuth and arsenic acrylate could not be prepared by this method, probably because of amphoteric nature of their oxides and carbonates. The bismuth and arsenic acrylate" have been synthesised by the stirring of the respective triphenyl metal (Bi,As) with acrylic acid in acetone for 22 h. The reaction scheme is as follows ,

T*(for Arsenic acrylate 312°K, for bismuth acrylate 273°K)

m.p. (PAsA = 316° K, PBiA = 346° K). Structure evidence for metal acrylate comes from

IR and NMR spectroscopy . Infrared spectrum was recorded in KBr pellet form, on a Perkin Elmer Model 377 Spectrophotometer.

2990 -3000 cm"(C-H, Alkene Stretching) 900 cm"(Alkene bending) 1680 cm"(Carboxylation) 'HNMR spectrum was recorded on Varian EM-390

spectrophotometer using tetramethylsilane (TMS) as internal standard.

220 INDIAN 1. CHEM. TECHNOL., JULY 1999

---A 8 -8

..;. 60 __ r __ "",- ______ - ...... "'" .... ,"'-", .... """"',

CII u C 0 --E 4O III C 0 L..

~

20

-1 WavGlnumbGlr, ern

I', I,~ :: ' 1,1 I , I I" , I ,

I.' I ~ I I I ",- " • ~ '..J'

Fig I-IR spectra of poly acrylonitrHe (----), poly (arsenic acrylate) (---)

8

--E ~ 4 o L..

~

20

~O~O~O---L--~18~O~O--~---1~6~OO~~--~1~400 -1 Wavenumber ,em

Fig 2-IR spectrum of poly bi smuth acrylate.

2-38 (m.CH2 protons) 6-78 (m.conjugated CH2 = CH protons)

Synthesis of poly (metal acrylates) Bismuth ac rylate and arsenic acrylate were

pol ymeri zed by using styrene-arsenic sulphide complex 12 in DMSO as the radical initiator at 80 ± I DC for 10 hand 20 h respective ly. The structure of the pol ymetal acrylate (s) is as given below,

Polymerization of acrylonitrile Acrylonitrile was polymerized by using

azobi sisobutyronitrile as radical initiator and DMF as

inert solvent at 60 ± 10 C for 90 min under an inert atmosphere of nitrogen .

Synthesis of polymer alloy Polymer alloys were prepared by dissolution

method l, , Poly (metal acrylate) was dissolved in

toluene (10% wt./volume) and then added to poly (acrylonitrile) (10% wt./vol. in DMF). The miixture was stirred for 12 h. The polymer solution was cast onto borosil glass petridishes and the solvent was evaporated at 50DC for 58h. under vacuum .

Characterization of polymer alloy To find out the strength of interaction between the

polymers, the interaction constant kAB of mixture of stereocomplexes of pol ymers (i.e . PAN & PBiA, PAN & PAsA) was evaluated by viscosity studies . The soluti ons used in viscosity measurements were prepared as reported earlier l4

.

The polymer, whose solution was used as solvent, was di ssolved to give a series of solutions having concentration ranging from 2.5 x 10-4 to lO x 10-4 gm cm- ~ . After di ssolution and filtrat ion, the second polymer (concentration lO x 10-4 g cm-') was di ssolved in these soluti ons_ According to "Polymer Solvent" method I5

-17

, the intrinsic viscosity of polymer A, [ll A]s is determined in a number of various concentrated soluti ons of polymer B, which

serve as solvents and vice versa. [llA]s was calculated b . 14

Y an equation

where [ll r1o=re lative viscosity of the polymer B at the concentration Cw [ll A] and [lls]=intrinsic viscosities of the polymer A and B in a pure solvent and - kAS=Constant of interaction between macromolecul es A and B.

The interaction coefficient between polymers has been obtained from the plot off [ { ( [ ll A 10 1 [ llr 1s 1 [llA] ) - I } 12] versus the reduced concentration C = [lls]Cs' which gives directly kAS from the intercept on the Y ax is. The case where the polymer B is the dissolved compound and the solution of the polymer A is the solvent, is treated similarly and gives the same value (kAS = kSA) '

SEM-Scanning electron microscope (SEM) was used to observe morphological structure of alloy. SEM was carried out on JEOL JSM 840 A scanning electron microscope. The film was mounted vertically on an SEM stub using silver adhesive paste.

...\-

MOHAN & SRIVASTAVA: POLYMER ALLOY OF POLY (METAL ACRYLATE) 221

80

20

--- A -8

-1 WQv~numb~r I em

Fig 3-IR spectra of (PAsA-PAN) alloy (---), (pBiA-PAN) alloy (---)

~·~--~~~--~&SO~0~~--~1S~00~--~--~0 Wavenumbcl' ,em'

Fig 4-FTIR spectrum of poly (acrylonitrile).

DSC-Differential scanning calorimetry was employed to investigate-the compatibility of polymers in alloys. DSC was recorded on a V2 - 2A Du-pont 9900 differential scanning calorimetry under nitrogen atmosphere at heating rate of I.O°C/min. The sample weights were 3-5 mg.

Detection of metals The ash of alloys was prepared by heating samples

at 400°C in muffle furnace and then tested Bi and As qualitatively.

Results and Discussion Structural evidence for polymer alloys comes from

the IR and FTIR spectrum. Figs 1,2 indicate the characteristic frequency of a cyanide group (- C == N)

150

.. ~ I: c 2100

E .. c e ....

20L--....,3>iSOO;;;:;---~----,;1l<:n----'------u1500t;;;,--~-----.5~OO Wavenumber, em'

Fig 5-FTIR spectrum ofPBiA-PAN alloy.

at 2260 cm- I for PAN and a carboxylate group (-C 00) around 1600-1700 cm- I for PBiA and PAsA. The PBiA-PAN interaction was revealed with the aid of IR spectrum (Fig. 3) which is based on the cyanide stretching of a pure PAN and alloy film. The area ratio of cyanide and carboxylate bands from the IR spectra is 0.1:1.0 for PBiA-PAN and 0.3 :1.0 for PAsA-PAN, while from the original polymers PBiA : PAN and P AsA : PAN is I : 1. FTIR spectra (Figs 4-6) show a dramatic downfield shift from 2244 to 2241.5 cm-I

, 2244 to 2243 cm- I for PBiA­PAN and PAsA-PAN film respectively. This shift indicated the existence of some type of interaction between PBiA - PAN and PAsA - PAN. The downfield shifting of cyanide frequency in PBL~­PAN macromolecules is greater than that of PAsA­PAN macromolecule. This result indicate that only few cyanide groups are involved in some type of bonding and they are not free l8

. The bonding may be due to complex formation between C == N (lone pair

of nitrogen) and metals (As, Bi) and Vander Waals forces, as reported earlier for other metals l9

.

The possible structure for complex is,

where M = As, Bi, 111 + 112 = 3.

The condition for obtaining the coefficient kAB (for PBiA-PAN and PAsA-PAN systems) by the viscometric measurement is a linear dependence of the intrinsic viscosity of solution of polymer mixture on weight fractions of the polymer components (additivity of their intrinsic viscosities). The method of "polymer solvent" reflects, changes in the molecular dimension of molecules of polymer A due

222 INDIAN 1. CHEM. TECHNOL. . JULY 1999

65L-~3~~O--~----o.5~--~--~~n---~--~SOO~ Wovenumbc.r ,em1

Fig 6-FTIR spectru~ of PAsA-PAN alloy.

f

0·5

0-0 0·2 0-4 0·6 0-8 "C

Fig 7-Dependence of the parameter f on the reduced po lymer concentration C. 0 - PAN solute. F 8 iA solution as solvents; e­PBi A solute. PAN so lution as solvent, D - PAN solute. PAsA so luti on as so lvent s: .-PAsA so lute. PAN solution as solvent.

to the molecul es of the po lymer B and is more re liable and exac t in the determination of kAB than direct ca lculati on of thi s value using the interaction constant obtained from measurements of the intrinsic viscos it y of a solution of a mi xture of polymers at a constant rat io of both component. The abil ity of the two po lymers to fo rm a comp lex depends upon the concentration rati o of the polymers in the mixture. on the ir total concent rati on and on time.

Th,c complex formation between unlike polymers has bee n stud ied 14 by the d('terminati on of kAB values. The k .. \1J va lues are assoc iated with the interacti on of un like macro molecules in the fie ld of shear forces and is sim il ar to the Hu ggi ns coeffi cients kA and kn. In

2

Fig. 8-DSC curve of Polyacrylonitrile.

general, the Huggins coefficient on gmates from a superposition of several types of interactions, the hydrodynamic and thermodynamic interaction being the most importan t. The experimental conditions and results have been summarized in Tables 1,2 and Fig. 7.

Complex formation between poly (acrylonitrile) and poly (arsenic acrylate)

In Fig. 7 the interaction parameter (j). defined as a measurement of the hydrodynamic and thermodynamic interac tions is plotted as a function of C in 10% toluene in DMSO (Table I) . The value of the mutu al interacti on coeffici ent k AB (fo r the given system A = PAN, B = PAsA) was determined by ex trapolating these line to C = O. A common intercept was obtained on the Y axi s and k A8 = k8A =

I f l . . I ' h h d' 42021 0.625. The va ue 0 t\ A13 IS llg er t an reporte .. one. These v,liues indicate. that the interaction between PAN and PAsA in vo lves vander waals forces and co mp lex fo rmati on between cyanide group and arseni c in PA l and PAsA, respecti ve ly . Table I reveals th at th e va lu e of [ll pANJPAsA increases as the concentrat ion C of PAsA increases . This indicates that !here is an increase in the dimension of the molecules of PAsA in the presence of PAN.

Complex formation between poly (acrylonit rile) and poly (bismu th acr 'la le)

The complex fo rmation between PAN and PBiA has been studied and results are illustrated in Table 2 and shown in Fig. 7. The stud y of Table 2 reveals that the val ue of [llpAN]p[M increases as the concentration

)-

....

MOHAN & SRIV ASTA V A: POLYMER ALLoy OF POLY (METAL ACRYLATE) 223

Table I-Intrinsic viscosity of polymer solvent in DMSO for PBiA and PAN system.

CPBiA X 10~ [llpAN)PBiA C PAN x I04 [ llpBiA]PAN

. ~ g cm" ~ gem') g em '

2.5 1410 2.5 1660 5.0 1682 5.0 1690 7.5 1710 7.5 1760 10.0 1750 10.0 1809

Table 2-lntrinsie viscosity of polymer solvent in DMSO for PasA and PAN system

CPA,AX 10~ [T) PAN jPA,A CPANX 104

[ T\PAsA]PAN . ~ g cm-J gem') gem '

2.5 954 2.5 1104 5.0 974 5.0 1160 7.5 11 04 7.5 1224 10.0 1095 10.0 1320

C of PBiA increases . This indicates, •.. at there .is an increase in the dimension of the molecules of PBiA in the presence of PAN. From Fig, 7 it is clear thatfis a direct function of C and the values of the mutual iryteraction coefficients kAB = kBA is 1.2. The kAB value is higher in comparison to P AN-PAsA and those

d I' 14 16 17 Th I'd' h h reporte ear ler . " ese va ues In Icate t at t e interaction between PAN and PBiA is higher and involves Vander Waals forces, alongwith strong complex formation between nitrogen of PAN and bismuth of between PBiA, The strength of complex formation between PBiA and PAN, is greater than PAsA and PAN, is due to the less electronegativity and hi gher atomic size of Bi in comparison to As. These results supported the spectroscopic studies of polymer alloys,

DSC studies-It is well known that the degree of miscibility of two polymers can be determined by the glass transit ion temperature. The Tg of pure PAN is 98°C (Fig. 8). The DSC study of P AsNP AN (I: 1) f ilm alloy revealed the existence of two Tg ( 146 and 152°C) at 0,04352 mW heat flow (F ig. 9) . These Tg values are ve ry close suggesting that PAsA and PAN are sufficient ly compatible with each other and perhaps there were two different phases, one rich in PAsA and the other in PAN.

The single Tg value (Fig. 10) for PBiA ., PAN (I: 1) indicates th<it PAN and PBiA alloy are completely miscible with each other. The higher and single Tg value of PBiA-PAN alloy in comparison to PAsA­PAN all oy support d the greater interaction coefficient (kA B) value, for PBiA-PAN alloy

~ E

~ 0

i.:

0 .. :x:

1~r---------------------~-------------.

1-0

()-5

0'0

-0-5

-10() 151-83 t 146·01 t

-1'5 0~-'----'--~--~10;nO ---'-----'----'---;;;4;".--'---'----'--. .,d300

Tampcraturc ', t .

Fig 9-DSC curve of (PAsA-PAN) alloy.

o

-10~---''---''''1~O-,c-O ---'----;;2-;tOO,----'---"30I;;;O---'---~~

TemPQrQtun~ ~ 'c

Fig 10-DSC curve of (PBiA-PAN) alloy.

incomparison . to PAsA-PAN alloy calculated by 'solvent method'.

Morphology-The morphological charactrerization of two phase polymer system is commonly carried out by the use of scanning electron microscope (SEM). Fig. II is a scanning e lectron micrograph of poly (arsenic ac rylate)/poly (acrylonitrile) at an original magnification of 5000 x as a funct ion of incident

beam voltage. The black phase has the low scattering efficien cy, low z number, poly (acrylonitrile) phase . However, the bright or whi te phase has a high z nu mber, high scattering efficiency, arsenic stained poly (arsenic acry late phase). The first white phases (Fig. I I) exhibit a spherical surface. The photograph shows two phase morphoiogies of the PAs A-PAN all oy . This observ:lt io ll is a consequence of DSC results showing two closed Tg' s ( 146-152 0c) which is characteris ti o:.: of a two phase system of polymer alloy of PAsA-PAN.

224 INDIAN l. CHEM. TECHNOL., JULY 1999

Fig II-SEM : Back scattered electron image (BE) of (PAsA­PAN) alloy at a magnification of 5000~.

Fig 12- SEM : Back scattered electron image (BE) of (PBiA­

PAN ) alloy at a magnitieation of 5000x.

Fig. 12 shows the scanning electron micrographs of poly (bismuth acrylate) and poly (acrylonitrile) alloy. In the III alloy are seen clearly dispersed poly (bismuth acrylate) (bright region in figure) in the continuous poly (acrylonitrile) phase (dark region) . It suggests that, in the dynamic vulcanization process of III alloy, phase inversion took place. The fine dispersion of PBiA in PAN matrix may be due to the interaction of cyanide group of PAN and bismuth of PBiA. The result was supported by DSC study and polymer solvent method, showing one Tg's characteristic of completely miscible polymer alloys and high kAB (1.2) value for PBiA-PAN, respectively.

Conclusions (i) Interaction coefficient (kAB) for PBiA-PAN :>

PAsA-PAN. (ii) Interaction was observed around .cyanide (CN)

group of poly (acrylonitrile) and metal (Bi, As) of poly (metal acrylate).

(iii) Polyarsenic acrylate and polyacrylonitrile were sufficiently compatible, however, poly (bismuth acrylate) and poly (acrylonitrile) was completely compatible.

Acknowledgement The authors are thankful to the Director, H.B .T.L,

Kanpur for providing the necessary facilities and Department of Science & Technology, New Delhi for financial assistance in Project SP/SIIG 19/91.

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