Complex-formation in aqueous solutions of mixtures of polyacrylic acid and polyvinylalcohol and its copolymers

Complex-formation in aqueous solutions of mixtures of PAA and PVA

1859

9. S. BRETSZNAJDER, Svoistva gazov i zhidkostei (Properties of Gases and Liquids). 536 pp., Moscow, Leningrad, 1966 (Russian translation) 10. A. WEISSBERGER, E. PROSKAUER, J. RIDDIK and E. TOOPS, Organicheskiye rastvoriteli (Organic Solvents). 520 pp., Moscow, 1958 (Russian translation) 11. V. P. BELOUSOV and M. Yu. PANOV, Termodinamika vodnykh rastvorov neelektrolitov (Thermodynamics of Aqueous Solutions of Non-electrolytes). 265 pp., Leningrad, 1983 12. Ye. G. ATOVMYAN, S. M. BATURIN and T. N. FEDOTOVA, Vysokomol. soyed. B24: 137, 1982 (Not translated in Polymer Sci. U.S.S.R.) 13. D. R. COOPER and C. BOOTH, Polymer 18: 164, 1977 I4. A. KOTERA, K. SUZUKI, K. MATSUMURA, T. NAKANO, T. OYAMA apd U. KAM. BAYASHI, Bull. Chem. Soc. Japan. 35: 797, 1962 15. Ye. G. ATOVMYAN, A. V.LEBEDEVA and G. I. CHERNYI, VysokomoI. soyed. B24: 52, 1982 (Not translated in Polymer Sei. U.S.S.R.)

Polymer Science U.S.S.R. Vol. 31, No. 8, pp. 1859-1866, 1989 Printed in Poland

0032-3950189 $10.00+,00 O 1990 Pergamon Press pie

COMPLEX-FORMATION IN AQUEOUS SOLUTIONS OF MIXTURES OF POLYACRYLIC ACID AND POLYVINYLALCOHOL AND ITS COPOLYMERS* N . G. BEL'NIKEVICH, T. V. BUDTOVA, N . P. IVANOVA, YE. F. PANARIN,

Yu. N. PANOVand S. YA. FRENKEL' Institute for High-Molecular Compounds, U.S.S.R. Academyof Sciences (Received 5 February 1988) The rheological behaviour of dilute solutions of a "polyelectrolytic" mixture of polyacrylic acid and PVA in water at a total polymer concentration of 0. 5 wt.% has been studied. The relationship between relative viscosity and composition of the polymer mixture has been found, in a number of cases, to exhibit positive deviation from additivity with a maximum close to a composition of 20 wt.~/o of polyacrylic acid. In order for the effect to appear, the molecular mass of the polyacrylic acid sample should be abo~e a critical value but the molecular mass of the PVA sample can be artitrary. The observed effects are explained by the supposition that non-stoichiometric polyelectrolytic complexes are formed. Application of model concepts, developed here for the supermolecular organization of the complexes, to the analysis of the experimental data has made it possible to conclude that the most probable organization is a randomly branched macromolecule with trifunctional branching nodes. THE investigation o f processes involved in the f o r m a t i o n o f n o n - s t o i e h i o m e t r i c p o l y electrolytic complexes ( N P E C ) is a m a t t e r of c u r r e n t interest since it opens u p possibilities for o b t a i n i n g p o l y m e r i c systems w i t h new p r o p e r t i e s [1]. T h e f o r m a t i o n o f w a * Vysokomol. soyed. A31" No. 8, 1691-1696, 1989.

N. G. B~L'NI~WCa et al.

1860

ter-soluble N P E C is k n o w n to occur b o t h between oppositely charged polyelectrolytes [1-3] and also between polyelectrolytes and neutra lpolymers such as P E G [2], polyvinylpyrrolidone [4] and P V A [5, 6] but the effect o f the t h e r m o d y n a m i c quality o f the solvent, the concentration o f links with a particular structure, molecular mass a n d other factors on the f o r m a t i o n o f such complexes a n d their structure has been insufficiently studied. These problems are considered in the present w o r k with the interaction between polyacrylic acid ( P A A ) and PVA, containing various numbers o f acetate links, as an example. Viscometry was selected as the simplest but an adequately informative method of following the process of complex-formation in aqueous solutions of PAA and PVC. In this method, the process of complex-formation is followed from the deviation in the relative viscosity, r/t~, of solutions of the polymer mixture from the additive value [7]. Viscosities were measured with an Ubbelohde viscometer. The viscometer parameters were selected so that the solvent time of flow should be greater than 100 see. This made it unnecessary to introduce any corrections into the experimental data. PAA was obtained [8] by the polymerization of the monomer in benzene in the presence of isopropyl alcohol as a molecular-mass regulator and with ABIN as initiator. The polymer was purified by precipitation from methanol into ethylacetate. The molecular mass of the PAA specimens was assessed by gel-permeation chromatography. MOLECULAR PROPBRTIF~ OF THE SPECIMENS

Specimen PAA-1.5 PAA-10

M x l 0 -4

PVA-7/9 PVA-1/19

8

0.6 7 1

[~],* dl/g 0"18 1"4

1.5 10

PVA-8/0

PVA-0.6/O

Acetate group concentration, mole

0 0 9 19

0"85 0"15 0"80 0"29

* Measurements for PAA in I M NaOHand for PVA,in water, Commercial samples of grade B and grade 18/11 (9 moleYo of acetate groups) PVA were used in the work. The PVA specimen with 19 moleYo of acetate groups was obtained by ethanolization [9]. The copolymer compositions were determined by back titration. The properties of the specimens and their designations are shown in the Table. Solutions of the polymer mixtures were obtained by mixing solutions of the individual components in the appropriate proportions. NaOH or NaC1 were introduced in some cases in order to suppress the polyelectrolytic effect in the system. Measurement of the intrinsic viscosity of polyelectrolytic systems by the method of iso-ionic dilution, which is uniquely correct, is extremely tedious. But since r/r,t varies in a manner proportional to [t/l, we made use of measurements of t/,,~. The dependence o f r/,.~ on the composition o f the mixture o f P A A - P V A solutions is shown in Figs. 1-4. In the main series o f experiments, the measurements were carried o u t at 25°C. The overall polymer concentration was selected to be equal to 0,5 wt. ~o

Complex-formation in aqueous solutions of mixtures of PAA and PVA

1861

since the general c h a r a c t e r o f the r h e o l o g i c a l b e h a v i o u r in the c o n c e n t r a t i o n range s t u d i e d (0.5-1 wt. ~ ) was f o u n d to be i n d e p e n d e n t o f the overall c o n c e n t r a t i o n (Fig. 1). I n all cases, the m a x i m u m on the r h e l - c o m p o s i t i o n curves was f o u n d at the s a m e c o m p o s i t i o n . T h e value o f the m a x i m u m m e r e l y increased with a n increase in c o n c e n t r a -

r~ret

2

1.5

I

I

40

I

80 PAA,wt.%

I

40

80 PAA,wt..%

FIG. 1 FIG. 2 FIo. 1. Dependence of the relative ~iscosity of aqueous solutions of mixtures of PVA-8/0 and PAA-10 on their composition for the following overall polymer concentrations: 1-0" 5; 2 - 0 . 7 5 and 3-1"05 wt.~o FIG. 2. Dependence of the relative viscosity of 0"5Yo solutions of mixtures of PVA and PAA on their composition. 1 - PVA-8/0-PAA-1.5, water, 25°C; 2 - PVA-8/0-PAA-10, water, 25°C; 2 " the same as 2, but at 80°C; 3-PVA-0.6/0--PAA-10, water, 25°C; Y - t h e same as 3, but at 80°C; 4-PVA-8/0--PAA-10, 25°C, 1 M NaOH and 5 - a s for 4, but with 1 M NaCI.

/~Pe[

4

2

2

1.5

I

40

I ....

80 PAA~wf.%

I

0.4

I

0.B c, wf.%

Fro. 3 FIG. 4 FIo. 3. Composition dependence of the relative viscosity of 0"5Yo aqueous solutions of mixtures of PVA or its copolymers witb PA.A at 250C. 1-PVA-8/0-PAA-10; 2-PVA-7/9-PAA-10; 3 PVA-1/19-PAA-10. FIG. 4. Dependence of the reduced viscosity of aqueous solutions of: 1 - P A A - 1 0 and 2 - a mixture of 25 w t . ~ of PAA-10 and 75 wt.Y. of PVA-8/0 on the overall polymer concentration, c, at 25°C.

1862

S . G. BEL'NIK~/ICH e t aL

Lion. The observed positive deviation from additivity in those cases when it occurred did not reach a maximum at a 1 : 1 composition. This fact is evidence of the formation of NPEC. It is also confirmed by sedimentation experiments in which only a single peak has been observed both in the case of solutions of homopolymers and also in their mixtures, which are characterized by positive deviation from additivity in the relationships between ~rel and composition. A comparison of the behaviour of a system (Fig. 2) involving the low-molecular specimen PAA-I'5 (curve 1) with that of a system with the high-molecular specimen PAA.-10 (curve 2) enables it to be concluded that the molecular mass of the PAA specimen should be higher than a certain critical value in order for NPEC to be folmed (positive deviation from additivity). By contrast, the molecular mass of the PVA specimen did not affect the process of complex-formation within the range of molecular mass studied (see Table) (Fig. 2, curves 2 and 3). A similar effect has also been observed previously in the case of other m ' E C [2]. The effect of the composition of PVA copolymer on the process of complex-formation is illustrated by the data shown in Fig. 3. Unfortunately, we did not have available copolymer specimens with different concentrations of acetate groups but with the same molecular mass. Because of this, a definite effect of molecular mass is also superimposed on the effect studied. The values of r/,el differ markedly. Nevertheless, the positions of the maxima on the curves remain unchanged within the range 0-19 moleyo of acetate groups, relative to the composition axis. The maxima differ only in their magnitude. We can thus state that, within the range studied, the copolymer composition does not affect the nature of the complex-formation in the system. If it is also taken into account that the acetate groups, randomly distributed along the PVA chain, cannot make contact selectively with the PAA links, the absence of any effect of their number on the process of complex-formation can be explained only by there being a small number of contacts (points ot regions) between the macromolecules that take part in the complex. An attempt to determine the hydrodynamic dimension of the complex did not meet with success since the quantity rhp/e (Fig. 4) increased as the solutions were diluted, showing that both in the complexes as in PAA, polyelectrolytic swelling is observed. When NaOH is added to the system, a reaction occurs between the alkali and PAA as a result of which the sodium salt of PAA (Na-PAA) is formed. The macromolecules of Na-PAA and PVA are found, because of the ionization of the substituted groups, to be incapable of a selective interaction that would be caused by interchain hydrogen bonds and complexes are not consequently formed (Fig. 2, curve 4). This fact, in addition to the effect of the molecular mass of the PAA specimens on complex-formation and the absence of any effect of the molecular mass of the PVA specimens, confirms that PAA macromolecules play the decisive role in the formation of NPEC. The decomposition of the complexes also occurs when NaC1 is added to the system since the low-molecular salt changes the ionic strength of the solution and suppresses the selective interactions between the PAA and the PVA macromolecules (Fig. 2, curve 5). It should be noted that, as distinct from NaOH, the introduction of NaCI

Complex-formation in aqueous solutions of mixtures of PAA and PVA

1863

leads to a marked reduction in the hydrodynamic dimensions of the macromolecules present in solution since the decisive role is played by the well known salting.out effect in this case. The effect of temperature on the process of complex-formation may be illustrated by the data in Fig. 2 (curves 2 and 2', and also 3 and 3'). An increase in temperature from 25 to 80°C only slightly affects the position of the maximum on the ~/rercomposition curves (a slight shift towards higher concentrations of PAA in the mixture, connected with a decrease in the strength of the selective interactions). The properties of the solutions change with temperature in opposite directions. Let us note in passing that, in the case of PAA solutions, an increase in temperature lowers the thermodynamic quality of the solvent (r/re1 decreases, other conditions remaining the same). In the case of PVA solutions, the opposite behaviour is observed, which also causes the curves to be "flattened out" in the region of high PVA concentrations. Let us attempt to put forward a model by means of which it would be possible to describe the structure of the NPEC. We shall write the total length (a measure of the apparent molecular mass) of all the macromolecules participating in the formation of the complex in the form: nL1 + nzL2, (1) where L1 and L2 are the contour lengths of the macromolecules of the first and second type participating in the complex and n and nz are the number of molecules of the first and second type. For each pair of polymers, there should clearly be a certain zcr that characterizes the maximum number of macromolecules of the second type that may be combined in the complex with macromolecules of the first type. Our further discussion will relate to z<~zcr. The intrinsic viscosity [t/] of solutions of polymer mixtures may be written in the form:

wI[ ]1

(2)

where [~l]aaais the additive value of the intrinsic viscosity and wl and w2 are the weight fractions of the macromolecules: L1

wx = L1 + zL----------2"

zL2

w2 = L1 + zL~

(3)

We have, according to Flory: I-T/]= 0 (h2) Zl2M- 1 = 0 ( LA) 3/2M- ~

(4)

Here 0 is Flory's constant, (h 2) is the mean-square distance between ends of a polymer chain and A is the magnitude of the Kuhn segment that characterizes the thermodynamic ~igidity of the chain. Let us consider possible versions of the macromolecular organization in the complex and the deviations in [~/] from [rl],aa connected with this organization. Version 1. The structure of the complex is similar to that of a block-copolymer (Fig. 5a). Let us assume for simplicity that n = 1. Along the length, L : , of the macromolecule, z macromolecules

1864

N. G. BEL'NIKEVICH et al.

are randomly, distributed, each with length L2. Thus zL2<~Lx. The characteristic chain rigidity in the mated regions is denoted by A*. Hence we have for the complex: (h2>k = (L x - zL 2)A~ + zL 2 A*

(5)

Consequently:

[~,,]=[~],w,.\

.t.,,. ~,a,.

1]

(6)

For the critical conditions zL2 =Lx, we obtain [t/],= [t/], wxA*/Ax

(7)

[,t]~= ['th w~ < [tt]a~

(8)

For the case AI =A*, we have

And finally, for A* > Ax, starting from a certain value of A,

[~ ]~ > ['t ].d~

(9)

b

if,

FIG. 5. Structural models of non-stoichiometric polyelectrolytie complexes: a - t h e block-copolymer structure; b - t h e comb-like structure; c - t h e star-like structure; d the randomly branched structure. Version 2. The structure of the complex is similar to that of a branched macromolecule (for simplicity, the thermodynamic rigidity of the chains is assumed to be unchanged by complex formation). The intrinsic viscosity of a branched macromolecule is related to tb.at of a linear macromolecule with the same molecular mass by the relationship [5]:

[r/]b,= [r/].,g (m)

(10)

where# (m)is the index of branching and m = 2 z + l is the total number of chain sections in the branched structure of the complex (Fig. 5). For a system of this type, the intrinsic viscosity may be written [10] as: [q]br= [r/h (1 + zL2]L 1)t/2 (11) Version 2.1. The macromolecular formation of the complex is similar to that of the comb-like maeromolecule with regularly positioned branches of the same length. In this case, [10]:

g(m)= 1

I +3L2/L1

+ mZ, ~(f-2~/z,,

,

(12)

Complex-formation in aqueous solutions of mixtures of PAA and PVA

1865

where f is the functionality of a branching node. For the case f= 3:

[,flo,=,,=

[q]l(1

zL2~X/2(1 -t-3L2/Lx) +-~x) (I+mL2/L,)

(13)

Calculation shows that, as z increases, the value of [V/]combdecreases. Version 2.2. In the case of branched macromolecule having a star-like structure [10] (Fig. 5c):

#(m),tat=( 3 m - 2)/m 2

(14)

and consequently [q ],ta, = [~/]1(1 + zL2/L 1)112(3 (2z+ 1 ) - 2) (2z+ 1)2

(15)

In this case, the value of [~/],t,r also decreases as z increases. Version 2.3. This corresponds to the case of a randomly branched macromolecule (Fig. 5d). For trifunctional branching nodes, the branching parameter may be written in the form: ff (m)rbm= (4m/9 +(1 + m]7)112)- 1/2

(]6)"

Consequently: [r/]rbm= [~/]t (1 + zL 2/1. z)x/2/((Sz+ 1)/9 + 1 + (2z+ 1)/7) I/2

(17)

In the limit for z>>l, we obtain: [r/]rbm'~(9L 2/8L1) 112 [r/]z

(18)

For a certain value of the ratio L2/Lt, the value of [rl],b. can be grealer than [q]aaa. It should be noted in passing that, for z > zc,, some of the macromoleeules of the second type exist in the free state in the solution. This must be taken into account in determining w2. ZkcrL2

w~= w2 -- w , Lt

(19)

These macromolecules make their own contribution to the value of [r/l, which is taken into account in equation (2). Thus a positive deviation from additivity when summing the intrinsic viscosities of components in the case of complex-formation occurs with the block-copolymer structure when A* >>Ax or with the randomly branched macromolecule. But if it ~s additionally taken into account that the radius of inertia of NPEC decreases with an increase in z, the most probable structure of NPEC becomes the branched macromolecule with trifunctional branching nodes.

The authors wish to thank A. Ya. Sorokin for making the specimens of PVA-1/19 available and V. M. Belayev for caxrying out the sedimentation experiments. Translated by G. F. MODLEN REFERENCES 1. A. B. ZEZIN and V. A. KABANOV, Uspekhi khimii 51: 1447, 1982 2. A. D. ANTIPINA, V. Yu. BARANOVSKII, L M. PAPISOV and V. A. KABANOV, Vysokotool. soyed. A14: 941, 1972 (Translated in Polymer Sci. U.S.S.R. 14: 4, 1047, 1972) 3. V. B. ROGACHEVA, S. V. RYZHIKOV, A. B. ZEZIN and V. A. KABANOV, Vysokomol. soyed. A26: 1674, 1984 (Translated in Polymer Sci. U.S.S.R. 26: 8, 1872, 1984) 4. Ye. A. BEKTUROV and L. A. BIMENDINA, Interpolimernyye kompleksy (Interpolymeric Complexes). 264 pp., Alma-Ata, 1977

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Ye. A. Sn,mwcH et al.

5. M. M. KUKHARCHIK and N. K. BARAMBOIM, Vysokomol. soyed. 19: 1358, 1967 (Translated in Polymer Sci. U.S.S.R. 19: 6, 1562, 1967) 6. G. R. WILLIAMSON and B. WRIGHT, J. Polymer Sci. A3: 3885, 1965 7. V. P. BUDTOV and V. V. KONSETOV, Teplomassoperenos v polimerizatsionnykh protsessakh (Heat and Mass Transfer in Polymerization Processes). 286 pp., Leningrad, 1983 8. T. L. KARPINSKAYA and Ye. M. LUKINA, Plast-massy, 6, 14, 1980 9. V. A. BALANDINA, D. B. GURVICH and M. S. KLESHCHEVA, Analiz polimerizatsionnykh plastmass. Prakticheskoye rukovodstvo (Analysis of Polymerization Plastics. Practical Handbook). 512 pp., Leningrad, 1967 10. S. R. RAFIKOV, Yu. B. MONAKOV and V. P. BUDTOV, Vvedeniye v fizikokhimiyu rastvoroy polimelov, G1. 7 (Introduction to the Physical Chemistry of Polymer Solutions. Chapter 7), Moscow, 1978

Polymer Science U.S.S.R. Vol. 31, No. 8, pp. 1866-1874, 1989 Printed in Polnad

0032-3950189 $10.00 + .00 O 1990 Pergamon Press plc

,ON THE NATURE OF SPONTANEOUS ELONGATION DURING THE IRRADIATION OF POLYMERS WITH PRIOR STRETCHING IN ADSORPTION-ACTIVE MEDIA* yR. A. SINEVICH,A. M. PRAZDNICHNYLV. S. TIKHO~ROV and N. F. BAKEYEV Karpov Physicochemical Research Institute (Received 5 February 1988)

A study has been made of the nature of the spontaneous extension effect occurring during fast electron irradiation of polymers subjected to prior stretching in adsorption-active media. This effect is associated with radiation heating of microporous polymer samples. Manifestation of the effect in amorphous PETP is necessarily related to the presence of crazes with a well developed microfibrillar structure. It was found that the spontaneous extension effect is due to crystallization of partially oriented material in transitional regions relating the oriented material of microfibrils inside crazes to unstrained polymer in interspaces between crazes.

MICROPOROUS materials formed via the stretching o f polymers in adsorption-active media (AAMs) are structurally rather unstable: Already on removal of the load there is a significant degree of linear shrinkage of moist samples which, in the case o f glassy polymers, markedly exceeds the shrinkage o f samples that have been stretched in air. The change in dimensions is still greater during the drying of samples in the free state: after volatilization of the A A M from micropores the shrinkage may be as much as ?

* V~sokomol. soyed. A31-"No. 8, 1697-1703, 1989.