Trideuterovinyl acetate

Rp k 2 (10), and thus the relative change in rate should be proportional to the square root of the isotope effect. We felt that synthesis and polymerization of two partly deuterated vinyl acetates, trideuterovinyl acetate (D CD - OAc) and vinyl trideuteroacetate =CH-0-C-CD ) cou settle the question... 

If it is the acetyl group, when CD COOCH CH is used there will be an increase of the molecular weight compared to undeuterated vinyl acetate. On the other hand, if the polymerization of trideuterovinyl acetate shows the molecular weight increase, then the vinyl hydrogens are implicated. Also, it is expected that the emulsion polymerization rate would rise when trideuterovinyl acetate is used, if chain transfer on this site is important as we believe (10). 

Bulk Polymerization The conversion versus time plot for the bulk polymerizations of vinyl acetate and its deuterated analogues is shown in Figure 1. Vinyl tridueteroacetate has a conversion rate of 9.9 x 10 3/min which is identical with that of vinyl acetate (9.5 x 10 3/min) within the experimental error. However, trideuterovinyl acetate has a much higher conversion rate (1.69 x 10 2/min). The ratio of the rate of polymerization of tridueterovinyl acetate to the average of the other two monomers is 1.74 -. 03. 

Vinyl acetate and vinyl trideuteroacetate were run together, while trideuterovinyl acetate was run later. The lag shown in the first two is almost certainly not due to residual oxygen, as this... 

The rate of polymerization in emulsion polymerization is proportional to kg-, where kg is the fhain transfer step on the vinyl group (10). Substituting trideuterovinyl acetate for vinyl acetate raised the rate by a factor of 1.76. When the calculation for the isotope effect on rate is done accurately, taking into account the 3% H on the trideuterovinyl, we find that if the effect is purely on k3, the rate should rise by a factor of 1.69 as compared to 1.76 . 02. This is almost within the experimental error. There may be a very slight secondary isotope effect (23,24) on the propagation and re-ini tation rate constants k2 and k, but it cannot be decided from these data. 

Thus an increase of polymerization rates by (k /k T and molecular weight by k3/k3p should be observed when trideuterovinyl acetate is used (k3J) is the chain transfer rate constant for trideuterovinyl acetate). 

We have seen in Tables 1 and 2 that both the polymerization rate and molecular weight of trideuterovinyl acetate increased compared to that of vinyl acetate. Since the rate increase is identical for bulk and emulsion polymerization and we know that almost all termination in emulsion polymerization is between monomer and growing radical (10), the implication is that the same is true in bulk polymerization. While this conclusion is initially surprising, it supports our argument that the vinyl radical is reasonably stable (10). Otherwise the radical would reinitiate rapidly and its concentration would be too low for termination with it to be important. 

The bulk polymerization rate of trideuterovinyl acetate was found to be 1.78 times that of vinyl acetate. In emulsion polymerization the same result was found. The molecular weight of poly(trideuterovinyl acetate) was 2.59 times that of poly(vinyl acetate). The overall isotope effect on chain transfer to monomer was calculated to be 3.04. Chain transfer was shown to be 94% on the vinyl hydrogens and 6% on the acetyl hydrogens. The measurement of polymerization rates in emulsion polymerization showed that the chain transfer on acetyl hydrogens is kineti-cally insignificant. 

However, a different mechanism had been suggested by Litt and Chang [27]. By using vinyl trideuteroacetate and trideuterovinyl acetate, they indicated that more than 90% of the transfer occurs at the vinyl hydrogens ... 

---