Shining a light on catalytic chain transfer

Abstract

The catalytic chain transfer polymerization of styrene is only truly effective when the reaction mixture is exposed to (UV‐)light. The apparent chain transfer constant depends inversely on radical concentration and can be increased up to 8000. These results can be explained by combining aspects of both catalytic chain transfer and the formation of cobalt‐carbon bonds. For the catalytic chain transfer polymerization of n‐butyl acrylate a chain transfer constant of 650 was found. The resulting transfer coefficient has the same order of magnitude as the one for n‐butyl methacrylate. This means that the absence of an α‐methyl group hardly influences the transfer step itself. Furthermore, the effect of possible impurities on the catalytic chain transfer polymerization of methyl methacrylate is investigated.

Solvent Effects, Diffusion Control and Mechanistic Aspects of Catalytic Chain Transfer Polymerization

“…[11] We performed experiments for different methacrylates in solution as well, and will compare our results with theoretical calculations for different levels of diffusion control, and also with results reported by Heuts et al [17][18][19] and by Roberts et al [20] A final point for discussion is the possible effect of the formation of covalent bonds between the polymeric radical and the cobalt complex, as has been reported in CCT polymerizations with e.g. acrylates, [7,21,22] styrene [23][24][25] and maleic anhydride. [22] When cobalt-carbon bond formation occurs, the amount of Co complex available for chain transfer decreases and only an apparent C T can be determined.…”

“…Theoretical Calculations for C T In order to make meaningful calculations for C T , valid estimates of the rate coefficients in Equation 23 have to be made. These rate coefficients are not generally available.…”

“…However, one must realize that when diffusion control does occur, this decrease in C T is counteracted. [57] Experimentally Observed Effects of Initiator Concentration on C T In order to relate the experimental observations to Equation 23, a relation between radical and initiator concentration is required. The total radical concentration can be expressed according to normal free-radical polymerization kinetics as [59] ½P ¼…”

Catalytic Chain Transfer Copolymerization of Methyl Methacrylate and Butyl Acrylate

“…Recently, we reported k tr,MMA ¼ 3.3 Â 10 7 LÁ mol À1 Á s À1 [37] and k tr,BA ¼ 2.2 Â 10 7 L Á mol À1 Á s À1 . [38] The order of magnitude of the estimates for K cd [P.] is based on a value of 2.4 Â 10 9 L Á mol À1 for a similar equilibrium between PMA. and tetramesitylporphyrinatocobalt(II) at 50 8C [27] and a radical concentration range of 10 À7 to 10 À9 mol Á L À1 .…”

Synthesis of Macromonomers via Catalytic Chain Transfer (CCT) Polymerization and their Characterization via NMR Spectroscopy and Electrospray Ionization Mass Spectrometry (ESI‐MS)

“…Monomers such as the acrylates and styrene also undergo CCT, but their apparent chain transfer constants are much lower because of a lowering of the effective catalyst concentration due to Co-C bond formation. [6][7][8][9][10][11][12][13] Furthermore, the resulting vinyl end functionality is less reactive Summary: Macromonomers consisting of a butyl acrylate (BA) tail and a-methyl styrene (AMS) or benzyl methacrylate (BzMA) unsaturated termini were synthesized via catalytic chain transfer (CCT) polymerization employing the low spin bis(difluoroboryl)dimethylglyoximato cobalt (II) (COBF) complex. The structures of the generated macromonomers were characterized via 1 H and 13 C NMR spectroscopy and electrospray ionization mass spectrometry (ESI-MS).…”