ORGANICDISULFIDES AS INITIATORS OF POLYMERIZATION
July 5 , 1958
TABLE I1 hkl
do
do
IO for
do
loa
4.815 m+ 111 4.82 4.170 m200 4.17 2.949 s+ 220 2.948 2.514 m 311 2.516 222 2.403 2.408 w 2.085 s400 2.082 1.913 m331 1.913 1.865 m 420 1.864 422 1.702 1.702 s 1.635 m 333 1.604 1.474 m+ 440 1.474 1.410 m531 1.411 1.390 w 442 1.391 1.319 m+ 620 1.320 1.272 w533 1.272 1.257 w622 1.258 1.294 w 444 1.204 1.168 \v 711 1.168 1.157 w-640 1.157 1.115 in+ 642 1.116 a s = strong, in = moderate, rv = from A.S.T.M. card 6-0400.
22 1 100 9 4 30 4
.. 1.713 1.615 1.483 1.418
37 4 15 4 , .
1.327 1.279 1 ,265 1 211 1.175
15 1 1 6 3
.. 1.121 weak.
22 D a t a taken
X-Ray Analysis.-The compounds were investigated in powder form in hcrmetically sealed Lindemann glass capillaries in order to avoid any hydrolysis. Copper radiation (A = 1.5418) was used, filtering the @-radiationwith a nickel filter. In Table I1 are summarized the observed and calculated interplanar spacings as well as the observed2intensities of BazCa\;VOa for ocomparison. The lattice constant for SraTaOs.b of 8.34 A. is very close to that for BalCaWO6 of 8.39 A. Steward and Rooksby' found that this compound belongs to the cubic (NH&FeF~-type which crystallizes in the space group Oh5. The observed diffraction lines have either all odd or all even indices, indicating a face-centered cubic structure. Since the patterns of Sr3Ta06.Sand Ba~CawO6are essentially identical and since the concordance of the intensities is good, it can be stated that SraTa0s.s crystallizes in the same structure, that is, in the (NH4)3FeF~-type. In Table I11 are given the observed and calculated interplanar spacings for the com[ COXTRIBUTION FROM
TABLE I11 OBSERVED A N D CALCULATED IKTERPLANAR SPACINGS OF
BalCaWOsb
4.84 4.20 2.97 2.53 2.42 2.10 1 ,925
THE
3215
hkl 111 200 220 311 222 ,100 331 4 "0 422 333 410 531 442 620 j33 822 444 711 640 642
BaaTaOa.. do do 5.01 5.017 4.34 4.345 3.07 3.Oi2 2.618 2.620 2,509 2,170 2.172 1.992 1.994 1.943 1.772 1.774 1.671 1.672 1.534 1.536 1.468 1.469 1.448 1.373 1.374 1.323 1.325 1.310 1.253 1.254 1.217 1.217 1.205 1.160
IC m w s+ ws-
m s
m m+ w
m+ w w w-
m
BazLaTaOe do d, 4.98 4.97 4.32 4 . 3 1 3.06 3.045 2.60 2.599 2.50 2.485 2.16 2.155 1.97 1.977 1 . 9 3 1.927 1.76 1.760 1.66 1.658 1.53 1.522 1.45 1.457 1.436 1 . 3 6 1.361 1.313 1.300 1 . 2 5 1.243 1,207 1.195 1 . 1 5 1.151
SrpLaTaOe de do w 4.77 4.77 w 4.13 4.13 S+ 2.92 2.921 w2.49 2.492 w2.40 2.385 s2.06 2.062 w1.90 1.896 w - 1.86 1.849 s 1 . 6 9 1.689 w1.59 1.590 m + 1 . 4 6 1.461 w1.39 1.398 1 . 3 8 1.378 m i 1.31 1.306 1 . 2 6 1.261 1.247 w 1.19 1.192 1.158 1.136 m+ 1.104
Ii
IO m
m s+
mwS-
w w
s
m m+
w ww w-
w-
poun{s BazLaTa06 with a0 = 8.62 A., SrzLaTao~with an = 8.27 A . and BasTaOs.swith a0 = 8.69 A.
Discussion The reaction between stoichiometric amounts of Taz05and SrC03 or BaC08 to form Me3Ta05.6 as a pure phase, indicates that, in the case of the (NH4)sFeFe structure, there might be a similar range of anion deficient structures as has been observed for the perovskites. I n the case of tungsten and uranium, compounds like Ba3WO5.5 and BaaU05.5 can be postulated with the transition elements in the 5-valent oxidation state. Since there are four molecules per cell, a total of two oxygens are missing in the unit cell of the compound SraTaO5.6. The question as t o whether these vacancies are randomly distributed or located a t definite lattice sites can only be answered by a more precise X-ray investigation. WILMINGTON, DELAWARE
FRICK CHEMICAL LABORATORY, P R I N C E T O N UNIVERSITY]
Organic Disulfides as Initiators of Polymerization. Part 11' BY T. FERINGTON~ AND A. V. TOBOLSKY RECEIVED JULY 31, 1957 The study of the compound tetramethylthiuram disulfide (TMTD) as an initiator of the polymerization of methyl methacrylate has been extended t o 60 and 80". The experimental points are fit by the equation R'i/(cat.) = 4.80 X loL4exp(-31.6 kcal./RT). This equation falls in the same range as the similar expression for, e.g., benzoyl peroxide, although the S-S bond is much stronger than the 0-0 bond. T M T D also has a retarding effect which was studied a t 30' where the initiating effect does not appear. Retardation is due to radical attack on the T M T D molecule to produce an inhibiting T M T D radical residue. Evidence on the photoactivity of T M T D also was obtained. Various polar reagents were studied as to their effect on the rate of generation of radicals by T M T D but no pronounced change was found. A comparison with vulcanization data for T M T D indicates similar primary steps in vulcanization and polymerization by this compound. Tetramethylthiuram monosulfide ( T M T M ) was studied in the same way as T M T D a t 70, 80, 90". No retardation was found. The experimental points for initiation were fit by the equation (R'ilcat.) = 9.0 X 10l1 exp( -29.4 kcal./RT). The energy of activation is very similar to that for T M T D . Experimental observations on the photoactivity of T M T M are given. Dipentamethylenethiuram tetrasulfide was found to have a purely retarding behavior with methyl methacrylate. Diphenyl disulfide, while much less active than T M T D , shows a very similar combination of initiating and retarding ability at 100'. A mechanism is presented which fits the above observations, Retardation is due to polysulfide radical species, RS,. ( x > 1)and initiation through the intermediate radical RS.. In the case of thiuram compounds this latter is unstable and further decomposes to CS2 (CH,)N.. This mechanism is consistent with most of t h e observed d a t a on thiuram vulcanization.
+
Introduction I n the previous publication the decomposition of the compound tetramethylthimam disulfide (1) P a r t I is T . Ferington and A. V. Tobolsky, THIS JOURNAL, 7 7 , 4510 (1956).
(TMTD) was studied at 70" in the presence of the common vinyl monomers styrene and methyl (2) T h i s article is based upon a dissertation submitted by T h o m a s Ferington in partial fulEliment of the requirements for the degree of Doctor of Philosophy a t Princeton University.
'l', FERING~ON AND A. V. TOBOLSKY
3210
Vol.
so
methacrylate. I n the present paper we report more extensive studies on T M T D as well as on related compounds. The monomer methyl methacrylate has been used exclusively in these studies since it gives a higher rate of polymerization for a given catalyst than does styrene, thus lower catalyst concentrations can be studied. With this exception the experimental procedure was the same as that described in Part 1.' Experimental Results Values for Rp were obtained a t GO and SO". These are recorded in Table I and the variation of TABLEI OF METHYL METHACRYLATE INITIATED BY POLYMERIZATION TMTD -A GOO.-( T X T D ) X 108, mole/l.
7-
-----B 80°pRDa X 105, (TXTD) X lo4, R," X 105 mole/l. mole/l. s e d mole/l. see.
8.47 11.4 2.69 5.32 10.3 2.90 3.39 8.14 2.56 2.97 2.13 6.98 6.03 2.86 1.35 2.62 0.853 5.13 ,542 4.04 2.72 ,341 3.40 2.86 ,216 2.47 2.09 ,700 2.00 ,136 2.12 ,346 1.82 ,280 1.42 ,202 1.29 1.01 ,0945 .OS06 0.88 0 Corrected for thermal polyrrierizatioii using the relationship R2p.aba = R2, t h R2,,oat (1) = tiiernial rate of polymerization ill absence of R,,, th catalyst = rate of polytnerizatiori tltic to effect of catalyst Itn, 13.5 7.88 5.40 4.38 t3.15 2.16 1.75 1.26 0.861
+
onlv
I
