!ST,G
'YUKNEK r h P R E Y , JR., HOWARD
e. HAAS AND CHARLES w.LEWIS
for her assistance in the experimental work, and to Miss Barbara A. McNeice and Mr. William A.
Vol. 74
Steuer for the analyses reported in this paper. PITTSFIELD,
MASS.
~~
[CONTRIBUTION FROM THE INSTITUTE OF POLYMER RESEARCH AT THE POLYTECHNIC INSTITUrE O F
BROOKLYN ]
The Dehalogenation Reaction. IV. Dechlorination of the Copolymers Vinyl Acetate/ trans-Dichloroethylene and Vinyl Acetate/Trichloroethylenel BY
TURNER ALFREY,J R . , ~ HOWARD c. HAASAND CHARLES w. LEWIS RECEIVED M A Y 1, 1952
The dechlorination of the copolymers vinyl acetate/trans-dichloroethylene and vinyl acetate/trichloroethylene has been investigated The reaction of the latter is complete after six to ten hours; the former is much slower, and is not complete 'ifter three weeks.
The dechlorination of polyvinyl chloride has been shown to go to a limiting conversion of 84bCi70.j This result is in good agreement with the theoretical value, 86.47%, derived from a statistiCJtreatment based on a head-to-tail structure. It has been assumed that a head-to-head, tail-totail structure would give up 10070 of its chlorine by way of the sterically favored l12-dechlorination. The work described here was undertaken in order to evaluate the correctness of this assumption. The vic-dichloro structure that would exist in a head-to-head, tail-to-tail polymer was simulated by using a copolymer of vinyl acetate and transdichloroethylene. The copolymer of vinyl acetate :~ndtrichloroethylene was also studied. These COpolymers were dechlorinated in dioxane a t 101.5O with zinc dust by the method described in an earlier Imper of this serie5.j
case, the monomer composition was chosen which would give ' 'azeotropic" copolymeri~ation.~ The method used in following the rate of dechlorination has already been described.6 The systems studied are outlined in Tables I and 11, and the conversion data for each system are plotted in Figs. 1 and 2.
Experimental
[ZnCl +][ZnC13]/[ZnClz]2 = K I [RCl+][ZnCl' ]/[RCl,][ZnCl,] = Kt
\'inyl ,tcetste/Iruizs-dichloroethylene (16.2% C1) :inti 1 itiyl icet,itc/trichloroethylene (27 1% ' C1) were prepared iccorditig to the method of Alfrey and Greenberg.6 I n each TABLE
1
Discussion In order to interpret the results, it will be assumed that the mechanism of the reaction is the same in both cases, and that the differences in the conversion curves arise from differences in the constants governing the rate-determining step. It is reasonable to expect that the equilibrium reactions, 2~n~12
and ZnClz
ZnC1+
+ RClt
+ ZnCIs
RCl+
+ ZnCl
take place to a small extent, and are governed by the equations (1) (2)
Finally it is postulated that the rate-determining reaction is RCIf
+ Zn
--f
R
+ ZnCl+
L~ECHLORIVATIOY OF DICIILOROETHYLENE COPOLYMER and therefore (3)
d[R]/dt = k[RCI']
Here RClz represents a polymerized di- or trichloroethylene molecule, RCl+ the carbonium ion produced from it by removal of a chloride ion, and R , the dechlorinated molecule. The rate constant, lz, is a function of the amount and physical condition of the zinc used. Equations ( l ) , (2) and ( 3 ) iiiay be solved simultaneously to give
I 1-A 11-13 11-c 11-L) 11-E
I I ,776 1.'.i53 7 1 :i, 537 (;.:GI 6,761
where x is the extent of reaction. The solution of (4) is quite unwieldy, and re. 1 i I .O1 quires the simultaneous manipulation of three con.15 .01 stants in order to fit it to the data. For the present .I1 i .O1 purpose it will be more instructive to examine three . I 3 i .01 special cases A. &>> &.--In this case eq. (4) reduces to by Charles W.
1 . 000
0.16 zk 0 . 0 1
1.000
*
".0(JO
0 , 500 1 ,000
.
(1) T a k e n in part from the Ph.D. thesis submitted
Lewis Polytechnic I n s t i t u t e of Brooklyn, M a y , 1950. (2) Dow Chemical Co., Midland, Michigan (3) C. S . h l a r v e l , J H . Sample and M . F. Roy. THISJ O U R N A L . 61, 3241 (1930). (4) P . J. r'lory. ibi(!., 61, 1518 (1!13:l). (5) T.hlfrey, I I . C. IIaas and C . \ V 1,ewis. i b i d . , 73,28.51 (l!l.;ll (1;) I' Allrey and S . Greenberg, J . I'vlyiner S'i.. 3, 2!\7 ( I 9 l S b .
dx/dt = kKzK1-'/2(1 -
X)
(7) Azeotropic copolymerization occurs when t h e po!ymer formed has t h e Sam? composition a s the monomer mixture. Copolymerc formed in thi.; way have t h c xrc;il?st d?.arre of hnmonenrity. p n r tvciilwrly a t higher Clcgrcri < ? { cniivrr.iion. ( ' I I< S!riilia an I L. A \\Tall, J K r , e , i r < i i S u 1 1 . I l n r . .Sltrmi~ir,l.> 41, 521 (1
