Detection of PLP Structure for Accurate Determination of Propagation Rate Coefficients over an Enhanced Range of PLP-SEC Conditions

The factors influencing the periodic structure in molar mass distributions (MMDs) generated in pulsed-laser polymerization (PLP) experiments are investigated to extend the range of operating conditions under which radical polymerization propagation rate coefficients (kp) can be reliably estimated. Specifically, it is shown how kp may be determined well into conditions corresponding to the so-called low and high termination rate limits. A new parameter x is introduced to provide a convenient measure of when PLP pseudostationary conditions approach the low (x ≤ 0.2) and high (x ≥ 5.0) termination rate limits. In addition, a simple transformation is proposed to detect the PLP structure obscured by the background of the distribution under limiting experimental conditions, with simulations confirming that the methodology provides an estimate of kp with reasonable accuracy. The usefulness of the technique is then demonstrated through application to several experimental distributions. The influences of chain transfer and of chain-length-dependent kinetic parameters on the PLP structure are also systematically investigated via simulation, revealing that the principal limitation for detecting PLP structure using the methodology is size-exclusion chromatography (SEC) noise at the low and high termination rate limits