The effect of the size of the alkyl substituent on the catalysis of chain transfer to monomer in radical polymerization of n-alkyl methacrylates

The Effects of Ester Chain Length and Temperature on the Catalytic Chain Transfer Polymerization of Methacrylates

“…[1][2][3][4][5] This technique is based upon the property of certain low-spin Co(II) complexes to catalyze the chain transfer to monomer reaction (shown in Scheme 1 for the polymerization of methyl methacrylate). [1][2][3][6][7][8][9][10] It has been well-established that virtually all chains are initiated by a hydrogen atom and terminated by a vinyl end group, [6][7][8] but despite many efforts, [6][7][8][9][10][11][12][13][14][15][16][17][18][19] most notably those by Gridnev and coworkers [20][21][22][23][24][25][26][27] a fully consistent and unambiguous mechanism has not yet appeared.…”

“…In mechanistic studies, the Arrhenius parameters of the overall reaction rate coefficient provide very valuable information about the kinetics and character of the rate-determining step and the nature and importance of substituent effects (for example in a homologous series of monomers). To our knowledge, only three studies of the Arrhenius parameters 11,18,19 and one study of the catalytic chain transfer polymerization of a homologous series of methacrylates 13 have been published to date. In one study 18 a very strong temperature dependence of the catalytic chain transfer reaction in methyl methacrylate was reported.…”

Catalytic chain‐transfer synthesis of 1,1,2,2‐tetrahydroperfluoroalkyl methacrylate macromonomers

“…A plot of 1/DP n versus [CoBF]/[M] is linear and yields an apparent chain‐transfer constant of 110 ( r 2 =0.99). Although shorter chain hydrocarbon methacrylates exhibit very high chain‐transfer constants (i.e., methyl, 34,000; ethyl methacrylate, 26,000; and butyl methacrylate, 16,000),23 the value reported here is consistent with previous reports for long‐chain hydrocarbon methacrylates (i.e., nonyl methacrylate, 150; decyl methacrylate, 110; and hexadecyl methacrylate, 130) 34. Previous investigators attributed the observed decrease in the chain‐transfer constant with increasing ester chain length to steric effects, and although these results were generated with a slightly different catalyst, they provide a reasonable basis for comparison.…”

Catalytic chain transfer and its derived macromonomers

“…The Co III H complex then reacts with a monomer molecule yielding back the original Co II catalyst and a monomeric radical, which can start growing. This mechanism has been studied in detail [1][2][3][4][5][6][7][8][9][10][11][12]20,21,[23][24][25][26][27][28]57,60,65,67,82 and can be summarized in the catalytic cycle of Scheme 3. 1,27 In polymerization kinetic terms, the CCT process is just a chain transfer process with fast re-initiation and to a first approximation does not affect the rate of polymerization in any other way than do ordinary chain transfer agents (with the obvious exception of catalytic inhibition).…”