ISTRODL-CTIOS
In a previous paper of this series ( 6 ) mention w i s made of a method vhich had been devised for the quantitative fractionation of heat-polymerized non-conjugated vegetable oils. -Ifen- of the data ahstractecl from the present work were given in this previous paper, and were used for the purpose of testing the adequacy of the polymerization mechanisni advanced by the author. It is the purpose of the present paper ( I ) to give a general account of the polymerfractionation technique developed and t o attempt the theoretical ba selectivity, ( 2 ) t o give a detailed account of the specific procedure used in the fractionation of heat-polymerized linseed and soybean oils a t various stages of the reaction, including that of the final stage of gelation, ( 3 ) t o present the esperimental data ohtsined, and ( 4 ) to interpret the data not only from the Tien-point of general polymerization theory and polymer distribution, hut more specifically as a means of testing their correspondence to some of the postulates of the author's theory. I n contrast t o the extensive work n-hich has been clone on polymer fractionation of other systems, very little has heretofore lee11 attempted on the heatpolymerized drying oils. Norre11 (26) in 1915 reported a fractionation on heat-bodied linseed oil iising acetone. Only tTvo fractions were obtained, an acetone-soluble one consisting essentially of the remaining monomers :ind an acetone-insoliible one conskting principally of a mixture of all the polymers xi-hirh had formed. The acetone procedure has since been used by Elotl m d JIacli ( l G ) , Behar (4) 3IcQuillen and Koodn-ard ( 2 5 ) , and more recently 11y Privet t et al. (29). Their respective results are subject to the same inherent limitation, the reason for n-hich will he indicated later in this paper. Solvent-mixture procetlures have a150 been reported (15,20,30) but specific polymer fractionations have not heen claimed, and their purpose i. either to fractionate the iinpolymerized oil or t o separate the lon-er unsatiirated monomers from the polymers as a group in the bodied oils. More recently there was announced a separation scheme involving liquid propane (21). The details of the process so far reported are concerned u-ith the separation of the saturated and lon-er unsaturated monomers from the more highly unsaturated monomers in unbodied fish !
1 Presented in part before the Division of Paint, T'arnish, and Plastics Chemistry a t the 105th Meeting of the American Chemical Society, n-hich was held in S e v I-ork City, September, 1911. 2 Present address: Gothani Ink ck Color Company. Long Island City, Ken. l-ork. 613
x
614
I. 31. BERSSTEIS
nnd vegetable oilz, r'ithcr than TI ith the poq-ibility 01 specific fractionation of *polymers. The chrbmotographic adsorption technique has been successfully ; u p & e d t o the ffWtioxpiion of unbodied wgetalile oils by Walker ( 3 5 ) , h i t n o E *. ti'ork has'been reported on it- applicability to the heat-polymerized oils. Mention must, of coiirse, al-o be nxide of the molecular .till procedure ah developed 1)y Hickman (19) and used by Morse ( 2 T ) , I3radley (9), and Katernian (Xi in effrcting tlie fractionation of polymers. Thi- procedure ha?, lioivever, two inherent difficulties: (1) that it is not :ipplicnble to the heat-polymcrized glycciide vegetable drying oil; c x e p t t o remove the ,atur,ited and lon- u n w t wated monomem remaining, and ( 2 ) that even n-itli the methyl ester.; it i.; questionable, a t the temperature of di+tillation. Tvhetlier further polymerization of the residue does not occur after the dimers have been distilled off. -4q n-ill be ihown later in this paper, the higher polymers after being stripped from tlieir adsorbed monomers and l o w r polymer, are particularly sensitive to osidation and /or polymerization and tend t o form gel- at room temperature even where precautions such as an inert atmospheie are observed in order t o prevent access of air to the system. ~
I. FRACTIOSATIOS BY SELECTIVE SOLL-BILITT I S T H E HOJIOLOGOUS SERIES OF S O R J I I L JIOSOHTDRIC .iLCOHOLS
A . General discussion The fractionation method Jvhich is thc txx of the prescnt paper differs from those previously nientioricd in t1i:it it en:hles one not only to separate the nionomers from the polymers present in tlie lie:it-l?ol~-nierizednon-conjugated vegetable oils, but in addition to sep:ir:ite the polymer portion into a large number of fractions of varying polymcric sizes, thc n ~ a n b e rof such fractions present depending on the extent oi' the polymerization (ii . This method is b cl on an obs.crvation by tlie author that, linseed :md soyhean oili in the unpolynierizetl state, Irhilc completely soluble in 11-propyl a1coli01 (although practicnlly insolu?)lc in nicthyl mtl ethyl alcohols), become progressively insoluble percentagewise in this solwnt :is the heat-polymerizatiori progresses. S o t only is this true for ti-propyl alcohol, but it is likewise successively true for the othrr higher members of the homologous series of thr liquid normal aliphatic saturated monohydric alcohols up to and including ?i-clodecyl :~lcohol,the highest liquid member of the serics at room temperature. At any one stage in the polymerization of the above oils complete solubilit'y can he ohtained n-ith some one of the ascending members of the homologous series of alcohols. A s soon, however, ns the polymerization exweds the particular stage in question, partial insolubility in that, alcohol occurs, and it is necessary to go t o t,he nest higher number of the series t o achieve complete solubility again. The limiting point, in the series is when the polymerization reaches the partial insolubility stage n-ith wdodecyl alcohol. complete solubility a t this critical point may, hoivewr, lie achieved by the use of petroleum ether as the solvent. Petroleum ether, essentially hexane, continues ns a complete solvent for all of tlic s;lthsequent Ftage3 of pol\-merization up t o ])ut preceding that of gelnt ion, i\here
615
POLTJILR FR IC TIOh-.ITIOS O F HEAT-POLTXERIZED OILS
partial insohibility again results through the formation of insoluble, infusible. cross-linked polymers. Tables 1 and 2 illustrate the relationship bet'n-een the polymerization time of linseed and soybean oils and complete solubility in menihers of the above homologous series of normal monohydric alcohols. -4s a corollary t o these relationships, the members of the ascending series of normal monohydric alcohols are complete solvents for all of the heat-polymerized T.4BLE 1 Re1 a i i o n s h i p beitreen polymerimtioiz lim nntl complete solubility in normal monohydric nlcohols ( a t W C ' . ) of' hcut-polymerized linseed oil* E O t X S AT POLY.\IERIZ.\IION TEYPERAILRE I 30i'C.j
)I-PROPYL ALCOHOL
11-BUTYL .x.ciiwL
__________
0 1
2 4
6
I
s 0 10 -
R-.4MTL .ALCOIIOL
- ~ _ _ ~
s-
n-OCTTL .\LCOHOL
1Z-DECYL ALCOLOL
-
~
~
12-DODECPL ALCOHUL
-
~~
_
_
_
. ., ..... y . . . . . ., . . , , . , , . . . . y __ ............................ y ...................................... y ................... ................y ................... ................................... ........................................ ...... ............................................................ .
~
'*
11-HEXYL .ILCOHOL
D o t t c d line = ~ a i i g eof partial solubility. Scilitl line = m n p c of complctc solubilit~-.
5 5 1'7 14 16
. . . . . . . . . . . . . . . . . .y .......................... . , y ..................................... y ............................................... .. .................
-------
y
-__
Dotted line = raiige of partial soluLilitJ-. Solid line = range of coniplete soluhility.
oil sample:, previou. to the alcohol in wliich partial solubility occurs. Petroleum ether, on the other hand, is a complete solvent for all of the oil samples, from the unbodied stage t o that immediately preceding gelation. B . Silectiue polyincr solitbility
iri
homologous scries of izormal ~iioiioliydricalcohols
It may be inferred from tables 1 and 2 that the members of the homologous serie.\ possess a selective solvency for the oil polymers such that, as the polymers
G1G
I. 11. BERSSTEIS
gron- in size, the>- eslnihit progreshively decreasing soluhility in the successively lower memhers of the alcohol ,;cries. Thus, a,iliiy i\ con.istcnt in :ill 01 rhc polarity expressions g n en for the iiornial alcohol.. it ia not .r) c\idcni for hexane in relation t o t h o s for the alcohols. For hexane the dielectric. con*tant iperific dielectric constant, and the specific polarization all indicate a lowering of polarity consistelit with its increased solvency propertj- for the oil polymer \\--tern9 under conderation, whereas the refractive index indicates an incr.ea,e in polarity. The reason for this disrrepancy is not apparent. TXBLE 5 C o m p a m t i r c polaritics o j hexairc arid cycloiitxnric
E . l'ola,.l'fg 'j
01, c o , ~ - c c i r ! ~ j ~ i yt oi ir(( g( faLlc, oilcc tnkcn into nrcount. It ha' Ixwi inclicsted hy 1,nngniuir ( 2 3 ) 11i:it the polarity of :L fatty acid of the C ' L 3 group i y dependent on iis clcgrcc of iins:itnratioii. Stcpincnko. _lgranat;,and Soviko-$-a (34) h a w tleierniincti tlic dipolc iiioniciit? of tlirrr of the C13fatty acids in rliosm e and linvc +hon-n t h t the dipole nion~c1~; inrrcuses from 1.63 in stearic l o 1. T I in linoli(3 arid. 'I'hesC :~ntliorsalso rcported the values for the dipole. moments of tristearin antl triolclin :IS 2.93 m d 3.0(i, re+;pcclirely. ('aicln-ell antl Payne (12'\ inr-cstigatcd the tlipolc moments of unbodied linseed and perilla oils in tlic absence of solvt~its;\vhilc tlic>irr - d i i w of 2.100 and 2.003, rcs;prctivc.l!-, are generally of a some\\-hat lon-cr orcler of inagnitude t hnii those of the piel-ioiis authors;, they lilmr-iac indicatc an owr-nll higher polnrity n-ith incrcwing iinsitui'ation. difficulty prescnis itself :it this point lvith respect to the polarity--oliit,ility relationships h e t w e e n thc CIS fatty acids :ind their triglycerides, n-hich merits soinc discnssion. It is apparcnt from the a b o w dipole-rnomcnt data that tho fatty acids havt :xi npparcntly 1on.c~polarity than do the corresponding triglyccridcs ani1 yct. as is ~\-cllknown. the fatty acids are readily soluble ei-en in methyl alcohol. n-hcrcas the triglyceride mononiers requirc at least n-propyl alcohol for bolnbility. If one takes, liowver, the corresponding inolecular weights of thc fatty :?cirls :incl their triglyceride monomers into acco11nt~and calculates eithei, the specific cliclwtric constant or the spcritic rcfrwtir-c indes, the new
polarity values fall into the proper relation with respect to the solubility of the-e compounds. In this instance tlic Clausius-Mosotti specific. polarization values are not in the proper sequence and hence tio iiot corrcctly espreFs the solubility polarity relationship. This is siimmarizeti in tnhl:? 6.
1:. R(,lntionaliip 01polnu'iits of x d i nt ~ nizd oil wo/tou!(LS nitti po!ym( i ' s ii,itic 1.cspcl io zolrioilily Hnviiig discussed the first two factors, thnt of tlic direction of changi~in poh i t y of the liomologous series of norniul nionolij-chic alcohols. and of the oil polymers relative to their groivth, we are n o ~ vin ti position t o discuss tlic third i'wtoi,, that of the relntionsliip hctirecii ~ l i cpohi5tics oi tlic normnl c~!cc~hol~ (;E \vel1 :is of the otlier solvents mentioned) nntl ~lio-tiof tlie oil polymers \vit!i t'ct to their m u t u d solubilities. one considers methyl alcohol and petrolcuni etlicr as representing tlic PXtremes in polarity of tlic solvents ciiscuwd, ivith dielectric constant. of 33.7 and I .85, rebpectirely, one finds thnt methyl :~lcoliolh s little or no solvtincy for tlie ti*iglyccridc monomers, let alone tlic polyniws, n-hcre:is petrolmni ether is an c.sccllent solrent not only for the monomers but for till the polymers, t i p t o tlie g;el;ttion stag.. With r e q e c t to the lessened solubility of the higher po!yiii~rs of lo\.-t~rpolarity in thr lo\\-cr members oi the nornin! ;ilcoliol seriw of !iipht'r po!ai,itJ-, oiic s w s thnt for each stage oi polynier groi~tlicorrt>spoccling tu ;L given polarity, there is a normal alcoEiol of such pohrity as will riot csceeci tliat i.c,cluirctl for solubility. Tliiis, ior t~snmplr,n lon--polnritj- solvent s!lcIi ns tlodwyl alcohol xi11 tlissolvc the monomers :uid d l tlic poly11i~r~ up to tlie hesn11-liereas :i solvciit of relatively highor po!:irit>-. w c l i as ii-l>\1tyl alcohol. xi11 dissoiw only the monomers :uicl (liiiitxr?. The general i'ille mny tic siimmai~izedas i'ollon-s: -1lon--polarity solvent n-ill clissolve either I: high- or n lo\\,-polarity oil polymer, but ti high-polarity solrtwt will dissolve only a iiigli-polarity oil polymer. l'he tlegiw of Iiolnrity of the solvent is therefore tlw \-:iriab!e i ' x t o r , and its siiccrssivc 1on-ci.ingin tlir ascending members of the homologous series of noriiinl al(gdio1s explains their stepn-ist' sclectivc solvency on the oil pol:~~mers of incrensing rizc and proprcssively lon-ering pol:iii[!-. ?'lit> relation is further emphasized by the fact that tlic normal, seconil:iry. niitl tci.ti:iry isomers of the niono11ytli.i~a1~01101sx i t h cit'crensing po1:iritits in t l i t , order, iiariitd t>zhihit ini-t,i.icly
ing solubilitics toward tlic higher oil polyiiicvs. -1 soine\\-hat similar !:itionship ~ v a eiiotcd hy Kiincrth ( 2 2 ) in the increasing solubility of c:irbon cliositle. a highly polar conipoi~iid,iii ;L series of alcohols of increasing polarities. The reason for tlic iiiahility of tiwtoiie t o effect fractioiiation of thc oil polynit>i.s\previously rcfcvr&l t 0 . can nmi- be pircii. --iccton:e has a dielectric coll5.t ant of 21.4. ii-hich is nppvosinintcly tliat of w p o p y l al~~ohol.Thcreforct it i- ?Apnhle of dissolving csscntinlly only t he inoiioniers :ind not t he polymers. 1x3-
0
9
$z
In
8its
Q
3 0
I-
R m -rl
6
0
60
In Z
z
B
2
v)
8
L1
c
L3
4
J G D
8 E rn
0 4 Ma co
Z
-rre
07 0
1756
2634
3512
MOLECULAR WEtGHT OIL SOLUTES
FIG. 1 Relationship hetn e m polaritv expressions of solvents and molecular
R eight
of oil solutes
A graphical rcprc>entLttion of the relationship bet\\-een the solvent polarity and the molecular w i g h t s of the oil polymers is given in figure I. The i o l w n t (1 n. ordinates by both the bpecific dielectric constant and t h e specific reiractil-e indc-i. -111 points for each relationship between solvent polarity and oil moleculnr wiglit fall on -moot11 rurvc\. The iollo\ving deduction:, map be made: ( 1 I the c i i r ~e- are appro\iinately esponeiitial in form and apparently espre+ a tlivergent series; ( 2 ) tlic extrapolations of the upper ends of
POLYMER FR.ICTIOPilTION OF HEAT-POLYMERIZED OILS
621
the curves intersect a t a point the ordinate for ivhich conforms approximately to polarity values between those for ethyl and methyl alcohols; and (c3) the slope of the curves is greatest in the monomer region and least in that of the tetramer. This latter point conforms t c the experimental fractionation data, since, as is evident from tables 1 and 2 , the first fen- members of the normal alcohol series are more selective in polymer solubility than are the latter one;. 11. E X P E R I M E S T I L
*4, Fractionation of liquid hcat-polymwixed litisrc d and Toybcan oil samples
-1detailed account will noir be given of the bpecific procedures used in the fractionation of heat-polymerized linseed and soFbe:in oils. The preparation and general properties of the samples of heat-polymerized linseed and soyhean oils used in this work ]\-ill lw described in a subsequent paper. The sample. were represented by those taken immediately after each of the two oils had reached the polymerization temperature of 307°C. and by periodic samples taken thereafter up to the gelation point, as well as by those taken from the ensuing gelled oils. The fractionation of the latt'er represented a special case, since it necessitated the development of a technique for the separation of the gel-forming material M o r e fractionation of the liquid part could be attempted. This will therefore be reserved for subsequent discussion. For the initial and periodic samples up to the gelation point, the following regulnr series fractionation procedure \vas developed and used. Special tcchniqucs \vert' later deL-eloped to overcome specific difficulties which n-ere encountered in the regular fractionated series; these i d 1 be referred to as the occansion presents itself.
B.Procediirc f o r c.rtractio(i of r q u l a r s( s of liqlcid polymers Seventy-five grams of the sample I\ accurately Iveighed into :L300-nil. glass-stoppered Erlenmeyer flask, t o Ti-hich 300 nil. of ,I-propyl nlcohol vas added. The free air space was swept out ivith nitrogen (oxygen free) to prei-ent osidntion and the contents shaken x-igorously for 20 min. The estrnction flask IVRB then set aside and the contents allon-ed to settle overnight. The clear extract iras decanted into n gl -stoppered Erlenmeyer flask, covered Tvith ~ Katmosphere I of nitrogen, and set aside for evnporation. This represented the first fraction. The volume of liquid in the estraction flask IKLS madr up to 350 ml. I\-ith additionnl /!-propyl alcohol, and tlie second estraotion rcprnted in the same manner as the first. a t least three such estrsction; ivith n-propyl alcohol, the remaining insoluhle fraction is successively xrracted an equal number of times $1-ith the other members of thc liomologous alcohol series, n-butyl, n-amyl, ti-hexyl, ti-octyl, ~i-decyl,and ri-tlodecyl alcohols, or ah many of these as were required for the particular sample lieing fr.action:iterl. In spite of the care taken to keep an inert ntmospherc of nitrogen over the liqiiids during the various extractions for the pm'pose of preventing osidntion and induced polymerization: considerable difficulty \vas nevertheless erperienced during the latter part of the fractionations in that gelation occurred overnight in the
rcsitluc of tlic moi'c highly pdynicrizctl stiiiiplti. i t \\.a- ioiind lutcr that t \w adclitioii t o each estrrrction of 0.1 per cciii of +oh1 liydroc~iiinoneacted : i s :1 polynicrizntion retardant ~ i n d solved this pai.ticlnr problem. This Ivas not done, however, t o the regu1:ir scries of frnctionntioi consequently for this series it ivas not possible to extract lie!-ond the r~-hcsylor II-octyl slcohol stage. A fen- of the estrac:ioni n-ere. lio~wvei~. repented and trctited \\-ith hydroquinone, and it n.as fniincl pos+iblc to carry these fractionat iws tlirough the wdod('cy1 extraction stage without h:iving gelation tnkr placc. I n addition to the rrgular series of fractionations \vhich \\-ere all clonc ut rooni temperntiire (approximately %Y'.)! one sample of each of the tn-o hentJ-polymerized oils \vas also iractionii,tctl at :I l o w r and n higher teniperat,ure, 4°C'. and 5GcC'., in ordcr t o study the temperature clrpcndence. These will lie rderrcd t o in Section Il-. -%fter cvapoxtioii oi the solvent from thc r-arioiis extractions the resulting fractions ~ c r set c aside ( p r o p ~ r 1st~ orcd in the dark :ind in an inert utmosphcr:.) for subsequent (~eteriiiiii~iti(~1is oi nciti \-diieq 1noleciil:u w i g h t , viscosity, antl iodine value. Before taking ihis l i p :in account a-ill be given of the technique developed for the qunntit:itiw fraciionntion of thc sxiiples of the gelled oils. C'. Fractionaiio,! oj hcat-poly,iio,ixc.d gcls j o m t d j i . 0 ~ 2 l i i ~ s t c darid soylcnii oilx
The gel smipks represcntrd B considcrahlt~prohlcm with respect t o t hrir fractionation. Three fact or+ i\-crc iiivolvcti: ( 1 1 the determination of I he s p r cific materiu! causing gelation : (2'i the quantitative separation of this material ironi its allsorbed liquid phnse; nncl (-3 tlic l'rxtionation of tlie liquid phasc of the gc.1. 11-has nlrcncly \)ccn st:itccl in Section I t h n t since pctrcileiini ctlit'r 11a> t he l o w s t dielectric cvnstxit ;ind t hcreforr tlic lovwt polarit\- of the ,solvc:nts studied, its solvency for the oil pol~-nicrsof l o w s t possible polarity, i.i.., thosr, of greatest linear or br:iiiched-cli:iin length, would be a niasimum. Esperimentally, rhis I\-as borne out by the renciy solubility in pctroleum ether of all the polymerized-oil s:implcs iip to the gelation point as has previously txcn pointed out. B e c ~ u s cof this, it \\-as rensonahlc t o nssiiiiie that long linear or branched oil polymers could not tlimiselves coiistitiite the primary adsorhate but rather that some specific insolublc cross-linked polymer \vas thc primaimp cause of the gelation phenomena. Some esperiniental work on the oil-gelation problem hud previously 1iec.n done by Brnclley antl Pfann (lo), ivho s h o w d that acetone-soluble material could be cstractcd from these gels, and hy Long (24), ~ v h odemonstrated thc adsorpt ive properties of sucli gels. Seither, h o m v r , denionstrated except possibly by inference the existence of the cross-linked polymer matrix, nor was there sufficient knon-n a t the time of this previoiis work of the relationships between the polarities of solvcnt :ind the higher oil polyniers to enable these iiivestigat ors to achieve this experiment a1 fract ionat ion ohj ~c t ive . -4s a r e d t of extensive espcriment.ntion it WTI discinwed by the author: ( 1 ) t l x t a material could be qiiantitatively scpnratecl f r o m rhc oil gels hy means
P O L I M L R FR.ICTIOS.ITIOS
O F HE1T-POLYMERIZED OILS
623
of petroleum ether, ( Z i t h t this separated material possessed the physical and chemical properties of nn insoluble, infusible, cross-linked polymer, 1.3 that it was present in siibstantial amounts :is postulated in thc author's theory, and ( . j ) that there ~ r a ssubstnntial bn for believing th:it it XIS formed from the cwss-linking of relatirely short chain polymers. those a t or nr:u the pentamer > t a p (8). The lielid that this insoluble, infusible. cros.5-linkecl polymer n.ae the specific cause of ge1:ition JYW strengthened by the filct tliar tlic reriinining liquid fraction or disperse phase of the gel eshibitetl normal fluidity, complete soluhility in petroleum ether, niid lastly that it could be fractionnted, in the manner nl~wtdj-given for the liquid oil-polymer sample.;, into monornt'r.; and :in :irr:iy of polymers of increneing stages of grorrth. I). Proccjdiirc for SC porntion of iizsolitblc, iiifrcsz'hlc. cross-litiX.rd p o / y m c r iti ~itat-polyiricl,izc.rIlirisecd aiid soybc nti oil y d s 'I'lie proccdure hy d i i c h the primary sep:mition of the oil gel into i t > insoluble, infusible, cross-linked polymer phase and its adsorbed fiuid nioriomer arid polymer phase was cffected is given in the following account: ti00 g. of the hcnt-polymerizetl oil gel T Y ~ Siwighecl out into :I &liter cylindrical jar t o which ~ n gradually s atldcd with continuous stirring 4000 nil. of petroleum ether (boiling r a n g , BO-fiO'C'.!. Large niasses of t he gel rcni:iinecl iindispersed during thi:, preliminary stirring. Tlic jar JT:W then :dlon-etl to stand for 2 hr. The contents w r e then again stirred h i t without much effect 011 the dispersibility of the gel (>weptthat the petroleum ether layer lint1 I w o n i e slightly cloudy. _Ifter continued stirring for 6 lir., the gel niasses had become pnrtinlly dispcrsetl in the peti,oleurn ether layer and had consquently incrcnsetl its viscosity to tlic point ~ ~ - l i e rthe c ~ r e d t i n g estended gel TTW sufficiently rigid to support the glriss stirring rod in an upright position. Aklditionalpe~roleumether (1000 nil.) is stirred in n-ithout h i r i n g much effect 011 the gel rigidity (.wept t o thin it :I little. €Io\wver. after 90 lir. of standing ivith occnsionnl stirring tlic content'; of the jar I m a m c quite fiuid, although still cloudy. and there had sertlcil out 011 the huttom :I n-hite curdy material. -lfter :in additional (3 dnys of n1iern:l;e standing ant1 stirring Land 1 clay for find settling, the jnr contents liad separated into a perfectly clear fiuid and dense ciird layer :it tlic bottom. The clcar fluid n-2s (~:m4'tdIydecanted nncl rcser~-edfor ernporat ion. To the curdy rc.idiie, 4000 nil. of pctrolcum ether \ w s ndded nnd nllon-ed t u c s t r w t for 24 hr. \\-it11 continued stirring, after n-hicli it WL:: allon-cd to .setrle foi, 24 hr. -1test on ihc final ertraction showed only 0.1 per cent of estr:ictnble material, n-liich rernaincd cori-;tnnt on further extraction. This n'as checked v-ith tn-o hot ncetorie estrnc'tions 11-hichlikewi-e gar-e 0.1 per cent ~ i l n e s . 011this bask it n-as considercd that tile es;r:iction of soluble material from the insoluble ciii& IRIS complete. The curdy material n-as then dried to constmt w i g h t at room tcmpcraturc in ;I nitrogen atmosphere. nftcr v-hich it x i s trmsfcrrrd to a glass-stoppcrcd flask aiid stored in an inert a 7 rnoyihere. For tlir linsecd gel, tlic dried sep:ir:it ctl insoluble nintcriul represent?(: 30 per cent by m i g h t of the origirinl gel smiplt.. \ \ - h e i ~ w for the soyhrnii oil gel tlic rrcight was l i per cent. 130th gel riirtls iwrt' of .imil:ii* p q j r r t i r s : they ~ c r insole
624
I. 11. I i E R S S T E I S
uble in a wide v:zriety of solvents and infu>ible on lieating. Hence thcy could be characterized as insoluble, infusible, cross-linked polymers. -4 detailed tiescription of their specific chemical and physical properties confirming this characterization will be giren in a subsequent paper. The collected petroleum ether washings were evaporated, the final stage being done in a nitrogen atmosphere under partial vacuum. The viscous oily re?idiie after reaching constant weight T\-a. transferred t o a glass-stoppered f l a h k and stored in an inert atmosphere. The mechanism by n-hich petroleum ether disolved the adsorbed fluid phase from the insoluble cross-linked polymers can he postulated to depend on two factors: ( I ) that tlie petroleum ether is a solvent ior all the linear and hranched liquid polymers up t o the point of forniation of the insoluhle cross-linked polymers and ( 2 ) that the solution or diffusion forces l)et\wen petroleum ethrr and thesr. high liquid polymers are greater than the adsorptive or cohesive force< betn-een them and the insoluhle cws--linked polymcr :itl.orhate. To dcnion*trate the point that the wluhility iactor i- tlic m:ijor o w , cyclohexane Irith a tlielwtric constant of 2.05 a-. c.oiiiparcc1 t o 1.83 for petroleum ether in a gel-fractionation experiment identical to the a b o w gnrr only a uniformly extended gel u-ith no desorption in evidence and no ?ep:irntion of thc cross-linked polymer-. The inference can therefore he drawn that cyclohc\nnc is not I: soh-ent for the highest linear or lmmchctl oil polymer> pre?ent and thercfort cannot desorl) the gel. This inference n-ur corrohorated in the use 01 cyclohe\anc as a ci,yo.;copic >olwnt in niolecular-a-eight determinntion.;. sincc tor tlie high-polymer fraction5 :tilomalous molecular weights were ohtnined. III. D E T E R M I S ~ T I O S OF PHI fractionntetl. only a icn of tlieii more important constants w r e deteiminccl: namely, tliose \I hich were considered t o h a w a direct hearing on the general interpretation of the polymerization process as w l l a. on the calculations directed toivard arriving at the polymer distribution a t various stages of the reaction. The following constants w r e selected for thiq study: free fatty acid value, number-average molecular \\-eight (cryoscopic), ab-olute fluid viscosity, and iodine value. The follon ing i.3 a description of the analytical methods used.
-1. Free f a t t y nczd inliie There are three distinct types of acidity present in varying percentages in heatpolymerized non-conjugated vegetable oils: free fatty acid, fatty acid-triglyceride copolymers, and polymerized fatty acid (11;and unpublished data. of the author). The latter nould normally he present in negligible amount and may be dizregarded for our present purpose. The hrst two, however, are present in s u b t a n tial quantities. Since the intty acid-triglyceride copolymers are of a molecular size comparable to that of the triglyceride polymerb, thcy ran be awimed to caiise not too great an interference in the polymer-distribution aclienie t o be discussed later. On the other hand the free fatty acids, particu1:irly those nhich are pro-
POLYMER FR-\CTIOSITIOS O F HE.iT-I'OLI-AIERIZED
OILS
625
gressively liberated during the polymerization process, are only one-third the molecular weight of a triglyceride monomer, and therefore a number-average molecular weight of a mixture of free fatty acid and triglyceride monomer would have t o take this into account to arrive at the correct molecular weight of the triglyceride monomer component. Since these free fatty acids are readily qoluble they are concentrated in the n-propyl alcohol extractions. The calculation for their correction n ill be discussed later in Section lT7. The determination for free fatty acid \vas carried out in the usual manner on each of the fractions extracted I\-ith ?i-propyl alcohol and expressed as milligrams of potassium hydroxide required t o neutralize the acidq in 1 g. of sample.
B. Jfoleciilar weight Sumber-average molecular \\-eights ivere determined cryoscopically using cyclohexane as the solvent, as recommended by Gay (18). Temperatures were read on a Beckman differential thermometer to 0.01"C. and estimated t o 0.002"C. Duplicate determinations agreed t o n-ithin 1.5 per cent. control on each unbodied linseed and soybean oil g a w average values of S i 5 and 890, respectively, xvhich corresponded t o the theoretical values of 878 and 880, respectively. It should be mentioned here in p a s i n g that benzene, ir-hich has in the past been extensively used as the aolrent for these determinations, does not give reliable results, the values being conhistently lon-. -4 critical d u d y of the effect of solvents and solute concentration on the nuniber-average molecular weight of oil monomers has 4nce been made.3
C. T'iscosify (absolute) Because of the relatively small amounts obtained for many of the fractions, it n-as not possible t o use the O z t n ald method for the determination of their viscoqities. Instead comparison \\ as macle by the Gardner-Holdt Tarnish T-iscosity Tube Standards, either by the conventional bubble-rise procedure Ivherever possible or by a standardized paper-penetration method when the sample \vas too small. The latter technique enabled one t o make a determination n ith a single drop.
D. Iodine calue Iodine values were determined according t o the usual GO-min. K i j s procedure. While no experimental difficulty was noted n ith the monomer and lower polymer fractions, considerable trouble n-as experienced v i t h those of the higher polymers. This difficulty took the form of a dark b r o ~ ~precipitation n or coagulation n-hen the Wijs iodine bolution wai added t o that of the sample in carbon tetrachloride. -1pparently the higher polymers, n-hile ostensibly dissolved in the carbon tetrachloride, were present only a. a colloidal sol which flocculated in the presence of the iodine monochloride. The iodine n l u e - of the higher polymer fraction>are 3 I. AI. Bernstein. Prepiints of papers presented before the Division of Paint, 1-ariiish. and Plastics Chemistiy a t the 112th meeting of the .Iinerican Chemical Society. Ken T o r k City, September, 19.17, p 160.
626
I. hI. IJERSSTEIS
therefore of dubious v:iluc, as i d 1 he noted in the subsequent interpretation of the data given in Section IT-. IV. ISTCRPRETATIOS O F THE CXPLRIJICYT.IL D.4T.I .\SD CALCULATIOSS R E L YTISG THERETO
Eecaube of the estenzire experimental datu assembled, not all are included in this paper for reasons of cwessive length, but rather those fractionations xere selected which indicated the trend ot tlir polymerization. For linseed oil tlic samplps reported reprcvnt the rcgulni scrie> fractionations after I , G, and 10 hr. at the polymerization ti.inper:iture (tublei 7 , 8, and 91, n-hile for so;vb?
1.8
-
I-
u)
0 1.5
0
cn
1.2
0 0 -I 0.9
0.6 0.3 00
MOLECULAR WEIGHT FIG. 6. 3Iononier-polymer fractionation (26"C.), with homologous series of normal monohydric alcohols, of soybean oil heat-polymerized for 12 hr. at 307°C.
If one assumeb as a first approximation that the monomers are concentrated in the first n-propyl alcohol extracted fractions and that the iodine value of these fractions represents substantially the average of those of the monomers, the data
POLYMER F R I C T I O S - I T I O S O F HEAT-POLYMERIZED OILS
643
given in tables 18 and 19 for heat-polymerized linseed and soybean oils furnish the required evidence, both qualitative and quantitative. The correspondence of the above data to the postulated requirements of the theory is, of course, evident ; not only does the necessary qualitative relationship exist of progressively decreasing iodine value for the monomers remaining at the
3.0
2.7
m w m
24
0 2.1 a 1
> I--
1.8
cn
0 1.5
0
m
1.2 (3
0
J
0.9 0.6 0.3 1
oc 0
I
600
1200
I
I800 2400
I
I
1
3000 3600 4200 4800 5400
644
I. 31. BERSSTEIS
2. Iodine value decrease as a function of the previous history of specific polymer size -4s the polymerization reaction proceeds, utilizing more and more double bonds, one should find a progressive decrease in iodine value with increasing polymer size. This relationship for the non-conjugated vegetable oils is a complex one,
MOLECULAR WEIGHT v'2 FIG. 8. 1Iononier-polymer fractionation (26"C.), with homologous series of normal monohydric alcohols, of linseed oil heat-polymerized for 1 hr. a t 307°C.
two factors of n-hich merit some discussion. The first has t o do with the normal decrease in iodine d u e on polymerization for any particular level of unsaturation originally existing in the heterogeneous monomer oil system, while the second factor is concerned with the fact that as the level of unsaturation of the monomers decreases, the iodine value of the polymers ensuing from them should likewise be lower for any specific polymer size.
POLTJIER F R d C T I 0 6 1 T I O S O F HEIT-POLTJIERIZED OILS
645
K i t h regard to the first factor, this should evidence itself experimentally in a progressive decrease in iodine value of the polymers issuing from those monomers constituting the first reactivity group, which polymers are the first to attain the
tn W tn
I t
MOLECULAR WEIGHT v2 FIG. '3. ;\lonomer-polynier fractionation (26"C.), with homologous series of normal monoh y dric alcohols, of linseed oil heat-polymerized for 6 hr. at 307°C.
extent of growth approaching that required for the formation of the insoluble cross-linked polymers and the onset of gelation. -According t o the methodpof theoretical calculations given in a previous paper ( 6 ) for an average linseed oil
01G
I. \I. BERSSTEIZ
sample, the average iodine value of all heat-polymerized linear and branched pentamers formed from the monomers of the first reactivity group is 141. This is considerably higher than the experimental iodine value of 83.3 for the fraction
I
22
~
1
I I
I
I
I
I
extracted with n-doclecyl alcohol from a n 8-hr. heat-polymerized linjeed oil sample and is the consequence of the inapplicability of the TVij. method to the determination of unsatiu'ation in these higher polynierq. Since the experimental
POLIMER FR.'LCTIOS.iTIOS
O F HE.'LT-POLl-lIERIZED
OILS
647
iodine values of the higher polymeric fractions are n-ithout significance, one may inquire whether the correspondence between the theoretical and experimental iodine values is better a t the lo~reststage of polymer gron-th, that of dimerization. Because of the heterogeneity of monomers present, tending t o form dimers from the various reactivity groups, it is impossible to do this for any single monomer.
MOLECULAR WEIGHT
'
FIG. 11. 11onomer-polymer fractionation (26"C.), n-ith homologous series of normal monohydric alcohols, of soybean oil heat-polymerized for 5 hr. a t 30;'C.
Thih impasse leads to the possibility of interpreting the data on an averaging basis. This is related t o the .second factor mentioned,-the theoretical correspondence of the decrease in iodine value of the monomers to that of the dimers formed from them. -ks will subsequently be shown, the average of the esperimentally determined iodine values on dimerization is in reasonable agreement with the theoretically calculated average.
648
I. A I . BERNSTEIX
This second factor is illustrated by the data in tables 20 and 21, and shorn that a t successive stages of the ~ient-pol3-merizationof linseed and soybean oils the decreasing iodine n d u e of the dimer fractions qualitatively follom that of the
649
POLYMER FR.ICTIOSAITIOS OF HEAT-POLTJIERIZED OILS
oflun-arimtion. Severtlieles, even n-itli tliis limitation. the qualitative coyrespontlence is excellent. 24 2.2 2.0
1.8 1.6 v)
w
0
v, 1.4
a I
>. 1.2
tu, 0 1.0
u
v,
' 8.8 0 5 0.6 0.4
0.2
0.0
1
MOLECULAR
~
WE IGHT v2
FIG.13. 3Ionomer-polymer fractionation (%"C.!, K i t h homologous series of nilrmal nioiir,hyc!ric. a!cohols. of soj-beaii oil Iicat-pol!-mel.izcd for 17
111.. :It
307°C.
The theoretically calculated possibilities of iodine value on dimerization for Le l i n w d oil range from a maximum of 1SS for the reaction of two Le monomers LO
of the fir?t reactivity group to that of n minimum of T3 for the dimerization of Sa tn-o Le niononiers oi the third renctiJ-ity group. Similarly for soybean oil tlie 01 LO
range in iodine value on c1inieriz:itioii is from 159 for the reaction of two Id? mono-
L0 Id
0
mer5 of the hrst reactivity group t o S7 for the dinierization of two Lo monomers
Sa
l>O.l 1
177.4 1tj1 .4 lG.!) 120 .0 125 8 121.3 1'22.0 119 2 113.3
. . . . . . . . . . . . . . . . . . .
2 . . . . . . . . . . . . . . . .
a
. . . . . . .
.
G. . . . . . . . .
. ..
-
. . . . . . . . . . . . . . . . . . . . . . . . . . 10. . . . . . . . . . . . . . . . . . . . . 12 . . . . . . . . . . . . . . . . . . . . . . . . . i
e.
~~~
._ ..
~
J r . w x I!I Iodine rcrlucs of$rst 11-pi.c,p91nlcoiii>lrxl,nctcd~,.ncfio/is t i 8 (I j r i t i c f f o u of tittic of pol!ymetiruiion Heat-polyriierizcd ~ o y b c ~ oil n ~ i(?,Oi@C.', ~~~~
~~~
~
~
.~
~
111:s I n u i s I : -
~
(Original unbodied oil
~
~
~
. .
.
~
~~~~
~~
~
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14, . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . li. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . IS (liquid fr:lction of gcli . . . . . . . . . . . . . . . . . . . ~
~
~
~-
. ~ . . ~ . .~
.
~
~~
~
.~ .-
-
'hi1 ~ 1 z . 1
~~~~~
140.7 129.6 120.3 111.7 103.5 101.3
. . . . . . . . l . . . . .. . . . . . . . . . . . . . . . . . . . . . . .i.. . . . . . . . . . . . . . . . . . . . . . . . . . . F . . .. . . . . . . . . . . . . . . . . . . . . . . . . . 1
.~~
i ILLE
95.5
88.7 . . ~~. ~
.
.
~~~~~
. . . . . .
of tlie second reactivity groiik>. I t i f clenr that sonic weighted avcrages of tllc-e calculated 1-alues arc in reasonable correspondence, in a qualitative sense, with the experinleiit nl iodine vahies on dimerization a s given in the previous tables. I n addition t o tlie above qunlitntiw use of tlie espcriniental dimerization iodine value data, the>- niay be further used from a quantitatiT-e point of Tien- for the
expre..; purpore of testing the correctneb3 oi the h 4 c theoretical : i s u m p ~ion pioposed in a previous pnpcr (5) ns to the nuniber of douhle bond- 1111 o!\ ecl per oil molecule in any single nddition-polymeriz~itionI e:iction betn-een t x o nionoriier or polymer units. .kcording t o this theory it i w s po-tulated that two double bonds per oil molecule were consumed when the fatty acid component involved in the stepwise polymerization reaction was linolenic, ant1 but one \ h e n the reacting fatty acid component i w s either linolic or oleic.. T.IBLE 20 Dec,easzng i o d i n e valzie of f r a c t i o n s of heat-polynici i:ed l i n s e e d oil essentially d z m e i I C a t successiie stages of t h e i r f o r m a t z o t i T,XF. iT
3oi;c,
EXTR~CTED
. A P P R O S I X \ T E UOLECTL.IR S P Y i ' I r i DISTRIBTTIOS
FRACTIOS
1 4
-
'
8
1
6 I
~
'
BU-2 BP-1 BP-1 BCI BY-1
I I J D I S E V.ALCE O r T I R S T \I 1)s IODISE n-PROPYL ALCOHIJL E X V.4LL-E 60 XIS,) TRACTED F R A C I I O S ESS C S T I i L L ' i I I O Y O Y E RII. ''
~ s C dimer-2$ ; tiiiiier 90'; dinier-107 iiioiioriier SAC; tiiiiier-167 monomer PSC, dimer-12s monomer 9 4 7 dimer- 6 5 iiioiioIiier
133.3 124.0 121.2 120.4 130 0
161 4 129.0 125.3 121.3 122.0
T.1BLE 21 Uecreming i o d i n e value of fractiotis of heat-polymerired soybenri oil essentially d i m e r i c a t mccessiae stages C J their ~ formation TIUI:. i3 ~ 0i'C.
hours J
s 12 14
PR-4 BU-I BU-1 BP-1
965 tlimer~
~
Arc
~iioiiu~iier
~ 3 5 7dimer~ ~ C inononit'r C :I;(; dimer- 3 5 niorionicr 00C; dimer-105 monomer
113.2 10s.~ 100.0 95.0
120.3 111.; 103.5 101.3
3 . CalcLhtion of iodiiic value clecrense on nvernge climerizntiou for heat-polymerized linseed a r i d soybe:in oils l'liis discus.?ion will obviously be restricted t o that of dimerization, h u t it will not, however, be restricted t o a single species of ~ n o n o n i cnnd r dimer ensuing from it, since in this study this is not possible. The inquiry ivill ratlier be on the lissiu of the n\-erage decren;e in iodine value on ai-ernge tlimcl:,iz:ition. This is n pnrtitularly apt npprowh, since the iodine values of the imbodied oils are thernslves a!-einge .\-alms of all t lie monomers initially present niict represent the vu:ious degrees of unsaturnlion. I t ivould nppenr therdore, :is ;I tirst approximation, that the difference in iodine vdues between the :i\-t'rage of that of thr niononiers arid of :I representativt. g ~ ' o u pof thc dimers slioiild pr,ovide :in :iclequnte t e G t of
652
I . 11. I J E R S S T E I S
the theoretical requirement for decrease in iodiiie value on dimerization for tlie t\vo oil>. This is predicated on an equal iveighting of tlie iodine values of the essentially dinieric fractions, ivhich is a fair assumption. Since in linseed oil the dominant fatty acid component is linolenic acid and in soybean oil linolic acid, these two oils should on dimerization give, if the theory is correct, a decrease in iodine value equivalent t o slightly less than tTvo double bonds per oil molecule for linseed oil, because its ininor unsaturated fatty acid components are linolic and oleic, and somewhat more than one double bond per oil molecule for soybean oil, because its minor unsatiirated fatty acid components are linolenic and oleic. The average of thc experimental dimerization iodine values given in tables 20 and 21 is 124.2 and 10.5.0. respectirely, for linseed and soybean oils of the particular fatty acid component conipositions specified in the previous paper (6). Since the average iodine ~-aliieof the inonomers of the two oils is that of the unbodied oils themselves-namely, 130.1 and 140.7-we can obtain by subtraction the average decreases in iodine value on dimerization, which are therefore 55.8 and 35.8 for linseed and soybean oils. respectively. The above experimental average decreases in iodine value on dimerization for the two oils are related not only t o their major fatty acid coniponents with which JTe are primarily concerned, but to their minor fatty acid components a3 well, and it is therefore necessary t o correct for the minor fatty acid components entering into the dimerization reartion. -1fter these corrections are made, the experimental average decreases in iodine value on dimerization for the two oils, eorresponding t o the nuniher of double bonds involred, will be ready for comparison with the theoreticall!- postulated values.
4. Correction for liiiolic and oleic reacting components in theoretical decreas in iodine \-alue of linseed oil on dimerization The minor fatty acid component correction for linseed oil was made on the basis of the percentage of possible reactions for a linolic and oleic component out of the total possible renctions for each of the five LC groups (6). The results s h o ~that out of the ti3 molecules constituting a distribution analysis 11per cent will react on tlie basis of the minor linolic and oleic acid components, leaving 89 per cent of the monomers t o react through linolenic acid components. I n a previous paper ( 5 ) theoretical calculations were made which indicated that on dimerization, or any other single step of heat-polymerization of the nonconjugated vegetable oils. there occurs a decrease in iodine value of 28.94 for each double bond per oil molecule involred in the reaction. This is contrary t o the claim of Adanis and Powers (1) that in the heat-polymerization of linseed oil the loss of one double bond is e q u i d e n t t o a drop of 8ti.G in iodine value. This would imply in a reacting triglyceride monomer the loss of three doiible bonds instead of one or txvo and hence can be ruled out. Therefore, for a linolenic reacting component involving, according t o the present author’s hypothesis, two double bonds per oil molecule, the decrease in iodine value would be 2128.04)
POLYMER FRACTIOXATIOX OF HE.%T-POLTXERIZED OILS
653
or 3’7.88. Solving for the iodine value decrease on the basis of the relative percentages reacting through linolenic and (linolic and oleic) components n-e have
0.89(57.88)
4- O.ll(28.94)
= 54.7
n-hich is the theoretically calculated decrease in iodine value, based on the author’s postulates, on dimerization of a specific linseed oil corrected for reactivity by its linolic and oleic acid components. 3 . Correction for linolenic reacting component in theoretical decrease in iodine value of soybean oil on dimerization The correction for soybean oil was made on the smie basis as for linseed oil with the exception that the only reacting minor fatty acid compocent to be corrected for is the tn-o-double-bond reacting linolenic acid component. ‘The results show that of the G4 molecules constituting a distribution analysis 9.3 per cent will react on the basis of the minor linolenic acid component, leaving 90.5 per cent of the monomers to react through linolic and oleic acid components. Solving for the iodine value decrease on the tin+ of the relative percentages involved:
0.903(28.94)
+ 0.095(57.88) = 31.7
iy-hich is the theoretically calculated decrease in the iodine value, based on the author’s postulates, of a specific soybean oil iipon dimerization, corrected for reactivity by its linolenic components. The excellent correspondence betn-een the above theoretically calculated decreases in iodine value, namely, 54.i and 31.7 for dimerized linseed and soybean oil, respectively, and the respective average eyperimental values of 3S.S and 3j.8 is of course of considerable interest. It represents a direct confirniation of the postulated requirements of two and one double bond per oil molecule for linolenic and linolic polymerization reactivity, respectively. The above comparative eyperimental reaction rates of the more unsaturated monomers in the t v o oils through their various stages of heat-polymerization up to and including that of gelation may be accounted for, and in fact predicted, ab ,z consequence of the postulate given in the previous paper in this series ( 6 ) . This state.; that on the basis of the cis-trans geometric isomerism for the major fatty acid components of the tn-o oils, the reactivity of a linolenic component of the most probably reactive cis-cis-cis form is tirice that for the most probably reactive cis-trans or trans-cis forms of a linolic component. The above agreement, while pointing quite clearly to the essential correctness of the theory presented, must nevertheless not be taken as proof. The fractional separations of dimers from heat-polymerized pure linolenic triglyceride and pure linolic triglyceride n-ill provide the required rigorous proof. Kork on this specific problem is contemplated.
.\GI.> DISTRIBUTIOS
As previously stated, one of the objectives of this paper was to arrive a t some basis for quantitatii-el- determining not only the various nioiiomer weight percentage distributions as a means of follon-ing the course of the polymerization reaction, but the distribution of tlie specific polymers being formed as Iyell, For the purposes of the present paper each of the above will t o a certain extent be presented independently of the other, but where the general discussion necessitates their being considered together the terni molecitlar species-weight percetitayc d i s & i b h o n n-ill he used instead. A i sa first approsimation it is necessary t o make the assumption that for a given moleciilar w i g h t only two species are present, in any single extracted fraction,-namely, the immediate lon-er and upper stepn-ise limits. The exceptions t o this. of e o i i r . ~are . the a-propyl alcohol extracted fractions, since in these the free fatty acids constitute a third species. Since correction for these has already heen made, all fractions will tie treated on t'he basis of tlie assumption of tv-o molecular species.
-4.Basis for computitiy total tT~olcciilarspccies--ircighf p o w t i t a g e cliatributioti of heat-polynzcrizetl littseed
aiid
soybrJaii oil samples
Since several extractions Tvere made with each of the alcohols used, it was necessary t o summarize tlie entire content' of monomers, dimers, trimers, etc. from the results of the individual est'racted fractions in order t o arrive a t the molecular species dist'ribution present in the oil sample being fractionated. This m-as accomplished hy multiplying the weight of each extracted fraction by its particular species percent age distribution, udding up all the individual species contributions, and specifying them as monomers, dimers, trimers, etc. This could not be done in the regular fractionation series for polymers higher than the dimer, because tlie secondary gelation difficulty encountered, and it was therefore necessnrJ- t o Inmp t ogether the trimers and polymers higher than the trimers in evaluating the polymer gron-th for this series. It should be stated, hon-ever, that in the vases d i e r e the secondary gelation TWS eliminated, fairly complete molecular species-percentage x-eight distributions were wor1;etl out. These are given in detail in tables 22 and 23. For the regular series of fractionations, however, tlie tot nl molccnlar species distrihiitions are given in tables 2-1 and 2: on the basis alreurly mentioned. From tlie quantitative information so obtained considerable insight ivas had as to tlie changes orcurring diving the polymerization process, from its initial stage t o the end gel product. It is interesting t o note in general the main features of tables 24 and 2 5 : the progressively decreasing w i g h t percentages of monomers, the constancy of the vieight percentages of cliiiwrs except for the marked decrease near the end of thc reaction when gelation is iinniinent, niid the progressive increase in weight pcrcentages of trimer:: and polymers higher than trimers for the two oils with increasing time of polymerization. This latter point is indicated in the v d ~ i e sof 16.3 and 3 per cent after 4 :ind 3 hr., respectively, Lit tlw rcxtion lemperalwe for linseed and soybean oil in the order named, as against \-nlues of 43.7 per cent, a,nd 21.5 per cent after S hr. foi. each of the til-o oils.
POLYMER FR.A.CTIOS~~TIOSOF HE.IT-POLI-lIERIZED OILq
655
TABLE 22 d l o l e c d a r species f ra c t i o n a t i o n (!+'CJ> with Iioniologorrs .sei,ies of fZor,riccl monohydric nlcohols, of linseed oil (16-y. s a m p l e t 0.1 p e r cent h y d r o p i t i n o n e ) heaf-pol!jmeri:ed f o I ' 8 hr.. at 307°C'.
IID-2 . . . . . . DD-3 . . . . . . . .
0.81 0.3;
B. Dccreatinq w(iqhf p C m j i f n q C q of' n7ot1ovitrq
ac
2.44 1.13
~
n fiiiicfioti o j f i m c
of polgnlc/ 22n!Lorl - i t the start of the reaction one might eypect the grente-t decreaLe in moiio-
mer-, h c e here there :ire present those units possessing the highest functionality and therefore the m n i m u m reactivity. 'This is pnrticulnrly noticeable in the ('ii*c of linseed oil. For example, a t the start of the reaction-that is, in the time interval of reaching the polymerization temperature of 307"C.-a decrease of 11.1 per cent by w i g h t of monomers occurred in contrust t o the nvernge rate
656
I. M. BERNSTEIN
of decrease of only 3 pel' cent per hour after 10 hr. :it the polymerization ternpernture. Soybean oil does not conform t o this pattern at the start of the reaction, since even after 1 hr. there is practically no apparent change in the monomer T.IBLE 2.3 .Iloleci~larspecies fim-tioriatio!i \$'Cy.'!, icitk hot)iologoiis sc/.ics o.f n o r ~ ~ monohydric al alcohols, of soybean oil ( T i - g . sn!np:c 0.2 p c r cent h!idi.oqiainone 1 heat-polymerized for 17 h r .
-
ot 307°C.
JINCE)
grams
..............
D-2 . . . . . . . . . . . . . . D-3. . . . . . . . . . . . . . , D -1. . . . . . . . . . . . . DD-1. . . . . . . . . . . , DD-2. . . . . . . . . . . DD-3. . . . . . . .
'
I
0.85
(
I
0.50
I
i
1.50 0.94
1.65
l
I
' I
0.25 0.50
0.50
4.50 2.61
1.6s
0.82
6.76
--
6.75 9.14
content. This is probably clue to the presence of wsi(1iial phosphatide which, as is well l r n o ~ n acts , as a polymerization retardant. Since the nest soybean oil sample taken m-as after 5 hr. had elapsed, nothing can be said as to thc rate
POLTMZR F R . \ C l I O S . I T I O S
O F HE.IT-POLIXCRIZCD
657
OILS
T-IBLE 24 X o l e c d a r species disti ibiitiori of linseed oil heat-polymerized at 307°C. Fractionation a t 26°C. n-ith homologous series of normal monohydric alcohols T I U E AT
FRLL FITTT ACIDS
Soi'c.
TRIXERS
!\IOSOUERS
DIXERS
ISSOLCBLE
'
~
~~~~~~
TRIUERS
I V E R . I C E DE
~
L DECRE.ASE O I ~ T O T IXOSOXERS ~ ~
POLYXERS
P E R HOUR
;;#eight p c r
;eight p e r
~ _ _ _ _ _ _ _ weight per a e i g h t p e r v e i g i i i p e r ;'eigh! per
iioiirs
cent
0 ( t o 307°C). . . 1. . . . . . . . . . . . . 2. . . . . . . . . . . . .
4., ........... 6. . . . . . . . . . . . . 7.. ......... 8. . . . . . . . . . . . 9. . . . . . . . . . . . . 10. . . . . . . . . . . . . 11 (gel)*. . . . . . .
0.5 1.6 2.1 2.4 3.4 2.S 2.7 3.0 2.6 2.8
cejit
cent
cent
cerit
88.9 79.0 72.9
10.6 19.2 25.0 26.4 23,s 19.S 25 4 19.9 25.4 6.6
0 0.2 0 16.3 34.0 47.8 43.7 51.3
0 0 0 0 0 0 0 0 0 30.0
54.9 3s.s 29.6 28.2 25,s 22,s 23.7
49.2 36.0
;eight p e r ceitt
cent
11.1 9.9 6.1 9.0
11.1 21.0 27.1 45.1 61.2 70.4 71.8 i4.2 11.2 23.7 (remaining
s.l 4.0 1.4 2.4 3.0 a0.0
--
monomer) 66.0
Total. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
.
, 95.9
* The gel sample n-as fractionated at 4°C. TABLE 25 SIoleczilar species distribiitiori o j soybean oil Iieat-po/y,,iei,ired at 307'C. Fractionation a t 26°C. Ivith hoiiiologous series of norinsl monohvdric alcohols
_--ACIDS
ceiil
0.5 1.3 5 . .. . . . . . . . . . . . 2 . 6 s. . . . . . . . . . . . . . 3.1 12 . . . . . . . . . . . . . 3 . 1 14 . . . . . . . . . . . 2 . 9 16 . . . . . . . . . . . . . 2 . 5 17 . . . . . . . . . . . . . 2 . 1 1s (gel)'. . . . . . . . 2.2 1. . . . . . . . . . . . . .
UOSOUERS
DIXERS
UERSOF TRIUERS
,
'
~
LISKLD POLlXERS
cent
CLIZ!
ceiil
ceitt
99.5 9S.0
0.0 0.7 1s.5 23.5 21.7 21.6 17.9 16.4 12.0
0.0 0.0 5.0 21.5
0.0 0 0 0 0 0 0 0 17.0
Y3.9 52.0 35.0 27.7 21.6 20.3 23.3
I V E R A G E DE-I CREASE IS
ISSOLCBLE CROSS-
4SD POLY-
;.eight p e r w e i g h t p e r ameidht p e r , weight p e r ameight p e r
hours
0 (to 30i"C.). .
TRIMERS
LXLL P.~TTI
TIUE iT 3 , , i c c ,
40.0 47.8 5S.0 61.2 45.5
,
might per celil
TOT.4L DECRE.45E I S UOSOIIERS
JIOSOXERS PER HOUR
~
0 1.5 6.0 7.3 4.3 3.7 3.0 1.3 $3.0
zeigiit p e r cent
0.5 1.5 24.1 48.0 65.0 72.3 78.4 79.7 23.3 (remaining
monomer) 62.5
Total... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
, I
103.0
* The gel sample TTas fractionated at 4 T . in the presence of 0.1 per cent hydroquinone.
~
of decrease in the intervening time. -It the S-lir. reaction stage, however, the average weight percentage decrease is G per cent per hour. This then rises, follolTing the pattern observed for linseed oil, t o a maximum of 7.3 per cent after 8 hr. of polymerization. From this point on the rate diminishes, reaching a 100 -
1 1 1
90
v)
U
1
8o
w
z
,/
0
z O'
I !
I
I_, CO )'
4
/i
/c
0
1
0
I z - 60 W
0
5 50 8 n w
40
s5 30 c3
/
,' / 41 /
U
I
"SOYBEA 4
/
V
i
Y
j
IO'
I
1
I /' I
I
I
I
I'
I 1
I
FIG.14. Percentage decrease oils at 307°C.
I
~
I
iii
I
I
~
I
iiionoiiiers on licat-pol!-iiierizatiori of linseed and soybean
minimum of 1.3 per cent after 17 hr., again conforming t o the expected pattern. This information for the tn-o oils is summarized in figure 14. I t will be noted that instend of there being a still further slight decrease in the monomer content of the liquid fraction of the qeparated gels of the t.ivo oils, there is, on the contrary, an unexpected slight increae. This may be interpreted t o mean that the adsorption of the monomers onto the higher polymers during the polymerization had not been entirely deqorbed by fractionation with the
P O L T I I E R FR.\('TIOSATIOS
O F HE \T-I'OLTMERIZED
659
OILS
various estractants of the honiologous series of n o m a 1 alcohols, but that these were desorbed by the more powerful (lower polarity) petroleum ether used in the gel separation. One might be tempted in follon-ing the percentage decrease in monorners, t o study the course of polymerization from a kinetic T-ien-point and determine the order of the reaction. This has recently been done ( 2 ) , but it is questionable whether the results are significant considering the heterogeneity of the system and the varying reaction rates of its component, monomers.
C. Rates offorination of diiiicrs and higher polymers as a junction o j tiine o j polyincrization -4s has already been noted, the weight percentages of dimer for the two oils are fairly constant during the polymerization reaction. The rate of formation of the dimers is apparently equal t o that of their disappearance. The disap-
Decreasing rate
0.f
T-IBLE 26 f o r m a t i o n of trimers and polymers gmxter than trimers
HEAT-POLYYERIZED LINSEED OIL
Hours a t
30i0cc.
,
:30;'C.)
8.9 4.9
2.s
(307°C.)
Rate of formation in weight
Rate of formation in \
