r.
\ - . I L \ - I ~.I. , c;. J.ASSSE;S~, .lsl)11. 3r.utri
Polytechnic Inslitute of B ~ o o k l y i i ,Hrookl!lri. ,Yew 1-01.k Recrii3ed 3Iny 15, 1945
Experiments on the influence of tlirinylbenzene on the polymerization of styrene \\ere carried out seI-eral years ago liy Stautlinger ct 01. (4, 5 ) :tnd siniilar studies \\-ere recently puhlished by C'h. JValling ( 7 ) . The principal result if: that copolymers containing only a fen- per cent of tlie cross-linking agent nrc illsoluble in Iwnzene, toluene, ethyl methyl ketone. etc., lint do sn-ell in such liquids. The purpose of this article is to investigate the moleculur-sizr tlisti4iution of copolymers of styrene and &vinyl deri\.atii-rs.. Divinyllienzene is difficult to olitain and prespiw in the purc 1noiio111c1'd a t e 1 Wliytc. ~Ia~infac.tulillgi~iiig ('oiiipaiiy I~i~lristriiil E'cllo\\- :it tlie I'olytcc*liiiic Iiistituto of 13r~J(JkI~Il, 1 ~ 1 . I ) I J k l ! - l I , IC\\ ~ -1lI'k. ? This palwr is :i part of a tlic iihniittecl Iiy .~\. G.. J : i i i ~ q r i i t o the f;rc.ulillgilry r ~ ft l i c x l'iilytrrhiii(>Institiit(, of 13rooklyii i i i partial fulfllinent of tlle d r ~ g r e rof A I a s t r v of Science. Jiiiic. 1045. I t s iiiaiii content \\->is prcsrntril at tlir 108th IIccxting of t h r .hiirrii*:iri ('Iicaiiiiczrl Society, S e i \ - Yot.1; ( ' i r y %Septeiiilwr, 1944. a r i i l :it t l i i x iincc>tiiigr i f tlic, l oi the frnctionation ot :ti1 uncroaj-linked qaniplc and of three polymers containing 10, 25. and 100 ppm oi diisopropenyldiphenyl The first column shons tlic nimi1)ei of the indi\idnal fraction, the second its weight, the third its intrinsic viscosity, and the fourth and fifth its molecular weight and degree of polymerization ( D P ) computed according to equation 1. From these data integral and differential molecular m i g h t distribution curve< uere constructed in the conventional way (3). Figure 3 represents the four distribution curves of polymers with 0 , 10, 25, and 100 ppm. It can be clearly seen that even as little as 10 ppm. of a dishy1 derivative exhibits a considerable influence on the shape of the molecular weight distribution curve long before it causes insolubility of the polymer. Such rlightly cross-linked polymers have :L TABLE 2 il few data characterizing the distribution c u w e s o j z’znyl-dzvinyl c o p o l y n e l s CONCESTR.ATION OF DIISOPROPEN1LDIPHEKYL
,
DP, (OBSERVED)
UP, I
IUAS)
(OBSERYED)
?Pm
0 10
25 100 300 1000
5800 6500 6600 9900 gel gel
~
1 1
(5800j 6100 6700 13300 X
1
2600 1600 1400 1200
I ~
I
29CO 2100 1500 600
so00 9000 11500 14000
I
X
higher ai-wage molecular \\eight than the normal polymer prepared under the san7.e conditions, and their distribution curve has a greater spread than t,hat of the normal polymer. Table 2 shmvs tlw \\-eight average molecular weight f i t ? ,and the c i d t h A ( D P ) , of the distribution curve at half of its masirnuin ‘height, of a normal polymer ant1 oi the threr cross-linked samples. It can he seen that both quantities increase \\-ith increasing amount of cross-linking agent. Qualit,atively this appears as a consequence of the {act that, for statistical reasons, the number of t,etrafunctional monomers in a chain \vi11 be approximately proportional t o its length. Larger iitolecules therefore contain more double bonds di3tributed along their chains unc! ha\-c LI great)er tendency t o develop a branch or R cross link than short ones. This results in a distortion of the molecular weight distribution curve t,on-ards higher DP’s. as shoxn in figure 3. Quantitatively, the theory of cross linking and gelation has been H-orked out by Flory ( 2 ) and Stockmayer (6) for polymerization processes involving the presence of several-functional niononicrs. The conditions on which their computations are based are not entirely identical n-ith those holding for a rsdical-
MOLECUL.4H-PIZE DISTRIBUTIOS OF POLYSTYRENE
469
type polymerization as investigated in this paper, but their equations contain the general tendency of cross-linking agents t o shift the average DP to higher values and t o increase the width of the distribution curve. According to Stockmayer4 the weight average DP of a cross-linked polymer is given by
\vhere a is the reacted fraction of functional groups and j represents the average functionality of the polymerizing mixture. For linear polymers equation 2 reduces to
DP,
=
l + a
(3)
Because of the small amount of divinyl derivative used in our experiments, (f - I ) is only veiy slightly larger than unity, and CY(^ - 1) is smaller than 1. Thib is the range in which still soluble polymers are obtained, the average DP of I\ hich increa,w n ith the amount of clivinyl derivative employed. To compare our results uith the clegiees of polymerization as expected by the theory, \ye have fiist detemined CY from the Dp5of the uncross-linked polymer = 3800) n-ith the aid of equation 3. One obtains a = 0.99965. I-sing this value and the ~ a l u e sf o r d as they result from the proportion of styrene-divinyl derivative (compare t d ~ l eI ) , 11-e hare then computed from equation 2 the v eight average degreeq of polynierization for the cross-linked samples. Table 2 contains in its first column the amount of cross-linking agent employed, in the second column the o h ~ e r w t l and in the third column the computed from equation 2 . It can be seen that both colunins indicate an increase of the average IIP and that the numerical values for the 10-ppm. and 25ppni. samples agree fairly closely. The larger theoretical value of 13,300 i 0 1 * the 100-ppm. sample as compared 11 ith the eipeiiniental value of 9900 may be explained by the fact that, as often in copoljinerization, the amount of divinyl derivative in the polymer I\ as not simply proportional to its concentration in the monomer mixture. It may also be cauhed by the fact that the constants K and a of equation 1 do not hold any more for polyners with as much branching as was produced by 100 ppm. of divinyl derivative. Equation 3 can also be used to predict the gel point of the copolymer; it is reached as soon a b
(m
mu,,
.f
=
l+ff 7
m,,
(4)
Reference 6 : eqriatioii 16 on page 48. T h e average U P as obtained from \risc,osit:; i i i e a s ; ~ i r ~ n i ~vi i~t ist l ithe aid of ctquatioii 1 is the visrosity average. ivhile Stockmayrr's equations !ioltl for t h e weight average. If thr exponent i n equation I is not t o o far from unity fahoi-e ( ) . i o ) ,the difference aniounts t o ahout 15-20 per rent. In using the viscosity sveragr instead of t h r weight avcragc, IYP are thereby introducing a n error of the above magiiitridc. We presiinie. however, that hei.ause of the relatively sinall number of fractions (five a n d six) in t h e rase of three of t h e samples, t i m e of t h e conclusions of this paper c a n he macle with an :irruracy better t h a n 35 or 30 per c-cnt.
because equation 4 rides the DpZtof equation 3 infinitcly Iargc; for the conditions prevailing in our expelin-ents thii ~ h o u l dhappen at about 250 ppni. of divinyl deli1 ative. Thiy is in Ear eccoitl \T it11 a prelious observation oi Staudinger and Hcuer (1). r i a h a t i n g their figure5 according to equation 4, one airi\es a t a gel point i:t 225 ppn:. of c i i ~inylbenzene in styren?. It also is confirmed by our o n n o l , ? e i ~ationq that all copolymer- containinz more than 300 ppm. of diioopi openyldiphenyl praciticall> in~olui,l: Another interesting phenorr~t~ion i:, revealed by the distribution curves of figure 3. The a1 era:e D P incrc.:i5e+ \\it11 increasing amount of cross-linking agent, ]Jut the maxinium of the distriliution curve moves t o loner DP values. This is actually predicted in the theoiieb. of Flory ( 2 ) and Stockmayer (6). Conqideiing that in our caccf 1; very cloqe to 2 , equation 14 on page 47 in Stockmayer’s paper (6) leads t o the folloiring approximate e\pression for the DP,(max) i r hich is most abundantly preqent in the polymolecular mixture :
L-sing the above values fora and f (compare table I ) , one obtains for DP, (max) the values v-hich are given in column 3 of table 2. On comparing them n-ith the d s e r v e d figures in column 4, it appears that the observed shilt of the maximum of the distribution curve towards Ion-er DP’s i q in reasonable egreement with the theoretical expectation for 10 and 25 ppm. For 100 ppm. of divinyl derivative, hon ever, the observed and calculated values for DP,, (mas) differ t o a considerable degree. They behave just as the corresponding did, and it may be that one of the explanations offered for them can also he applied for the maximum valiies.
z,
SCMLIJI.\HT
1. p,p’-DivinyldipheIiyl and p,p’-diisopropenyldiphenyl have heen prepared. They are crystalline at room temperature. but polymerize rapidly upon melting. Diisopropenyldiphenyl is stable at room temperature for a long time, Ivhile divinyldiphenyl polymerize:: in the crystalline state within a fen days. 2 . C’opolpiers of styrene u i t h 10, 25, 100, and 1003 ppm. of diisopropenyldiphenyl x e r made. ~ nnd it IT riq found that samples containin? more than 300 ppin. are practically inqo1ul)lr 3. Molecular TI eight tlist!i:?ution curve; for t h r x soluble polymer< neren-orked out. It v a s !ound that \\ ith increasing amount ot cross-linking ssent the weight a v e r q e DI’ shift7 to larger \-::lues, the most trequerit D? qhiftq t o qnialler values, and the distiibution curve flnttcn; out The authors are very much indcl:te:i t o Dr. E. Ucrgmaii Ior hi, valuable and kind help in preparing the diving1 tleiivatives, and t o XT. 19. K h y t e lor his kind interest 2nd financia1 slipport. REFERESCES >ot 65, 2 d i S (1943) (1) ALFREY,T., B A R T O V I . C\ ~, , \ \ D MARK,H.: J. A l ~ ~C hc:li l . (2) FLORY, P. J.: J. Am. Chem. Soc 63, 3083, 3091. 3006 (1941
SEPXR.1TIOK O F 1IET.IL I O S S RY CYTIOS EXCHLSGE
47 1
dEP*IR.ITIOS OF METAIL IOSS BY C-ITIOS T
H E JYI1,TOX
-1o ~ t h i ~ ~ s i cI i- )i iii i c r s i i 1 .
Rccciictl
.Iiti.c
Eioii\loti
Zllitioi?
14, 1946
It is it aell-knonn fact that metal ions are taken up preferentiallv from solution by materials capable of cation exchange. I t should, theretore. he possible to separate a mixture 01 cations of ~ a r y i n gionic size I J paszaqe ~ through an exchanger. This principle has been used hy Russell and I'earce i l ) 111 a n attempt to fractionate the rare earth+. Tests ha\ e here heen made TI ith a number of different mixtures--copper a n ~ nickci, l radmium and zinc. siiwr and copperto deteiniine n hether a practical ciuanti:xtiT e -eparation could be attained hy cation eschange. E X P L R I ~ I E \r 11,
'The cation exchange1 iiseti was the iiilfonatc 1 coal hnon n as Zeo-Karb, liicli ai firit \ra.:hed with concentrated hyclrochloric acid to remove metallic cation> and small amounts of iron oxide and then rinsed n i t h n-ater. All experiments but the last one cited ircre perlormed in n 2-ft. column of 20-mm. glass tubing, containiiig TO g. of Zeo-Kaih In the last experiment, a W t . column. containing 244 g. Zeo-Iiaiil. u a s used. I n most cases. the solution contaming R mixtiire of t n o salt.: was pa-ed through the exchanger at a rate or about 10 nil. per minute until one of the inetal ions began to appeal in the eifluent. The metals i t eie then regenerated TI itli acid, 100-mi. fiactions being collected and a!ialyzcd 130th ammoniacal :md sl~ghtiyacid solutions of varying concrntrntions v e i c tried Save typical rehiilt> m e given in table 1 11
c O ~ c 1 . ~ - ~ 1 0 ~
'Ihe fractionation of mctal ion. 17)- cation eschange does not give a quantitative separation. The methoti coulti be improved liy using a n:uch longer column, Iiut the proce- u ould thex not 1.e as practical as chemical separation. This investigation western I-nivemity.
IIXS
siipportccl by a gmni from the Abbott Fund of S o r t h 1IEFE:ItES ('E
(1) RL-SSELL.+xnPE.IWE:tJ. ~ i 1 1 1 .('hem. SOC.65, 595-600 11913).
