A study of 2,3-dichloro-[formula omitted]-xylylene polymerization kinetics using high-vacuum in situ differential scanning calorimetry

Abstract

The polymerization kinetics of 2,3-dichloro-p-xylylene was studied by in situ non-isothermal DSC measurements with a custom-made heat-flux calorimeter integrated into a vacuum vapor deposition polymerization reactor. The total exothermal effect of polymerization reaction (ΔH=57±6kJmol−1) and its temperature range (−155 to −80 °C) were evaluated. In contrast to polymerization of unsubstituted p-xylylene, DSC reveals a complex shape of the polymerization peak for 2,3-dichloro-p-xylylene, consisting of two overlapping individual peaks. It was suggested that the first peak is associated with polymerization reaction starting from active radical centers formed during the deposition stage, whereas the second peak is connected with polymerization starting from active centers initiated during heating of the monomer condensate. The Fraser-Suzuki deconvolution procedure was used to separate these two processes. The differential isoconversional method by Friedman was applied for the kinetic analysis. It was found that for both of the processes the effective activation energy drops at high conversion degrees from about 25–27kJmol−1 to about 14kJmol−1. Such behavior can be explained by transition to diffusion-controlled regime of the reaction due to vitrification of the polymer-monomer reaction mixture.