3693 JOCR:-AL OF POLY:\IER SCIE:-CE, Polymer Chemistry Edition YOL. 13. 1-HI-1-156 iIQ75l Starch Xanthate-Polyethylenimine Reaction Mechanisms :'If. E. CARB, B. T. HOFRElTER, and C. H.. H.USSELL, Northern Re(liollal Research Laboratory, Auricultural Research Service, C.S. Department of Ayriculture. Peoria, Illinois 6'16'04- Synopsis Thl' C'hemiC'al nature of starch xanthate (SX)-polyethylenimine (PEl) reaction produC'ts ha.~ been studied berause of their effertiveness as wet-end additives for im­ prllving strength properties of paper. :\lodel rompounds, in ronjunction with ultra­ vitllct, infrared, and chemical analyses, served to elucidate SX-PEl reaction mecha­ nisms. Aqueous solutions of ~X (degree:s of :sub:;titution O.l-D.;,) were titrated with PEl at pI! :.-i (2,i-:lQoC) to form SX-PEl !locrulent precipitate:s that were determined til hl' polyelectrolyte complexes. However. when :solutions of SX-PEl were kept at pH Ill-I:!. produc·ts were formed that induded dithiocarbamic acid salts in major quantities, PEl thiourea.-, and minor quantities of O-:starch PEl thionrarbamate. Acid precipita­ tion of thesl' ~X-PEI polymeriC' reaction products from their alkaline solutions, which ('Ilntained residual xanthate and PEl. also yielded polyelectrolyte complexe:;. :\lodel ,.'·-tems suggest th:lt PEl thiurum disulfide and starch xanthide, pos:;ible products of air lOxidal iOII, ('ould he present in minor amount:; and would react rapidly with PEl to yield thi'l\lreas and thioncarbamates, respectively. Apparently, mixtures of xanthate and alnin!' gave (1) dithioearbamic aeid salts from both xanthate groups and CS, (decom­ positilln from xanthate), (2) thioureas from both dithioearbamic aeid salts and thiuram eli,ulfide, and (;l) thionearbamates, principally from xanthate a:s opposed to xanthide. INTRODUCTION Sodium :<tarch di thiocarbonat p (:<t arch xanthatp. SX), oxidatively cross­ linkpd in p:lJ){'rmakill~ fumi:<hl':<, improVC':< wpt and dr~' strpngth of paper. l III {'ontilluin~ ('ffort:< to improvp til!' l'ffl'ctivpnpss of SX as a wpt-end paper­ :-trl'll~thpnill~ additiVC', such rationir poJynH'r:< as E:ynwnp ;j;ji and poJy­ I'thyh'nimiIH' (PEl), whieh han :-itf'''; for ioni{' and covalPnt bonding of xanthatp [-OC(8)S- j, have' 1J('('n iIlVP:<ti~atpd as altprnativp crosslinking agpnt,.;,u Our lat(':<t \\'ork. whi('h inyolyp,; rpartions that occur in aqueous :-o!utions of SX with PEl. wa:< madp to facilitate application of SX-PEl products in pappr and studip,; of :<imilar p()!ydectroJ~,tic systpms. PEl. a po!yaminp which eOIltain:< primar~·. :-pcondary, and tertiary amine ~roup:< in thp ratio of I;:.?; i.4'prpviousJy has bpPIl reactpd with polymers of oppo,;itp chargp ~o forn~ polyplectrt'llyte complexes,:> For example, mercury ion in part:; ppr biliioIl.rol1,cpntration have bpPIl ,;ubstantially removed from wa:<t('watpr by sPqu('Ilti~1 n.qqitions of PEl and SX, forming watcr-insoluble po!yf'1pctro!ytp eomp]pxp,;.6 Ho\\,pver. thpsc complexes per se were not 1441 C' 19i;j hy John Wiley & :-;on~, Inc. 1-i1:2 CABB. 1I0FHEITEH. A:\D BeSSELL analyticall~' charactprizrd, InnonpolynlPric systpms. reactions of primar~' and "t'('ondar~' amilH'" \\'ith xanthut{' "alts in aqueous alkaliIlP "olution" can yidcl thioncarbamat{',.;! H{'portpdly, aqueous solutions of SX and PEl a~('cl at pH 1O-1:.! and room t{'mpprature have yielded thionearbamatp [-0('(:-;):\<, 1intPrpolyn1l'r::,,3 Howen:r, others have stated that aqueous alkalilll' mixturp;; of edlulo,.;(' xanthatp and PElon aging yielded dithio­ carbamic' acid salb [):\C(S)S-l and thioureas [)XC(S):,\(1of PEl but no thilllll'arhamat{' producl.' Thc' PEl dithiocarbamic groups were beIipvcd to form from CS~ of dc'composed xanthate, Reportedly, air oxidation of nOllp,,],I'IlH'ri~ dithiorarbamic aci(-alts can yield:thiuram disulfides [):\C­ (~)~~(:-;)(':\(l aIllI thiourc'a;;,9 TllP thiourpas may bp fornlPd readiI~' by rc'a('lion of primary and ,,('condar~' aminp;; with thiuram disulfides. Anal­ og'l\l" I 0 air oxidution of dithiocarhamic group;;, air oxidation of xanthatps can .\'it,ld xanthidp,.; [-OC(S)S~(S)CO-l which readily react \\'ith primary alld ,,('c'ondar~' amiIH's to yidd thioncarbamates. ~('\'('ral reaction products inrluding polyelectrolytf' complexes \\wp fornH'd in aqueous solution;; of SX \\'ith PEl at pH ranging from 5 to 12. \\'ith tIll' aid of modd system;;, tl1("se products wpre charactprized by ultra­ \"ioll'l. infrarc'd. and c1l<'mical analy;;ps. All reactions \\"ere at :25-:30°C. RESULTS AND DISCUSSION SX-PEI Polyelectrolyte Complex \\'llI'n a 1Sc aqu('ou" "olution of PEl GOO was slowly admixpd with a O,:!r; aqu('ou;; ;;oIution of SX havinf!; a dpgT('{' of substitution (DS) of 0.15, alld \dll'1I pH \\'a" maintailwd at 7,0, a flocculent precipitate \\'as formrd aI a dr.\'-\\'(,ight ratio of 0.1-1;) part PEI/1.0 part SX. Alternatively, wlwn "oIUlioll" of tIl<' alkalinl' rC'actant;; WPr{' combill<'d at the sanw concentra­ til In" and ratio". but pH wa" ;;lowly 100\'('rc,d, precipitation occurred at pH i. TIll' frc':-:h pn'C'ipitate;;. obtailwd in U;-)% yields (SX-PEI addition basis), had ;;ullllr (·L-IS;) and nitrog('n (:3.HSc) content;; that \\we about theory for a produC't c(,ntaining 0.1-1'-) part PEl 1.0 part of DS O.L':> SX (theory; 4.8% S. -!.1C;( :\). WI1('n tIll' fn'"h undri{'d prpcipitate:-; were treated with acid (pH Li) t.o deccJlnpo;;(' xantllatl' group". CS~ \\'as recovered 10 in amounts corn'"pondiug to origiual xauthat(· cout('ut;;. PEl dithiocarbamic acid salt,.;, !l0;;;;iblc' compon('ut,.; iu tIl<' SX-PEI precipitates, abo would release C~: at pH L'). Ho\\'('v('r at pH 11. thC' fn'sh undried precipitates readily "ululJiliz('d and contailll'd U:3-!l7SO of the theoretical amounts of xanthate, a;; d('(prmiIH'd by ultra\'iol('( analysis (t-~~~ = 30;'), E 17,500). These data :::ho\\'ed that tIll' [n'sh undried precipitates were SX-PEI polyclectro­ Iyt(, complex('s. TIl<' ('ff('cts of pH, xanthate DS, and concentration on the amount of PEl requin'd to form these complexes, and analytical data are ginn iu Table 1. STAHCII XA \TfIATE-/,OI.YETIIYLE\I\J/\E IH:l TABLE I I'rrp:lr:ltilln :lnd Analy~p." of :-'tan·h X:lnt hate (~,x )-!'olyet liyll'niminr (PEl) l'ol\'p]petrlllyte Complexe~" Amoullt of PEl rl'ljuired to pre('ipitate Analy~es of ;-;'x-PEl l'OInplpx. preeipitated eomplexh ])pgn'(' .,f Coneell­ part~!] 00 part~ s,x ~ul"t it ut illll tration, Yield, :-'ulfur, Xitrogell, 1):-' ,.. e­ c-' c-' ,I pH .i pI! i /( ,I I 0.11 O. J() i ,I O. 1,-, O.OJ 0.1.-, 0,0:; J.i ..i O. 1.-. 0.10 \1.0 14.;' \14 .0 4.0' 3.H O. 1.-, O.:?O 14 ..i o.::! O. J() l::?O W.O f).i.;i S.i 4.0 " :\qlll'OIi' PEL (I (';) wa" slowly added to aqueou" SX, with "tirring, until a prl'­ ,·ipitatt· wa~ fOrIUl"/. Sulfur ('ontent was determined withiu 1 hr after precipitatiou. h 1'1I1~'l'll'('trlllyte ('omplexes formed at pI! i. Yield = wt of preeipitate -;- wt (;-;X + PEli X 100. e Expl'riment wa" not made. d :'I iiik.\', uo prpl'ipitate. l'/tra\'i"lpt analyses of agp<! ~X-PEI ('omplpxP" illdicatt'd that rpaetioll" h:ld lI(·('lIrfl·d "imilar to tho"p ill aqupou" SX-PEI ;.;olutioll" at pH 10-1:2. Alkaline SX-PEI Solutions :\11 aqlll'lIl1'; "(,]utioll "f SX alld PEl at pH 11 was prqlar('(] that eOIl­ taill!'d :-:X of DS 0.:2:2 at ,jS~ C'"l('t'lltratioll alld pntJUgh PEl noo to gin a ratill "f al1lillP to xallthatp group" of:2: 1. conditiolls that WPrP prt'\'iou"ly r('pllrt('(P to yi('ld ··"tarch polyl'thykllimino thiour,thant·." all O-stareh PEl thiolll'arhamatt·. Oil al!illg. u/tra\'ioll't ab"orptioll of t.hi" alkalillP :-:X-l'EI ""Iutio!l gradually "hift<'d from it" xallthatp maximum at :30;j IIIll tCI :mo IIIll (1-:2 da~',,). :2\1:2 11m (;j day,,). and filially :2S\lllm (:2S dny::;) \\'ith t'oIlCUrr('lIt formati"l1 of a \\'('akpr 1I01l"hifting abmrptioll at ::WO Ilnl. Tlwfl' \\'a" poorly dplillt'd ah"orpt iOIl in thc' rpgion of :2:{;-)-:24;j nn1. \Vhpn a('id-trt'atpd (pH 1..-,), till' ag('d (.-,-:2,\ day,,) mixture' exhihitpd an ab"orptioll I)('ak at :2:{!I 11m hut 1I0tH' at :2(iO :\Ild :2,\\1 11m. :\t pH i-I:!, ab"orption b~' til!' :H'id-trpatpd Illixtllfl' "hiftpd ff(l1l1 :2:{\1 Ilm to :2:37 111l1. Ultraviol(·t ~I)('('tra of tilt' fl't'"h and :2,\-da~'-old Illixtuf(' hC'fOf(' and aftt:'f acid tr<'atment art· rc'produ("('d ill Figur(' 1. .-\I>"orption at :23:>-:24.'> nm is partially ob­ ,,('urt·d iJ~' m'('rlappillg: ab"orption" of alkali at lower wavl'!el1gths. SX ha" a \\'('ak ah"orptioll at :.?:.?i 11m. SX-PEI prodUt"l" in alkalillt' "olutiol1 wC'rp prC'cipitatC'd in C'thanol. iso­ !alt·d. and rpdi".,;olv(·d at pH 1:2. The ultraviolet spectra of these redi~­ sol\'('d prt·('ipitatt·" \\,pre' ~imilur to tho:-:p of tIlt' solutions from which they \n'rp prc'l·ipitatPd. Dltravioll't spl'ctra of tIlt' SX-PEI solutions in Figure 1 \\'('f(' typical of :-:p('etra that contained initial xanthate DS of 0.1-0.5, SX 1444 CARR. HOFRElTER. A:\D RUSSELL 0.0,-------------------, --------- 02~ 2 .--- / ... --- r ~ 04f- I;/;/ I; ~ __ /I ' " /I ~ 4 .I' " /I 0 6f.- / , '/ '" , ,.... / ='" ~ 0 B - i .' -5 = I ' ..