Electrospray ionization mass spectrometry (ESI-MS) is used to analyze poly(butyl acrylate) samples at full conversion obtained by bulk free radical polymerization in the temperature range of 60-140 °C in the presence of the chain transfer agent (CTA) 1-octanethiol at concentrations varying between 0 and 0.4 mol ·L-1. Termination by combination products carrying initiator and transfer-derived fragments as well as three β-scission products were identified in the accessible mass range of up to 2000 mlz. The resulting mass spectra are subsequently quantitatively evaluated via integration to assess product distributions as a function of varying reaction conditions, that is, different temperatures and CTA concentrations. The present study provides for the first time quantitative product distribution data for butyl acrylate polymerization. The main species of interest, defined to be those most sensitive to variations in temperature, CTA concentration, or both, are identified to be thiol-capped polymers (TCPs) produced by the interference of the CTA in the polymerization and β1, the β-scission product produced by chain cleavage of so-called midchain radicals formed via transfer to polymer reactions. Relatively high concentrations of 1-octanethiol produce a very uniform thiol-capped polymer, whereas low concentrations of thiol produce a very large number of β-scission products. Increasing the reaction temperature increases the proportions of β-scission products, and increasing the CTA concentration can suppress and control the amounts and types of species formed to the point where the product spectrum is almost quantitatively constituted of the TCP product. Other species found include conventional termination via combination products and small amounts of β-scission products with initiator end groups. The quantity of combination products has no significant variation under the range of conditions studied, and they are thus considered minor products. The data provided in the present study can constitute the basis for the further quantitative evaluation of reliable rate coefficients for midchain radical formation and depletion pathways.
|Number of pages||8|
|Publication status||Published - 13 Jan 2009|