J O H N R E H N E R , Jr., A N D P R IS C IL L A G R A Y , Esso Laboratories, Standard O il Development Company, Elizabeth, N. J.
A procedure is described lor determining the unsaturation in Butyl rubber. The method is based on the reaction ol the polymer, in solution, with ozone to give degraded species, the limiting viscosity of which is governed by the original unsaturation. Some relevant information is given on the effects of concentration and molecular weight on the viscosity of the polymer solution, the stability of the ozonized solution, and the effects of certain addition agents. Un
saturation values based on this method and on one involving reaction with iodine chloride are correlated for Butyl rubbers containing various diolefin units.
gether w ith certain m odifications th a t have been introduced w ith th e aim of facilitating ro u tin e work.
I t was recognized th a t th e earlier procedure had th e disadvan
tage of being too tim e-consum ing, owing m ainly to th e steps in w hich th e degraded polym er solution is evaporated to dryness, an d th e residue redissolved in diisobutylene prior to th e viscosity m easurem ent. An obvious possible im provem ent w as to de
velop a procedure w hereby th e polym er solution could be ozo
nized a n d th e viscosity of th e degraded solution determ ined di
rectly, th u s elim inating evaporation an d tran sfer to a second solvent. I t was first necessary, how ever, to perform th e experi
m ents described below; th e ir significance will be explained in th e sequel. A fu rth e r sim plification was introduced th ro u g h the from d a ta obtained a t finite polym er concentrations, experim ents were carried o u t to find th e effect of concentration and m olecular w eight on th e viscosity. T he intrinsic viscosity [77 ] is defined negative slope w hich increases w ith increasing m olecular weight.
F o r polym ers of sufficiently low m olecular weight, such as are ob
tained on ozonolysis of B u ty l solutions, th e slope is observed to have a viscosity-average m olecular w eight of roughly 10,000.
C O R R E S P O N D I N G V I S C O S IT I E S O F B U T Y L R U B B E R I N C A R B O N
Calculated Molecular Weight Data (or Butyl Rubber Degraded by O zone
368 I N D U S T R I A L A N D E N G I N E E R I N G C H E M I S T R Y Vol. 17, No. 6 sta n d in glass-stoppered containers u n til th e following day. The polym ers were th e n recovered by evaporation an d th eir u n satu ratio n values determ ined from th e respective viscosities in di
isobutylene. T he experim ent was repeated w ith a second sam ple of th e sam e polym er. T h e average u n sa tu ra tio n values are given in T able I I . I t is seen th a t, w ithin th e experim ental error, no
^ c 8Hl6
Figure 2. Corresponding Values of Intrinsic Viscosity in Carbon Tetrachloride and in Diiso
butylene
Table III. Effects of M illing and Addition Agents on Unsaturation Values of Butyl Polymers no significant influence on th e determ ined values.
A P P A R A T U S A N D P R O C E D U R E
The ozone generator is of th e fam iliar Siemens ty p e and is oper
ate d a t 15 kilovolts.
In order to obtain higher ozone concentrations, oxygen is used in preference to air. Com m ercial oxygen is tak en from a cylinder through a reduction valve an d is passed, in tu rn , through 30%
sodium hydroxide, D rierite, a flowmeter, a n d into the generator.
T he ozonized gas passes from th e generator through 30% sulfuric acid, anhydrous calcium chloride, and in to a glass manifold. A flow ra te of 10 to 15 cc. per second is comm only used; this m ay be varied considerably an d is n o t critical. T he ozone concentra
tion depends on th e flow rate, as well as on th e particu lar genera im mediate vicinity, and on th e delivery side, of th e generator are joined w ith K oroseal tubing. (The authors are indebted to T. L.
G resham of the B. F. Goodrich Com pany for a supply of this tubing.) E arlier a tte m p ts to use all-glass connections led to ex
cessively rigid equipm ent.
June, 1945 A N A L Y T I C A L E D I T I O N 369 T he dry ozonized gas passes into th e end of a tu b u la r glass
m anifold which distributes th e gas stream in to th e ozonizing tubes through three side arm s. (The num ber of side arm s an d ozoniz
ing tu b es can doubtless be increased an d th u s be ad ap te d to the requirem ents.) E ach connection betw een th e m anifold side arm s an d th e ozonizing tu b es is m ade flexible by inserting a piece of Koroseal tubing. T he side arm s are equipped w ith stopcocks, so th a t each tu b e m ay be rem oved w ithout disturbing th e opera
tion. T he end of th e m anifold is equipped w ith a stopcock, so t h a t th e ozone stream m ay be by-passed. T he gas stream s issu
ing from the ozonizing tubes are united in an exit manifold similar to th a t described, and pass into the laboratory hood.
The ozonizing tubes are held by suitable clam ps in a n ice-water m ixture contained in an insulated rectangular trough equipped w ith a fitted cover an d a drainage valve. T he tubes are m ade of Pyrex, as shown in Figure 3. T he dim ensions are such th a t each tu b e will contain 100 cc. of liquid when filled to a calibration m ark near th e m idpoint of th e neck.
D uring the ru n some solvent loss through evaporation takes place, and it is necessary to m ake up th e resulting solution to a definite concentration for th e subsequent viscosity m easurem ent.
T his is accom plished by calibrating each tu b e a t 25°, 30°, and 35° w ith 159.50 gram s of carbon tetrachloride (which occupies exactly 100 cc. a t 20°, th e tem perature of th e viscosity m easure
m ent). T h e ozonized contents m ay th en be diluted to exact volum e a t any know n room tem p eratu re; visual interpolation is sufficiently exact for interm ediate tem peratures.
In m aking a ru n three solutions are prepared for each lo t of B u ty l ru b b er; these are ozonized for 1, 2, and 4 hours, respec
tively. Samples weighing a b o u t 1.5 gram s are weighed to the nearest m illigram and are dissolved in roughly 40-cc. portions of carbon tetrachloride by tum bling for 48 hours in glass-stoppered containers. E ach solution is th en transferred to an ozonizing tube, th e residual solution being washed in w ith tw o 10-cc. por
tions of th e solvent. T he tubes are clam ped into position in the ice-water m ixture an d ozonized oxygen is passed through the ap p a ra tu s a t a ra te of 10 to 15 cc. per second, th e rates through th e separate ozonizing tu b es being occasionally equalized by ad
ju stm en t of th e stopcocks. T he rate of cooling of the solution is sufficiently fa st to perm it ozonization im m ediately after im m er
sion of th e tubes in the cold bath.
A fter one hour the first tu b e is rem oved from the apparatus, ozonization of th e others being allowed to continue for the longer periods. A stream of air is passed through the contents for about 15 m inutes in order to sweep o u t excess ozone, and a fter th e con
te n ts have been allowed to stan d a t room tem perature for a to tal tim e of a t least 0.5 hour th ey are diluted to exact volum e w ith carbon tetrachloride, thoroughly mixed, an d th e viscosity a t 20°
determ ined w ith a Ubbelohde suspended-level viscom eter, proper account being taken of the kinetic energy correction.
T R E A T M E N T O F T H E D A T A
T h e ratio of th e viscosity of th e solution to th a t of th e solvent gives th e relative viscosity, ijr; from th is and th e concentration, c, of th e polym er, [77] is calculated by E q u atio n 1. D ividing th is value by 1.255 (E quation 2), gives th e corresponding intrinsic viscosity in diisobutylene. T he values th u s obtained for th e th ree solutions are p lo tted against tim e of ozonization; curves such as are shown in Figure 4 are obtained. T he linear portion of th e curve, w hich usually occurs betw een th e 2- and th e 4-hour points, b u t which occasionally includes th e 1-hour point, is ex tra
polated to zero tim e. F rom th e in tercep t th e viscosity-average molecular w eight, Mv, of th e degraded polym er is obtained from the following relation (I):
log M , = 5.378 + 1.56 log [,] (3) T he num ber-average, m olecular w eight M n is th e n given (4) by th e relation
M n = M v/ 1.832 (4)
•and th e u n satu ratio n , U, of th e original polym er, expressed as
HOURS
Figure 4. Typical Ozonization Curves
Figure 5. Correlation of Unsaturation Values for Butyl Rubbers Containing Various Diolefin Units
370 I N D U S T R I A L A N D E N G I N E E R I N G C H E M I S T R Y Vol. 17, No. 6
m ately tw ice as large as those obtained by th e ozonolysis m ethod, an d it has been suggested (4) th a t th e difference is due to factors, investigated, these m aterials show linear relationships betw een U (ozone) an d U (IC l), although th e slopes differ by a b o u t 20%.
In view of th e well-known influence of su b stitu e n t groups on th e course of th e reaction of an olefin w'ith halogens, these differences are n o t surprising.