Steric and Electronic Effects in Cyclic Alkoxyamines—Synthesis and Applications as Regulators for Controlled/Living Radical Polymerization

Abstract

The synthesis of new six- and seven-membered cyclic alkoxyamines bearing ethyl groups at the alpha-N position of the alkoxyamines is described. The key step in the synthesis of the sterically hindered six-membered cyclic alkoxyamines is a Wadsworth-Horner-Emmons olefination with bisphosphonate 1. The seven-membered cyclic alkoxyamines were prepared from the corresponding six-membered keto alkoxyamines by ring-enlargement with trimethylsilyl(TMS)-diazomethane. The use of the new alkoxyamines as regulators/initiators for radical polymerization is discussed. Efficient controlled and living polymerization of styrene and n-butyl acrylate was obtained with the six-membered tetraethyl alkoxyamine 13. Controlled polymerizations can be conducted even at 90 degrees C. In addition, alkoxyamine 13 can be used for the preparation of AB diblock and ABA triblock copolymers with narrow polydispersities. The influence of the replacement of methyl groups in the alpha-position of the N atom in cyclic alkoxyamines by larger ethyl groups on the styrene polymerization (reaction time, PDI, kinetics of the C-O bond homolysis) is discussed. In addition, thermal decomposition of the new alkoxyamines was studied. Furthermore, the synthesis of N,N-bissilylated alkoxyamines is described. The silylated alkoxyamines are not suitable as regulators/initiators for the controlled/living radical polymerization. The C-O bonds in silylated alkoxyamines are stronger than the C-O bonds in analogous N,N-dialkylated alkoxyamines. The experimental results are verified by calculations with Gaussian 98 (A. 9).

Site‐Selective Surface‐Initiated Polymerization by Langmuir–Blodgett Lithography

“…Alkoxy amine 5, which has a sterically more demanding nitroxide moiety, [16] was prepared in an analogous manner (see the Supporting Information). Compound 4 forms stable monolayers in a mixture with DPPC at the air/water interface.…”

“…Alkoxy amine 5 bears a nitroxide group, which is able to control acrylate polymerization. [16] LB lithography was performed with a mixed DPPC/5 monolayer containing 10 mol % 5. The regularity of stripe pattern improved significantly, indicating better compatibility of 5 with DPPC.…”

Synthesis and Reduction Kinetics of Five Ibuprofen–Nitroxides for Ascorbic Acid and Methyl Radicals

“…Due to the lipophilicity of the ibuprophen-nitroxides, nitroxide-radicals in compounds 2-5 were no detectable in PBS. Log P o/w of 1 was also 3 ) for 200-Folds Excess AsA The rates of reduction for nitroxides 1-5 were studied under pseudo-first-order conditions using a 200-fold excess of AsA in DMSO. Second-order rate constants, k were obtained by monitoring the decay of the low-field EPR peak height of nitroxides/peak height of the Mn marker from 2 min to 10 min after reaction at 295 K (Fig.…”

“…They had different reduction rates for reductants such as ascorbic acid (AsA), and these were applied as an invivo probe. [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17] The rate constant of reduction of a nitroxide probe in vitro is expected to be a guideline of its half-life in vivo. [9][10][11] The rate constants of them are greatly different and could not measure under the same conditions.…”

Synthesis and Utilization of α-Substituted Nitroxides

“…For example, Yoshioka et al reported on the synthesis for piperidine nitroxides having a spirocyclohexyl group via , -unsaturated ketone derivatives (Yoshioka et al, 1972). In addition, focusing on substitution of the tetraethyl group, Studer et al reported a stepwise synthesis via bisphosphonates (Wetter et al, 2004), and also -lactams for obtaining piperidine nitroxides on a large scale (Schulte et al, 2005) which involved several synthetic steps and a high-pressure reactor.…”