Oct., 1961
POLY-(VINYLBENZYLTRIMETHYLAMMONIUM)
POLY-(SmRENESULFOS.~TE!
1765
POLYCATION-POLYANIONCOMPLEXES : PREI’AI-UTION A S D PROPElRTIES OF POLY-(VINYLBEn’ZYLTltIJIETIIYLA~~~~OSIUbl) POLY- (STYRENESULFONATE) BY ALANS. MICHAELS AND RICHARD G. MIEKKA l)epartwnmi of Chemical Engineering, Massachusetts Institute of Technology, Cambridge 39, Massachusetts Received June 90, 1961
High molecular weight poly-(vinylbenzyltrimethylammonium chloride) co-reacts in dilute (O.ti g./dl.) of the polymers are mixsed, an extremely thin (m.200 A.) complex film forms a t the two-solution interface, which completely blocks further pokymer interaction. These films can be isolated; they show very high diffusivity toward simple electrolytes (NaCI), but lower diffusivit toward larger ionic species (methylene blue chloride). Fairly fluid solutions, containing rather high concentrations (10 g J J . 1 of both polymers, can be prepared in a ternary solvent system comprising ca. 205% acetone, 20.y0 NaBr, and 60$; water. Dilution of these mixtures with water, or evaporation of the acetone, results in gelation. By suitable washing i;echniques, amber, glassy solids, free of extraneous electrolyte, are obtained. By this route, stshle complexes containing excess polycation or polyanion, as well as the neutral polysalt, can be pre ared. The non-stoichiometric complexes appear to undergo structural rearrangement by a mechanism of internal ionic [ond transfer when swelled in aqueous acetone solutions, or when dried. The latter also behave m cation or anion exchange resins; the neutral polysalt selectively sorbs salt from aqueous electrolyte solutions. Mechanisms of polyion interaction, and the probable structures of the complexes, art: discussed in light of the experimental findings.
Introduction The precipit.ation reactions occurring between oppositely-charged linear synthetic polyelectrolytes in solutioa, and the properties of the precipitates are of interest becawe of their similarities to biological ~ y s t ’ e m s , ion ~ , ~ .exclusion ~ resins,4 and ion exchange resins and membranes. Precipitation is due to stroing electrostatic attraction between oppositely-charged macromolecules which causes them to be d.rawn together and react ionically, giving off their associated counter-ions as free The precipitates frequently can be dissolved, or their formation prevented, by the addition of suf‘ficient amounts of microionic salts (e.g., NaC1) to suppress thr: clectrostatic fields of the macromolecules. Wheri sufficiently concentrated solutions of oppositely-charged, strongly ionized polyelectrolytes are mixed, the precipitates sometimes take the form of t1ii.n continuous films which form a t the interface between the two solutions and completely block further interpolymer reaction. Dilute solution interactions between oppositelycharged polyelectrolytes have been st,udied by a number of investigators.1~2~6.6~s~9~i0 A study of the precipitation of pectic acid by polyethylene imine, together with an excellent review of much of the previous literature, has been given by Deuel, at aL6 They found t h a t precipitation occurred only in a narrow range of relative concentrations of these D. G . Dervichian. Discussion8 Faraday Soc., 18, 231 (1954). (2) H. Dsuel. .1. L3olins and A. Dengler, Helu. Chink. .4cla, 36, 1671 (1)
(1953). (3) A. Katchalsky. Endeaoour, 12, 90 (1953). ( 4 ) M. J. H a t c h , J. -4.Dillon and H. B. Smith, Ind. Bng. Chem., 49, 1812 (1957). (5) R. M. F u o and ~ 11. Sadek. Science, 110, 552 (1949). (6) E. R. Kruyt, Ed., “Colloid Science,” Elsevier Publishing Co., Inc., New York. N. Y., 1949, Vol. 11, Ch. 10. (7) H. Terayama, J. Polymer Sei., 8, 243 (1952). (8) A. Kossel, Z. phvsiol. Chem.. l a , 176 (1896). (9) R. G. Miekka, “Properties of Mixed Synthetic Polyelectrolytes,” S.& Thesis. ‘I.Chem. Ene.. 31. I. T., 1958. (IO) H. Morawets and W.L. Hughes, J. P h y s . Chsm.. 66, 64 (1952).
two weakly ionic polyelectrolytes. At the maximum precipitation point, the polyacid and polybase were quantitatively reacted, and 110 uiireacted polyelectrolyte could be found in the supernatant liquid. Electron microscope studies indicated that>the precipitates formed a t this optimum reacting ratio had a cross-linked structure. Fuoss and Sadeks investigated the stoichioii?etry of reactions occurring between 0.018 ,V polyvinyl-Nbutylpyridinium bromide aiid approximately 0.005 N sodium polystyrenesulfonate i n mixtures containing excess cationic polymer. They found a considerable variation in the weight of precipitate obtained (1.30-2.40 mg. of precipitate per cc. of sulfonate polymer solution), and the percentage of the total bromide ion trapped in the precipitate (5-10%), depending on the relativc amounts and order of addition of the polyelectrolyte solutions. Although tfie r c d t b reported here indicate more nearly equivalent proportion betwccn a pair of polyelectrolytes with Firnilar structures (at higher dilutions), we too have found considcrable deviations from complete eyuivalencc at polyelectrolyte concentrations above about 0.005 S. which we have attributed to the beginnings of in1 erf:icial film forming tendencies. The present study was undertnlw~t o determine the interaction characteristics of strongly ionized, oppositely-charged polyelectrolytes oi high charge density, and some of the properties of the reaction products (polysalts). The two polymers used throughout the study were poly-(sodium styrenesulfonate), XaSS, an anionic poiyelectrolyte with a molecular weight of 760,000, and poly-(vinylbenzyltriniethylammonium chloridc’l. T‘BTAC, a cationic polyclec%rolyte with a niolt1cular weight of about 300,000. Both polymers were furnished by the Dow Chemical Compaiiy of Llidland, Michigan. Prelirninarv inveqtigations of thc viscometric behavior of the individual polyelcctroiyte.; i n dilute
A0
t
2 , using a modified Ostwald capillary viscometer at 25". The polymers reacted under three different sets of conditions, each resulting in polysalts with clistiiictly different properties : (1) interaction bet,weeii dilute (O.G g./dl.) of the polyqers were mixed, an est>remely thin (ca. 200 A.) film formed at the two solution interfaces which completely blocked further polynier interaction; and (3) polysalts containing widely varying relative amounts of the two polymers were prepared hy precipitation from a ternary solvent syst,cm (SaRr-acetone-water) in which both polymerr could be dissolved Tvithout interacting. Experimental
-
50
40
c:. , e F
30
fi0
50
40 i
-> F
30
0
k
k
0.04 0.06 0.08 0.10 c, g./100 ml. Fig. 8.--ltediiced specific viscosity z'ersus polyelectrolytr concentration for NadS in: x, pure water; 0 , 0.001 3.1 NaBr; A , 0.01 .If S a R r ; and 0,0.1 3f NaBr. 0
0.02
aqueous solutions were made by Smith." He obtained thf, plot,s of reduced specific viscosity v8. polyelectrolytc c~oncentrationshoiyn in Figs. 1 and i 1 I ) N. I I . S i r i i t l i , "Viscometriu Study of Polyelectrolytes in Solution," Y. If. Thesis, Cliem. Kng. 31. I. T., 1959.
Purification of Polyelectrolytes. Extraneous microions were removed from t h r polymers by adding a demineralizing resin (a mixt,iire of cation excliangr resin in the hytirogm form and anion eschange resiii in t,hc hyrlrosidc form) to nqiieous solutions coiitaining :Mvct)y iwigiit of the polymers. .lftcr the pol>,mer solutions h:d bwn caiitacted with tlir rcsin for about 11' Iitriirs, thcy were filtered tliroiigh :t fritted glass funncl t o reniove the rrsin :uid ail)- contamiii:tnt particles which might bc present. Tlrc solutions w r e dried after being passed over appropriate ion oscliangc~rrsiiis to arsiire that the ticaircd coiintrr-ions wrrprrscnt on the polyelectrolytes. Equivalent Weight Determinations. The ionic eqiiivnlent wclights of the polynicw \yere tletermind by stand:trd haec titrations of SaSP after it had bren ion cscharigetl into the hytlrogcn form, and argentometric titrations of t h e chloritlr conntwions of VRTAC. The chloritf~titrntion endpoints were drtermined potentiometrically using a Beckmsn pH mctcr with hydroyrn and silver \vir(, elcrtrodts. The soliltions wwe buffcrrtl to pN 1to w e c o n r t m t hydrogen c~lrc.trodr~ potential during t h r teit ions. T ~ equivalent P weight of SaSS MYIS found to lx: 23-I =t 8, l 2 n-hilc the v d ~ i c for \-ET:lC varied from 2% =t 10 to 264 =t 10, drprntiing oil thv h t c h uscd. Th(' vnrinriw in t-quivnl(,nt \wight w:ts iwlievcti to reeiilt from t1egr:tdatiori of some of thc ( ~ I I : I ~ I T wiry groups, probably by 1)actwiit.l att:ieli i n solution. Dilute Solution Interactions txiiiing varying rrhtive amoiints twre made 111) from tiiliite (
