Kinetic results at 65 ° showed that the mechanism for the polymerization of methyl methacrylate, initiated by mixtures of ammonium trichloroacetate and bis-acetylacetonato-copper(II), is more complicated than the results at 80 ° indicated. In particular, at the lower temperature there was a prominent linear termination reaction involving the initiating complex or some derivative of it. The linear termination reaction diminished in importance at hJgber temperatures. Mechanisms are suggested. The 1 : 1 complex formed by the initiator components is not the actual initiator but probably a precursor of it.
With vinyl acetate a reaction occurred but no detectable polymerization. Evidence indicated that chain inhibition rather then selective initiation was the cause. WHILE investigating the kinetic consequences of the use of two-component initiators for radical polymerization, we had cause to make use of the ammonium trichloroacetate-bis-acetylacetonato-copper(II) (CuAcac2) system discovered and characterized by Bamford, Eastmond and Rippon. cl) Our results at 80 ° substantially confirmed their findings and were apparently consistent with their proposed mechanism, cx' 2) At 65 ° the kinetic characteristics of the polymerization are different and cannot be reconciled with the Bamford mechanism in its simple form.
- EXPERIMENTAL Reagents were prepared and purified by the methods used by Bamford ~" except that we used cal" cium hydride as the drying agent instead of calcium chloride and prepared our own samples of CuAcac2 from acetylacetone and cupric acetate in ethanol, recrystailizing the raw product from benzene.
Rates of polymerizations were measured dilatometrically in undiluted monomer. Initiator components were dispensed into the dilatometers in solution, the solvent being removed by high-vacuum distillation. Monomer, from a sample previously pre-polymerized to 10-15 per cent and triply outgassed under high-vacuum (10-3 N m-z), was distilled in. The small, thin-walled dilatometers were found to attain the thermostat temperature within 3 rain of immersion. Time and contraction were measured from the moment when the thermal expansion of the dilatometer contents ceased. In experiments where contraction ensued immediately after thermal equilibration, rates were reported as initial rates (Rpo). When the induction period extended beyond the time for thermal equilibration, rates were reported as stationary-state rates (Rpsx). No photochemical effect could be detected at ambient illumination during our kinetic runs.