Determination of propagation rate coefficients for methyl and 2-ethylhexyl acrylate via high frequency PLP-SEC under consideration of the impact of chain branching

The radical propagation rate coefficients, kp, of methyl acrylate (MA) and 2-ethylhexyl acrylate (EHA) have been determined in bulk via high frequency (500 Hz) pulsed laser polymerization coupled to size exclusion chromatography (PLP-SEC) up to elevated temperatures (20 ≤ T/°C ≤ 80). Prior to the analysis of the generated polymeric material, an investigation into the branching behavior of the generated polymers has been undertaken, employing the concept of local dispersity, D(Ve). In addition, the Mark-Houwkink-Kuhn-Sakurada parameters for both poly(MA) and polyEHA were determined at each studied reaction temperature. The temperature averaged values read (K = 10.2 x 10-5 dL g-1; α = 0.741) and (K = 9.85 x 10-5 dL g-1; α = 0.719) for poly(MA) and polyEHA, respectively. The local dispersity data indicate that branching in polyEHA may be considerably more prevalent than in poly(MA), as with increasing temperature polymer microinhomogeneities are observed. Consequently, the Arrhenius parameters for kp of EHA are beset with a larger error than those of MA. The activation parameters in the temperature range between 20 and 80°C read: EA MA = 18.5 (+0.8 to -0.9) kJ"¢mol-1 and AMA = 2.5 (+1.2 to -0.6) x 107 L"¢mol-1"¢s-1; EA EHA = 15.8 (+1.6 to -1.4) kJ"¢mol-1 and A EHA = 9.1 (+10.1 to -2.9) x 106 L"¢mol -1"¢s-1.