INDUSTRIAL AND ENGINEERING CHEMISTRY
January 1953
JI
tive number of polymer molecules within a certain molecular weight range rather than the total weight of these molecules. The differential number distribution curve is obtained from the differential weight distribution function by dividing by the weight of the species. Usually the differential distribution curves of a resin are given in the form of a continuous curve. In the case of a low molecular weight resin, a more accurate picture of the distribution is obtained from a step curve rather than from a continuous curve because the molecular weight of the monomer unit cannot be compared t o the range of molecular weights in the resin. For this reason, a step differential weight distribution curve was constructed from the corresponding continuous curve for resin I. The results of the operations discussed above are summarized and the various distribution curves for resins I, 11, and I11 are shown in Figures 1, 2, and 3, respectively. SHARPNESS OF FRACTIONS. Because the presence of a variety of molecular species within individual fractions might introduce errors into the operations described above, a refractionation of a fraction of resin I was carried out in order to investigate distribution within the fraction. The resultant distribution curves indicate t h a t over 85% of the polymer fraction consists of two molecular species, and so there is very little error introduced in the distribution functions as a result of nonuniformity in the fractions.
167
RESULTS AND DISCUSSION
In studies on the polymerization of indene (6),the heats of activation of the reactions of chain propagation and chain termination were found t o be small compared t o t h a t of the chain initiation reaction. I n addition, the velocity constant of the chain termination reaction is large compared to that of the chain propagation reaction. Thus, there is a low degree of polymerization in the polymeric indenes because the growth of the average polymer chain is stopped before i t can become very long, and, therefore, no high molecular weight material can be formed. The complexity of the mathematics of the kinetics of such reactions make it impossible as yet t o calculate the distribution curves. Although a quantitative comparison between theory and experiment is not possible, a qualitative one shows good agreement. As is predicted by the theory, the average molecular weights of resins I, 11, and I11 (624, 749, and 689, respectively) are very low in the realm of polymeric substances. No molecules of high molecular weight were found because, in agreement with the reaction kinetics, the growth of large molecules isnotpermitted. No monomer or dimer is present in the resin because these were removed during the distillation. A considerable amount of trimer is present, and the most abundant species is the tetramer. These conditions are qualitatively explained by a consideration of the theory discussed above.
(Coumarone-IndeneResins)
VISCOSITIES OF THE MOLTEN RESINS E. T. PIESKI’ AND A. C. ZETTLEMOYER
M
OST of the fundamental work concerning the viscometric behavior of polymeric substances has been concerned with resins of high molecular weight such as polystyrene and polyisobutylene. There have been some indications that low molecular weight polymers behave in a manner different from that of high molecular weight polymers derived from the same monomer (9). The importance of low molecular weight resins, as evidenced by their wide use in the manufacture of such things as mastic tile and varnishes, prompted this study of the fundamental rheological behavior of these materials. The exponential type of equation relating the viscosity of a liquid t o its temperature is generally accepted both on theoretical and experimental grounds. Eyring and his collaborators ( 1 1 ) have pointed out the analogy of the elementary flow process t o a chemical reaction and have developed a theory of viscous flow on this basis by considering that a liquid is made up of molecules and holes. They found that an exponential-type equation is obtained for Newtonian liquids
where = viscosity, M = molecular weight, V = molar volume, AEvap. = heat of vaporization, A H k = heat of activation of viscous flow for the flow unit, R = the universal gas constant, and T = absolute temperature, O K. Flory (8) showed that the variation of the viscosity of high molecular weight linear polyesters with temperature and molecular weight could be expressed by a n equation of the form = 1
A R
+ Bzllz R
f
AH* RT
Present address, Experimental Station, E. I, du Pont de Nemours & Co..
Ino., Wilmington, Del.
where 2 is the “weight average chain length,” which is a measure of the average number of atoms in a chain, and A and B are constants. According to this equation, the heat of activation of viscous flow is independent of the molecular weight of the samples. I n the case of linear polyesters, AH’ attains a constant maximum value of 8 kcal., which is considerably less than would be expected for molecules as large as those present in the polymer. By comparing the 8 kcal. with the heats of activation for ordinary esters, it was concluded that linear polyester molecules flow not as 8 whole but in segments of 30 or so atoms. The value of A H k is thus determined by the flow of each segment which is approximately the same for every member of a given series. The actual viscosity, however, depends upon the chain length as shown by the 2 term in Equation 2. Equation 2 has been successfully applied tomany polymeric substances, such as linear polyesters (8), linear polyamides ( I 7 ) , polyethylene ( 4 ) )polyvinyl chloride-acetate (a), and polymeric silicones ( 2 ) . Deviations of the log viscosity-reciprocal temperature plot from linearity have been noted for polystyrene (9, 80) and polyisobutylene (9). On the basis of investigations with mixtures of linear polymers (8, Q), the effect of polymolecularity upon the viscosity-temperature relation has been reported as negligible. I n this investigation, the viscosity temperature curves were found to deviate markedly from Equation 2 and polymolecularity was noted t o have a slight but definite effect. The viscosity-temperature relationships for several commercial synthetic resins of low molecular weight, for fractions of these resins, and for mixtures of fractions were determined. Viscometric behavior was compared with the behavior expected from theoretical considerations. A mechanism to account for the observed differences is suggested.
INDUSTRIAL AND ENGINEERING CHEMISTRY
168
EXPERIMENTAL
MATERIALS. The three resins used in this study were commercial resins of the coumarone-indene type ($8). The raw materials for resins I and I1 were solvent naphthas; for resin I11 the raw material was a drip oil from a tar distillation. I n each case, the purified raw materials were polymerized a t low temperatures using aluminum chloride as catalyst. The polymerized material was washed with water t o remove the salt, then purified by steam and vacuum distillation to remove the unpolymerizable materials and the low molecular weight polymers. The distillation was continued until the desired softening point of the resin was reached.
08
-
QS-
is-2
I
~
I
I
i
I
I I I I
i
I I
I
I
i i i
I
I
i I
i ,RESINI
1
Figure 1. Differential Weight Distribution Curves for Four Resin Samples
Samples of these three resins were fractionated by double precipitation methods at 25.0' C. (93). Benzene-ethyl acetatemethanol systems were used as solvent-precipitant combinations in the fractional precipitation of these polymers. The procedure used produced a series of samples which in the case of resin I showed that about 85% of the molecules in any resin were of only two molecular species. After fractionation the samples were carefully dried by precipitation as a powder or by the frozen benzene technique ( I S ) , followed by heating in a vacuum a t 65" C. until constant weight was attained. In order t o study the effect of the shape of the distribution function upon the viscosities of molten resins, two polymer samples with special distributions were made from the fractions of resin I. With these two special mixtures, samples with four different distributions were available for study: ( 1 ) a normal distribution-e.g., Resin I ; (2) a narrow distribution-e.g., Fraction 5-12; (3) a distribution containing equal quantities of each of the available species-i.e., special mixture JS-1; and (4)a distribution possessing two widely separated maxima of approximately equal area-i.e., special mixture JS-2. The differential weight distribution curves of these four samples are shown in Figure 1. MELTVISCOSITIES. Melt viscosities in the range 0.1 t o 10,000 poises were determined using the procedure described by Flory
Vol. 45, No. 1
(8) and Fox and Flory (9). Constmt temperatures were attained through the use of vapor baths from various liquids. The viscometers were straight capillary tubes 0.5 to 3.0 mm. in diameter, each marked et appropriate distances from the lower tip. The time, t , required t o fill the capillary from one mark t o the next under a predetermined pressure differential, p , was measured. Absolute viscosities, q , in poises were calculated from the equation r]
=
ctp
(3)
where c is a viscometer constant calculated according to Poiseuille's law from the accurately measured dimensions of the tubes. The constants for the viscometers were also determined from their t p products for oils of known viscosity obtained from the National Bureau of Standards. The latter values were consistently slightly less than 2% lower than the values calculated from viscometer dimensions. The average uncertainty in the measured resin viscosities was about 2%, except a t temperatures over 200" C. where thermal decomposition of the polymers tended to increase the uncertainty to 5y0. The molten resins behaved a8 Newtonian liquids throughout the temperature and stress ranges investigated. ~IOLECULAR WEIGHTS. The molecular weights of the polymer samples were determined by the Beckmann method of freezing point depression in benzene. The ratio of the freezing point depression to the concentration was extrapolated t o infinite dilution for the calculation of molecular weights. The average uncertainty of the molecular weights was about 2% although the uncertainty in the determinations for some of the higher molecular weight samples was as high as 5'%. RESULTS
VISCOSITYAND TEXPERATGRE. The viscositias of the three commercial polymers, of fractions obtained from these polymers, and of the special fraction mixtures were measured in the range 0.1 to 10,000 poises. The viscosities from the measurements made on resin I are given in Figures 2 and 3 where the logarithm of the absolute viscosity in poises is plotted against the reciprocal of the absolute temperature. The sample designation and number average molecular weight is given on each curve. According to the well-knon-n equation log 7 = A
+ BIT
(4)
the points in Figures 2 and 3 should follow straight lines. The plots, however, show a very distinct curvature convex toward the reciprocal temperature axis. This curvature has been found t o exist to a lesser extent for other long chain compounds (8, 9, 1 9 ) ; it is considerably more pronounced with these resins and is more comparable to that found in associated liquids. Also, the viscosities of these polymers are high for materials of such low molecular weight. The slopes of all the curves become quite large a t high viscosities-that is, the temperature coefficient of viscosity becomes large. The slope, B, of the log q us. 1/T curves is related to the heat of activation of viscous flow, AH*, by the simple relationship A H * = 2.303 RB
(5)
The observed curvature indicates a decrease in the activation energy of viscous flow with an increase in temperature. The values of AH* were obtained graphically from the log 7 us. I/T curves, and these values are plotted against temperature in Figures 4 and 5. The values obtained are of the same order of magnitude as those obtained from previously published data [28 t o 47 kcal. (9$)]. All the samples show a decreasing value of AH* with increasing temperature. Resin I shows a linear decrease in A H + with increasing temperature a t higher viscosities; when the activation energy falls to a value of 15 t Q 40 kcal., the curves deviate from linearity and show a decreasing dependency upon temperature. None of the values fall below
INDUSTRIAL AND ENGINEERING CHEMISTRY
January 1953
I 0:
260
TEMPERATURE ,%. 180 140 I00
220
80
6, 7 , and 8. At low visCosities AH* is constant with changing molecular weight over the range investigated, but a t high viscosities it is not. On the 1000-poise curve for resin I, the value of AH* reaches about 60 kcal. a t a molecular weight of about 600 and remains a t this value a t higher molecular weights; a t lower molecular weights its value is lower. The heats of activation for resins I1 and I11 show a similar variation in the high viscosity curves. VISCOSITY A N D POLYMOLECULARITY. The effect of polymolecularity upon the viscosity-temperature curve has been reported as negligible heretofore (8, 9, B), but a definite dependency of the position of this curve upon the polymolecularity of the sample was noted with the resins which were studied here. Figures 2 and 3 show in every case that the viscositytemperature curves of the uniform fractions are steeper and show less curvature than the corresponding curve for the whole resin. This is emphasized by the fact that for resins I and I1 the curve for the composite resin actually crosses the curves for certain fractions of the resins. Figure 3, in which the viscosity-temperature curves of resin I, fraction 5-12, and synthetic mixtures JS-1 and JS-2 are plotted, shows that the degree of polymolecularity
60
I0 '
1 0
ul w
"-
B
169
IO'
TEMPERATURE ,'C,
I 0-
I cia
1.8
1
1
2.0
1
1
1
1
1
I/T
1
2.6
2.4
2.2
x
,
I
2.8
t
3.0
103
Figure 2. Viscosity-Temperature Curves for Resin I and Fractions from Resin I Molecular weight. and sample designations are included
15 kcal. The other resins also show a decrease in AH* with increase in temperature, but the curves ale concave toward the temperature axis with a similar decrease in temperature dependency at higher temperatures. VISCOSITY AND MOLECULAR WEIGHT.The three most widely used equations relating viscosity and molecular weight are the Dunstan equation (67, which is an empirical relationship: log
7 =
ah1
+b
(6)
Flory's equation for linear high polymers (9): log7 = a
.\/z f b
(7)
and Eyring's general theoretical viscosity equation (11): log 9 = a log M
+b
(8)
where a and b represent appropriate constants. Plotting log 9 against M , 1/%,and l o g M a t constant temperature gave similar results on all three resins; Dunstan's equation gave the most general agreement over the whole range of temperatures tested; Flory's equation was found to be applicable a t high temperatures, but not a t low temperatures; Eyring's equation gave a linear plot at low temperatures, but its slope was not the required one half and the high temperature plot was not linear. The heat of activation of viscous flow in a homologous series of polymers has been reported to attain a constant maximum value (8, 9, 11, 2.3). It is obvious from Figures 4 and 5 that the resins used in this study do not have this property a t constant molecular weight or a t constant temperature, but the dependence of the heat of activation with molecular weight a t constant viscosity is significant. The activation energies a t constant viscosities of 1, 10, 100, and 1000 poises were obtained graphically and these values were d o t t e d against molecular weight in Fimres
-
-
0
1
2.0
0
2.2
2.4 4
2.6
4
I / T X 10'
Figure 3. Viscosity-Temperature Curves for Special Distributions Molecular weights and sample designationsare included
+
is more important than the shape of the distribution curve. A radical change in the shape of the distribution curve without much change in the average degree of departure from uniformity (resin I versus mixture JS-2) has no particular effect upon the viscosity-temperature curve. Thus, the position of the viscositytemperature curve is determined principally by the molecular weight of the sample, but the degree of polymolecularity has a definite effect upon this position.
INDUSTRIAL AND ENGINEERING CHEMISTRY
170
Vol. 45, No. 1
regard to flow. For example, an extrApolation of the viscosity-temperature data of diindene as given by Zettlemoyer and Kutosh ( 2 2 ) reveals that the viscosity of this compound a t its melting point (57’ C.) is 0.142 poise. This value is about seven times the predicted value of 0.02 poise. Since the dimer of indene shows deviations from the general picture of flow as presented by Eyring and his collaborators ( 1 1 ) , the lack of agreement of the properties of the higher polymers of this compound (or of compounds similar to it) with simple theory is not unexpected. The noncomforniity of the flow of coumarone-indene polymers to the Eyring theory can be further illustrated by the calculation of the length of the segment of flow in these polymers. By the application of the ClausiusJ-I8 Clapeyron equation to published vapor pressure data 40 4 10 ( Z I ) the heat of vaporization of monomeric indene waq found to be 10.4 kcal. per mole. From this value the DllNDENE 23 2 heat of activation of viscous flow for indene is estimated t o be X 10.4 = 2.6 bcal. The graphical de00 420 440 460 4b 500 5 1 0 TEMPERATURE (‘K ) termination of the heat of activation for diindene from Figure 4, Heat of Activation of Viscous Flow us. Temperature for published data (2s)gives values of 7.5 kcal, at 790 C. Resin I Fractions and 4.7 kcal. a t 119” C. These latter values are of the order of magnitude that would be expected from Eyring’s theory. However, if the size of the moving segment in T h e temperature-heat of activation curves of the uniform the polymers being studied is obtained using the above value materials show more curvature than those of the polymolecular for the heat of activation of flow for a monomer unit in the polysamples. Also, the value of the activation energy levels off at mer chain, unusual results are obtained. The calculations show a higher value for the more uniform fractions. Thus, a t higher that any fraction from resin I having a molecular weight between viscosities the heat of activation for the uniform polymers varies 600 and 1300 and a viscosity of 1000 poises (AHi = 60 kcal.) more and a t low viscosities less than for the polymolecular resin, must have a unit of flow whose molecular weight is equal to 60 DISCUSSION kcal. i2.6 kcal. X 116 = 2700 (the molecular weight of the indene monomer unit is 116), and that any fraction of this same The Eyring theory of viscous flow ( 1 1 ) postulates that liquids resin having a molecular weight between 400 and 1300 and a are made up of molecules and holes and that the mechanism viscosity of 1 poise ( A H * = 23 kcal.) must have a unit of flow of flow consists of the motion of molecules into the holes. An whose molecular weight is equal to 23 kcal. + 2.6 kcal. X 116 = anaIogy with the process of vaporization has been made by Powell, 1030. Roseveare, and Eyring (16) w-ho discovered t h a t the free energy These high molecular weights might result from the aggregaof activation of viscous flow is less than half the energy of vaporization of molecules into groups, but this explanation would not tion and that the heat of activation is less than one third the satisfy the experimental data for several reasons: it would not heat of vaporization. Exceptions to these findings were found explain the rapid increase in the size of the flowing groups in by Ewe11 and Eyring ( 7 ) in alcohols and other associated liquids whose heats of vaporization exceeded 8 kcal. per mole. An extension of Eyring’s theory had been found necessary in the interpretation of the flow of long chain molecules. Not only was the concept of holes found necessary, but the conclusion was reached also t h a t long molecules flow in segments (8, 1 1 ) which contain about 30 carbon atoms (12). Thus, the rate of flow- of large molecules is believed t o be independent of molecular weight above a certain limiting value, except for the coordination of movement which must prevail in order for the chain as a whole to progress. An indication of the relationship between the number of holes and the viscosity was found in the brhavior of the viscosity at the melting point (12, 16). If substances upon melting expand in such a way t h a t a definite number of holes are introduced into a Iiquid and if viscosity is a function of the number of holes alone, then all substances should have the same viscosity at the melting point. A number of “simple” substances for which data were available were found t o behave in this manner (18); viscosities of these substances were about 0.02 poise a t the melting points. However, anomalies were found with compounds having long chains, and it was concluded that some factor 0 380 400 420 440 t 460 I 480 500 I other than the requirement of holes influences the TEMPERATURE (“K.) flow of these molecules (16). The data on indene and its polymers indicate that Figure 5. Heat of Activation of Viscous Flow vs. Temperature for Special Distributions these compounds cannot be clawified as simple with
i
January 1953
INDUSTRIAL AND ENGINEERING CHEMISTRY
the low molecular weight - viscositv *portion of the high curves; it would not explain the independence of the size of the groups from the size of the molecules, especially since the groups are both smaller and larger = too0 6C than the sizes of the molecules themselves; and it would not explain why the existence of the strong chemical bonds between portions of the molecules ' O r 5c could be less influential than the associative forces bez tween chains. 0 IIf the reasonable assumption is made that a t high 4 viscosities the low molecular weight molecules flow I 4 C l-as a whole while the high molecular weight ones flow UJ 49 in segments, it is possible t o determine a different heat of activation of viscous flow for the monomer &C unit and to explain the flow properties of these resins Imore reasonably. By dividing the experimentally determined heat of activation by the average number of x monomer units in the polymer chain-Le., molecular weight of polymer divided by the molecular weight of the monomer, 116--a heat of activation per monomer unit can be obtained. Although this value of the heat IC of activation of the monomer unit will not be the true value when the calculations are made for polymers which flow in segments, it should approach-the true 1 value a t low molecular weights where the polymer 200 400 6Go 800 loo0 1200 I400 molecules flow as a whole. The results of such calMOLECUL9R WEIGHT culation for points On the 'Oo0 and loopoise Figure 6. Heat of Activation us. Molecular Weight a t Constant for resin I are shown in Table I. These results inViscosity for Resin 1 Fractions dicate that the value of A H k increases with decreasing molecular weight to a maximum value of served in the viscosity-molecular weight relationships a t conabout 12 or 13 kcal. at which value it remains constant. stant temperature. The conformity of these data t o Flory's equation a t high temperatures and to Eyring's equation a t low TABLE I. HEATSOF ACTIVATION OF VISCOUS FLOW temperatures indicates a gradual transition from one mechanism (Resin I) of flow t o another. The ultimate units of flow in such a transiAH* per tion are probably the basic unit of the chain (the indene monomer Viscosity, Experimental Monomer Unit, Poises M o l . Wt. A H * , Kcal. Kca1.a unit) on the one hand, and the whole molecule on the other. 1280 5.3 1000 Another aspect of the data in which the charge in mechanism 1180 5.5 930 7.7 of flow can be observed is the variation of the heat of activation 780 9.1 620 11.3 with temperature a t constant molecular weight. As the tem12.5 500 perature increases and the size of the moving unit decreases, 13.2 430 400 13.0 the heat of activation also decreases. When the size of the moving segment approaches the size of the monomer unit, t h e activation energy varies more slowly with temperature until the segment is the size of the ultimate unit. As the temperature is increased further, no change in activation energy can be exa These values were calculated with the assum tion t h a t only whole pected. The heat of activation of the monomer unit in the chain molecules move during viscous flow, regaidless of t f e moleculltr weight of the polymer. as determined from the value a t which the heat of activation versus temperature curves appear t o level off is about 15 t o 20 kcal. This value is higher than the 13 kcal. obsevved previously. Therefore, the heat of activation of the monomer unit in the The latter value is probably more reliable, but the two values polymer chain is probably about 13 kcal. This successful calagree well enough to show that the true value is probably closer culation indicates that the previously stated assumption is probto 13 than to 2.6 predicted by Eyring's theory. The difyerence ably true. The 13 kcal. is actually about 2001, above the prebetween the two values for the heat of activation of iiow of the viously mentioned energy of vaporization of monomeric indene monomer unit is due to the fact that they were obtnined froin (10.4 kcal. per mole) but the energy of rotation in the polymer different parts of the data. The 13 kcal. was derived from the chain and the steric hindrance in the chain probably account for heats of activation at high viscosities, and because of the manner the additional energy required. If the value of 13 kcal. is corin which this value was obtained, it is probably low. On the rect, then the average segment that moves contains 4.6 monomer other hand, the 15 t o 20 kcal. was derived from the heats of activaunits a t 1000 poises, 3.5 units a t 100 poises, 2.6 units a t 10 poises, tion a t low viscosities, and because the data does not extend t o and 1.8 units a t 1 poise. Resins I1 and 111, which have strucsufficiently low viscosities, this value is probably too high. tures very similar to that of resin I, have about the same heats The difference in behavior owing to differences in polymolecof activation a t equal viscosities, so that this discussion applies ularity can be explained on the basis of the difference in flow to them as well as to resin I. mechanism. I n a polymolecular sample containing chains of The above considerations have led to the conclusion that the different lengths, the large chains are probably moving in segmechanism of flow of polyindene-type molecules changes with ments while the small chains are moving as a whole. The heat external conditions. The effects of this changing mechanism of activation of the former is as high as in a uniform polymer, but can also be observed in the various other aspects of the rheologithe heat of activation for the molecules smaller than a segment cal data presented here, For example, this change can be obis less than this value. Thus, on the average the heat of activa-
/+
Jb
171
172
INDUSTRIAL A N D E N G I N E E R I N G CHEMISTRY
70
z
g2
I
,
60 -
a 0
50-
IV'=
4 -00
(;-
820 %W
-
-
-
-
-
e +-lo V
1
2o0
1
=
1
e o I
I
1
I
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Vol. 45, No. 1
flow per monomer unit must be large enough to move the whole unit into a hole and t o cause some rotation about the C-C bonds Because of the lack of flexibility of the chain, a considerable amount of coordination is needed in order that the molecule as a whole can move in the direction of flow. The amount of coordination needed decreases with increasing temperature because the increased thermal agitation of the molecules decreases the effect of the steric hindrance of adjacent chains. When the unit of motion becomes a monomer unit there is no more decrease in steric hindrance possible, and as a result the heat of activation of viscotis flow levels off.
three low molecular weight commereial coumarone-indene resins, for fractions derived from these resins, and for certain mixtures of these fractions. The log T V S . l/Tplotsarenot linear but show a verydefinite curvature concave toward the reciprocal temperature axis. The heat of activation of viscous flow as a tunction of temperatures was determined for each sample from the slope of the log TUS. 1/T plot. These values decreased with temperature a t constant molecular weight; thevalues I of AH * leveled of€at 15 to 20 kcal. The heat 0 of activation attains a constant maximum value a t constant viscosity and a t sufficiently high molecular weights. 'Ob 200 400 600 800 1000 I200 1400 1600, The viscosity-temperature curves of samMOLECULAR WEIGHT ples having a narrow molecular weight distriFigure 8. Heat of Actjvd on us. NIolecular Weight at (:onstant 1 koo&ty for bution have greater slopes and less curvature Resin 111 Fractions than those of sampIea having a wider distribution but a similar molecular weight. The tjon is lower for the polyniolerwiar sample than for a uniform curves for samples having differing degrees of polyniolecularity c>€tencross each other. one. Also, since the smaller molecules may move as a whole at one temperature and in segments < i t another temperature, while I n order t o apply Eyring's theory of flow to the rheological properties of these polymers, a changing mechanism of flow has the longer ones move in segments at all temperatures, the heat been postulated. At low viscosities the chains apparently move of activation-temperature curves cannot be expected t o follow the same laws for both uniform aiid polymolecular samples. in segments t h a t may be as small as t h e monomer unit. At high viscosities the unit of flow is much larger and in some cases These conclusions agree with the exper,mcntal results. as large as the whole molecule itself. The viscosities and heats of activation of viscous flow of these The comparison of the heat of vaporization arid the heat of low molecular weight resins are very high compared t o the same activation of viscous flow was found to be unsatisfactory for properties for linear polymers of much higher molecular weight. the determination of the size of the segment that moves in the This apparent anomaly can be accounted for by reference t o ultimate process of flow. By analysis of the variation of the heat the molecular configuration of these materials. Indene, the of activation with molecular weight a t constant viscosity and with basic monomer of these resins, consists of a ,*yclopentadiene temperature at constant molecular weight, the heat of activaring and a benzene ring having one double bond and taw carbon tion of viscous flow for a monomer unit in a polyindene was atoms in common. I n the process of polymerization the reacfound to be about 13 kcal. The sizes of the units of flow a t tion occurs a t the second double bond of the cyclopentadiene various viscosities were calculated on the basis of this value. rings, and as a result two carbon atoms and a single bond oi the The unusual rheological behavior of the polymers is attributed resulting cyclopentadiene ring are members of both the polymer t o the fact t h a t the large side groups and the relative inflexibility chain and the five-membered ring. Thus, no rotation occurs of the polymer chain causes much steric hindrance within the about this bond, and the only articulation that can occur in the molecules and between polymer chains. nolvmer molecule must be concerned with bonds connecting t h e r--u ~ ~ - monomer units. Even this motion is sterically hindered by the ACKNOWLEDGMENT benzene rings on the chain so that the molecule probably reThe authors are indebted for the support provided by Kentile, quires considerably more than 3 kcal. (16) to rotate about this Inc-, which made this work possible, bond. The steric interference of these large side groups no doubt extends even t o the adjacent chains. -. LITERATURE CITED must be unit Of 'Ow in these The (1) Adams, H. E., and Powers, P.O., IND.Eh-a. C H E M .ANAL. , ED., the monomer unit, i.e., indene, CsHg, of molecular weight 116. 15, 711 (1943). Because of steric hindrance, the heat of activation Of viscous (2) Barry, A. J., J . A p p l i e d Phys., 17, 1020 (1946).
January 1953
INDUSTRIAL AND ENGINEERING CHEMISTRY
(3) Cragg, L €I., and Hammerschlag, N., Chem. Revs., 3 9 , 7 9 (1946). (4) Dienes, G. J., and Klemm, H. F., J. Applied Phys., 17, 458 (1946). (5) Dostal, PI., and Raff, R., 2.physik. Chem., B32, 417 (1936). (6) Dunstan, A. E., Ibid., 56, 370 (1906). (7) Ewell, R., and Eyring, H., J . Chem. Phys., 5 , 726 (1937). (8) Flory, P. J., J . Am. Chem. SOC.,62, 1057 (1940). (9) Fox, T. G., Jr., and Flory, P. J., Ibid., 70, 2384 (1948). (10) Glasstone, S., “Textbook of Physical Chemistry,” 2nd ed., pp. 646-9, New York, D. Van Nostrand Co., 1946. (11) Glasstone, S., Laidler, K. J., and Eyring, H., “The Theory of Rate Processes,” pp. 477-516, New York, McGraw-Hill Book Co., 1941. (12) Krtuzmann, W., and Eyring, H., J . Am. C h m . Soc., 62, 3113 (1940). (13) Lewis, F. M., and Mayo, F. R., IND. ENC.CHEM.,ANAL.ED., 17, 134 (1945). (14) Mark, H., and Raff, R., “High Polymers,” Vol. 111, pp. 47-63, New York, Intersdence Press, 1941.
173
(15) Pauling, L., “The Nature of the Chemical Bond,” p, 90, Ithaca, N. Y., Cornell University Press, 1940. (16) Powell, R. E., Roseveare, W. E., and Eyring, H., IND. ENG. CHEM.,3 3 , 4 3 0 (1941). (17) Schafgen, J. R., and Flory, P. J., J . Am. Chem. SOC.,70, 2709 (1948). (18) Schultz, G. V., 2. physik. Chem., B30, 379 (1935); B32, 27 (1936). (19) Souders, M., J . Am. Chem. SOC.,59, 1252 (1937). (20) Spencer, R. S., and Dillion, R. E., J . Colloid Sci., 3 , 163 (1948). (21) Stull. D. R., IND.ENG.CHEM.,39, 517 (1947). (22) Zettlemoyer, A. C., and Kutosh, S., Ibid., 36, 942 (1944). (23) Zettlemoyer, A. C., and Pieski, E. T., Ibid., 44, 165 (1952). ACCEPTED August 5 , 1952. RECEIVED for review February 25, 1952. Presented befoie the Division of Paint, Varnish, and Plastics Chemistry a t the 118th Meeting of the A M ~ R I C A CHEMICAL N SOCIETY, Chicago, Ill., September 1952. From a thesis submitted by E. T. Pieski to the Graduate School of Lehigh University in partial fulfillment of the requirements for the degree of doctor of philosophy, October 1949.
Polymerization and Copolymerization Reactions with Alfin Catalysts J
IN RELATION TO MASTERBATCH PREPARATION R. A. STEWART AND H. LEVERNE WILLIAMS Research and Development Division, Polymer Corp. Ltd., Sarnia, Ontario, Canada
P
degree of reaction was observed between t h e two methods. The bottles were shaken t o disperse the catalyst and let stand at room temperature until completion of reaction ( a t least 2 hours). Phenyl-@-naphthylamine, 1.5 parts on the monomer charged, was then added aa a 0.75% solution in methanol. The methanol destroyed any remaining catalyst while the phenyl-@-naphthylamine served as antioxidant. The polymers were removed from the bottles and washed thoroughly with water t o remove sodium hydroxide, sodium chloride, and n-pentane. Washing of t h e polymer was difficult because of its swollen nature, and some sodium chloride probably remained in t h e polymers. Conversion was determined by drying in a vacuum desiccator with continuous pumping a t room temperature. Conversion results tended to be high because of residual nonrubber materials. If these polymers were extracted by ethyl alcohol-toluene azeotrope and dried, the resulting yield fell below a calculated value of 100%. Most of the studies were done using unextracted polymers so that the true 16). conversions are somewhat lower than those reported. The results EXPERIMENTAL should not be invalidated since conclusions are drawn only when PREPARATION OF CATALYST AND POLYMERIZATION PROCEDURE.a considerable change in conversion was noted. The method of preparation of the catalyst was that used by MorThe efficiency of batches of catalyst prepared identically varied in that different quantities were required t o polymerize the same ton (9, 18). It has been found possible t o replace the 99% pure n-pentane with technical grade material (9570 purity) and t o subquantity of butadiene t o the same conversion. An arbitrary stitute a refinery cracked Ca cut for the pure propylene without classification of catalysts as good, fair, poor, and of no value loss of catalyst efficiency. The catalyst was tested by its ability has been set up; of 21 early consecutive batches, the number in t o polymerize butadiene. Eight-ounce screw-cap peroxide each category was 5, 8, 6, and 2, respectively. The catalysts of bottlm fitted with Koroseal and Butyl gaskets were used. Inthe respective classes could polymerize over 50, between 3 4 and 50, between 20 and 34, and no moles of butadiene per mole of gredients consisted of 75 grams of n-pentane, 10 grams of butadiene (approximately 97.5%), and catalyst. I n general, the “active” ingredient in the catalyst. The active ingredient was considered allyl sodium and was calculated on the basis of an charging procedure was n-pentane, butadiene, and catalyst injected by syringe and needle. I n the few other cases, the SO% yield of amyl sodium and complete reaction of the amyl pentane, catalyst, and then butadiene were charged, and the sodium with 2-propanol and propylene. Thus in the 1-liter batch bottle was immediately capped. No difference in the rate or 0.2 mole of sodium isopropoxide and 0.2 mole of allyl sodium, or
OLYMERIZATION of monomers by Alfin catalysts (8, 10, 12) has been reported as being unusual both with regard to conversion of monomer t o polymer (8, 11) and resulting polymer characteristics (3, 14). Physical tests have shown t h a t t h e properties of polybutadiene prepared from certain Allin catalysts ‘were superior t o those of polymers produced in emulsion. The properties of butadiene-styrene copolymers prepared similarly were at least comparable t o t h e properties of emulsion copolymers. These characteristics may be of value in producing polymers which will yield vulcanized stocks with good hysteresis charaoteristics or improved physical properties at high temperatures. The very high intrinsic viscosities reported (3, 8) suggested the possibility of extending the oil-masterbatch type of polymer t o even higher concentrations of oil than those used with high viscosity cold rubber under active study in 1949 and 1950. Some experiments of this type appear t o have been done (a, 14,
