SP-PLP-EPR Investigations into the Chain-Length-Dependent Termination of Methyl Methacrylate Bulk Polymerization

Termination kinetics of methyl methacrylate (MMA) bulk polymerization has been studied via the single pulsed laser polymerization-electron paramagnetic resonance method. MMA-d(8) has been investigated to enhance the signal-to-noise quality of microsecond time-resolved measurement of radical concentration. Chain-length-dependent termination rate coefficients of radicals of identical size, k ti,i, are reported for 5-70 °C and up to i = 100. k ti,i decreases according to the power-law expression $k_{\rm t}^{i,i} = k_{\rm t}^{{\rm 1,1}} \cdot i^{ - \alpha }$. At 5 °C, k(t) for two MMA radicals of chain-length unity is k t1,1 = (5.8 ± 1.3) · 10(8)  L · mol(-1)  · s(-1) . The associated activation energy and power-law exponent are: E(A) (k t1,1) ≈ 9 ± 2 kJ · mol(-1) and α ≈ 0.63 ± 0.15, respectively.