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

Abstract

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 (k p) can be reliably estimated. Specifically, it is shown how k p 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 k p 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.

Investigation into the Kinetics of n‐Pentyl Methacrylate Radical Polymerization

“…polymerization processes, the propagation rate coefficient, k p , and the termination rate should be accurately known. [10][11][12] The well-established method for k p determination is pulsed-laser polymerization in conjunction with size-exclusion chromatography, PLP-SEC. [13] The k p value is obtained from maxima L i of the firstderivative curve of the molar weight distribution (MWD) measured on the product from polymerization induced by a photoinitiator under periodic laser pulsing at a precisely known laser pulse repetition rate (p.r.r.…”

“…For poly(PnMA), T g is estimated from dynamic mechanical analysis to be around 20 °C (see Figure S1, Supporting Information), which suggests that poly(PnMA) should be an attractive polymer for materials, including polymer nanocomposites and (block) copolymers, used at ambient temperature. For the design of polymerization processes, the propagation rate coefficient, k p , and the termination rate should be accurately known . The well‐established method for k p determination is pulsed‐laser polymerization in conjunction with size‐exclusion chromatography, PLP–SEC .…”

“…The first such maximum is mostly used for k p determination. The reliability of the so‐obtained k p data should, however, be verified via the internal consistency criteria: …”

On the Recovery of PLP-Molar Mass Distribution at High Laser Frequencies: A Simulation Study

“…Laser frequencies up to 100 Hz were used in most of the above-mentioned PLP-SEC experiments. Nevertheless, accurate estimation of k p from a PLP experiment is still a challenge [9]. However, the PLP-shape of the MMD (distributions with clearly defined critical points) was not obtained for acrylic monomers, specifically for n-butyl acrylate at temperatures ≥30 • C. Although it was found that by carrying out the PLP reaction at sufficient low temperatures the PLP-MMD was recovered, the origin of this phenomena was not known initially [10,11].…”

Translating Simulated Chain Length and Molar Mass Distributions in Chain‐Growth Polymerization for Experimental Comparison and Mechanistic Insight

“…[5,8] For specific applications, such as coatings, MMD bimodality has even been put forward as the primary target, leading to dispersity values higher than 4. [15][16][17] For the determination of the radical propagation, [18][19][20][21][22][23] backbiting, [24][25][26][27] and β-scission [24,28] rate coefficients or the quantification of photo dissociation quantum yields, [29] a modulated MMD trace is beneficial. In contrast to modulated and broad MMDs, the more recent chemical development of living and reversible deactivation radical poly merization (L/RDRP) mechanisms has made clear that more niche applications (e.g., drug delivery or high-end cosmetics) can benefit from lower M m values (e.g., 10 4 g mol −1 ) and narrow monomodal MMDs with Ð values below 1.5.…”