An alternative method to estimate the bulk backbiting rate coefficient in acrylate radical polymerization

Abstract

Based on a pulsed laser polymerization-size exclusion chromatography (PLP-SEC) analysis, an alternative method to estimate the bulk backbiting rate coefficient k_bb in acrylate radical polymerization is presented. For different solvent volume fractions (0–0.75), using the unsaturated analogue of the monomer as a solvent to rule out solvent effects, regression analysis is applied to inflection point data in the low frequency range (<ca. 100 s⁻¹) only, which can be scanned with less expensive PLP equipment. Variation of the solvent volume fraction allows the independent alteration of the average mid-chain radical lifetime and improvement in the sensitivity of the method to estimate k_bb confidently. The robustness of the method is verified considering in silico generated data including large artificial errors. The method is applied to experimental data of 2,2-dimethoxy-2-phenylacetophenone (DMPA) initiated PLP of n-butyl acrylate, taking butyl propionate as the solvent. A k_bb value of 171 ± 21 s⁻¹ (303 K) is found, in good agreement with literature data. The method presents a generic approach for the estimation of k_bb for other acrylate monomers, allows a complete statistical analysis, and can be used as a complementary tool for existing methods. In the long term, the method can even be extended for the simultaneous estimation of the bulk k_bb and mid-chain radical propagation rate coefficient k_p,m.