Relation between Specific Refractivitv of Polvmers and Atomic Structure of Polymer Unit J
J
d
RICHARD H. WILEY Lriirersity of S o r t h Caroliria, Chapel H i l l , I.C . r ,
I
tie refractive index and density data for twenty-six polj niers hate been used to determine unit refractivities,
defined as the specific refractitity multiplied by the summation of the atomic weights of the atoms in the polymer unit. These unit refractivitiesagree with values calculated a s a summation of the atomic refractivities of the atoms in the units of the polymer chain. New data are reported for p o l y vinyl chloroacetate and for the copolymer of styrene ; c i i t l maleic anhydride.
T
+
H E literature contains sc' I isolatcd i't,pr)rts that thr. siwcific refractivity of a p it'i' is rt,latcd t o the atomic -t rileturt~of t h e unit of the polymc~r chxin. The spwific- rct'txcti\-ity is ohtainrtl from thr cltsnqity anti refrartivcs iuc1c.x (lata, wingethe Lxrntz-Lorenz vquation, itnd is multiplied by I l l i t niolivxlar weight of the polynic~runit t o give a refractiyiiy ' \.:iiii(>. This value, c.allcc1 "unit rc,fi,iic.tivitj i, ;I characteristic of the po1ynit.r. It agr \ . a l i i c s obtained by a summation of t h t , atonii :{tonis i n the unit of the polymer. Such oh 1't'~I~JI'ted for polymethgl acrylatr (,.!I 1, polystyrene ( f Y ) , ruhh-r . 201. hydrorubbcr (20'1, polyethylt~rwglycols (;\, ani1 polyhita#lic,iit, ( 5 ) , 7'1) w e \vliether this relation is griirral, it jurvcy of the litcrai i i r e has heen made to collect the scattered drnsity and refracti\,(> iiitl(sx data for as many polymers as possihlc. These data, lor twnty-five polymers, along with previously unreported data f o r it tn.cnty-sixth polymer, were used t o determirie observed i i i i i t rr.fractivities. These refractivitirs n-wr found t o agree. ex-
I'd?. mer
cept for one vase noted later, with the refractivities calculated as a summation of the atomic refractivitirs of the atoms in the polymer unit. The data are summarized in Table 1. The refractive index and density data given in the literaturc (14) for polyvinyl chloroacetate gave a difference between calculated and observed refractivities of 1.02, far greater than tht: difference observed with any other polymer. The two propertiw were rrdetermincd, using a polymer prepared by benzoyl pcroxitic catalyzed hulk polymerization at 60' C. Tile polymcxrization was c a r r i d oiit under nitrogen for 2 (lays t o give a solid , Tile solid was stored at room tempcraturr, I'or 3 months to a tiubt)lr-~rc~t~ plug ( i f hard, britt I r polynic'r \vhost, tltwsiiy was 1.46 (30" C'.) and wfrac.tiw i n d w , n3: l..iO!l. \Vlitsn these valiiw ~ v ~ ri c~' > ~in v lt h r ' ri'fmctivity d~~tc~riiii~iiitirrn, the, otworved So satisand calculattd unit ri.fractivitics tlifi'c~rid tiy -O.X:1. factory explanat itrn can \IC.given for this variation. Two clicck ({eterminations were matit, ac.c.ortlingto t h o folloiving procedures, dwigntd to r('ni(~vciinpnlymerizcd monomer \vhic:li woultl lower t h c refractive index: A of film from another sample of polymer, prepared as tlt ti in the foregoing hut without stcrrage at room i c m p e r a t u r ~was . agccl :it 30" C. whicli is said to rpinove monomer from tht. polymc,r ( I O ) . Tiit: rcxfractive index iiecanie conatant at n3,3 1.50-i. A samplc of this poIymer. after tiissolving in i~tliylcnc~ dichloridc, pwcipitating with petroleum ctlicr, and drying R I 70-85" C.. h t t d a rcifractivv index of n3j 1.*511to 1.512. Tlw d a t a Foi, tli!. mipolyiwr of styrc.iir8 arid maleic anhyclride Iiave not h c w ~prc'viously rccortied. The co'polymer vas preIiarccl t)y liclating 0.1 m o l t , ciieli of styrclnc and m a l ~ ~itnliyilriilc~ ir
Unit
Densit) 1.059 I , 191 1.26
1'oly.t~ rene
I'olyvinyl a c e t a t e I'olyvinyl alcohol I'olyvinyliilene chloride l'olyainyl chloride I'ulyisohut\ lene (Vistnnex) i'oly methyl acrylate Polymethyl m e t h a c r y l a t e I'olyethyl methacrylate l'olypropi 1 rnethncrg-late Poly-n-huts1 methacrylate I'olyisobut>-l methacrylate u-Polychloroprene
I . 875 1.400 0,9125
Swprrne It ill Ihrr l i c t h y l rul,irer
Hefractivr: Index 1 , ,;SI 1. 4 6 G 1.31 1 63 1,544 '1 . .i08$1
Unit Refrac t i vi t y Obsvd. Cstlcd. Difereucc 33.17 33.33 -0.18 20.04 20.12 -0.08 10 4.5 -0 31 10.76 18.3!1 18.96 -0.37 14.03 14 10 -0.07 18.39 18.58 - 0.09 19.04 20.13 - 0 . I!) 24 22 2-1, i 5 -o.;,x 2Y 40 29,37 0.03 34.46 33.99 0.4i :38 til 3 8 . ;i9 -0.0" 0 46 :(8 f i l li9.17 2 2 $Jlj 22.87 o.O!, "2 22 87 --o 07 .I,, 22 (i3 i1 1 4 27 2 , i -il I I 27 1 4 ~
.
1.223
1 4i2:
1.19 1.11 1 06 1 .OA I 02 1 29 1 23 u !l(ll>
1.488 1.483 1 452
2 2 1.288(i
1.3
1,364
51 25
4.41 31.29
1,01331
1.4663
10 9 3
10 88
-_
1) !l"!l
Citation
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I'[,lyhcxa~~iethylenendipaniide (,l>-lon) I ' c l ~i~thyietie I ' o l ~ ~ i s o p r o p e nm ~ -elt h y l ketone t'erbunan Copolymer of vinyl chloride a n d vinyl a c e t a t e I'olyhutndiene
l'olytetrafluoroeth~-lene Cnpolynier of maleic a n h y d r i d e :ind s t y r e n e
-rF>-
I'olyetliyiene glycol
--CH2CHL-
--(----CH?CIi !
