On the Termination Mechanism in the Radical Polymerization of Acrylates

Abstract

In a recent publication, Nakamura and co-workers studied the termination mechanism in the radical polymerization of acrylates. Contrary to conventional thinking, their conclusion is that termination is overwhelmingly by disproportionation. This finding impacts on a large body of the previous work in the polymerization of acrylic monomers which this work seeks to address. Analysis of the molecular weight distribution of acrylic polymers obtained under different polymerization conditions shows that termination by combination is the more probable mechanism for mutual termination of secondary radicals. It is proposed that in the experiments conducted by Nakamura and co-workers, backbiting plays a key role and their experimental data are reinterpreted, showing that they are more revealing with respect to the mode of termination of the midchain radical produced by backbiting, than to bimolecular termination of secondary radicals.

Catalyzed Radical Termination in the Presence of Tellanyl Radicals

“…and pSt . radicals, it was surprising to find that acrylate radicals resulting from a pMA−TePh macroinitiator terminate almost exclusively (99 %) through Disp, in contrast with several other previous and subsequent reports. In the most recent contribution, it was shown that the product distribution depends on the reaction medium, a greater viscosity resulting in an increase of the Disp/Comb ratio.…”

“…The CTe Rr adicals ultimately combine to form the RTeÀTe Rd imer,w hereas the fate of the carbon-based radicals was investigated by NMR, SEC, and MS to quantify the respective contributions of Disp and Comb, see Scheme 1( Aa nd B). Furthermore, the generation of radicalst hroughp hotolysisa llowed these termination reactions to be investigated under aw ide variety of conditions by varying temperature and solvent.While the Disp/Comb ratio was as expected on the basis of previousl iterature reports for the pMMAC and pStC radicals, [6a] it was surprising to find that acrylate radicalsr esulting from a pMAÀTe Ph macroinitiatort erminate almost exclusively (99 %) through Disp, [6b] in contrast with several other previous [5, 7] and subsequent [8] reports.I nt he most recent contribution, [6c] it was shownt hat the product distribution depends on the reaction medium, ag reater viscosity resulting in an increase of the Disp/Combr atio. For example, 59 %D isp was observed for the methacrylate unimerm odel compound Me 2 C(TeMe)CO 2 Me at relativelyl ow viscosity (h = 1.1 mPas), whereas this amount increased significantly to 94 %a th = 84 mPas at room temperature.…”

“…While the Disp/Comb ratio was as expected on the basis of previousl iterature reports for the pMMAC and pStC radicals, [6a] it was surprising to find that acrylate radicalsr esulting from a pMAÀTe Ph macroinitiatort erminate almost exclusively (99 %) through Disp, [6b] in contrast with several other previous [5, 7] and subsequent [8] reports.I nt he most recent contribution, [6c] it was shownt hat the product distribution depends on the reaction medium, ag reater viscosity resulting in an increase of the Disp/Combr atio. For example, 59 %D isp was observed for the methacrylate unimerm odel compound Me 2 C(TeMe)CO 2 Me at relativelyl ow viscosity (h = 1.1 mPas), whereas this amount increased significantly to 94 %a th = 84 mPas at room temperature.…”

“…The DFT calculations support this view (see Table ). For polyacrylate radicals, the occurrence of transfer reactions such as backbiting must also be carefully considered …”

Fundamentals of chemical incorporation of ionic monomers onto polymer colloids: paving the way for surfactant-free waterborne dispersions

“…39 In this context, it is worth pointing out that it has recently been confirmed that the termination of secondary acrylates radicals occurs by combination. 40 If this is correct, the rate coefficient for intermolecular chain transfer to polymer should be higher than the previously estimated values. 39 Table 5.…”