Version 2 2020-11-24, 14:37Version 2 2020-11-24, 14:37
Version 1 2020-04-02, 17:24Version 1 2020-04-02, 17:24
journal contribution
posted on 2020-11-24, 14:37authored byTanja Junkers, Sandy P. S. Koo, Thomas P. Davis, Martina H. Stenzel, Christopher Barner-Kowollik
The polymer product spectra of poly(butyl acrylate), polyBA, samples
obtained by full conversion bulk polymerization in the temperature
range of 60−140 °C in presence of the chain transfer agent
(CTA) octylthiol is analyzed via electrospray ionization−mass
spectrometry (ESI−MS) and quantitative 13C NMR.
The combination of both these analytical techniques allows for very
detailed information on the reaction products associated with the
formation of midchain radicals to be obtained. At 60 °C, highly
uniform polyBA is generated that consists of the structure alkyl−S−(BA)n−H. With increasing temperature, several
other peaks emerge that can be assigned to either conventional termination
product or to the three different β-scission products of the
so-called midchain radicals that are known to be formed in acrylate
polymerization via transfer to polymer reactions. Because of the formation
of β-scission products that were formed by scission to either
side of the radical functionality, intermolecular transfer to polymer
presumably plays an important role in the present system. For the
140 °C sample, 1.37 mol % of quaternary carbons on the polymer
backbone are identified with only a small fraction of the chains carrying
an unsaturated end group. As much higher levels of branching and unsaturation
are expected under the same conditions from conventional free radical
polymerization, it is concluded that the chain transfer agent is capable
of suppressing the midchain radical side reactions to a large extent.