Bifunctional alkoxyamine bis-TIPNO derived from 2,2,5-trimethyl-4-phenyl-3-azahexane-3-oxyl (TIPNO) and α, ω-alkyl bromide by atom transfer radical addition(ATRA) was employed as “biradical initiator” for nitroxide-mediated radical polymerization(NMRP) of isoprene and styrene. The kinetics study for the polymerization of styrene at different time showed living features. The poly(styrene-b-isoprene-b-styrene) (SIS) copolymers have two glass transition temperatures, indicating the immiscibility of the corresponding blocks. 相似文献
Summary: A low‐molar‐mass poly(acrylic acid) with a narrow molar‐mass distribution, prepared by SG1 nitroxide‐mediated controlled free‐radical polymerization, was subjected to end‐group analysis to confirm its living nature. 1H and 31P NMR spectroscopy confirmed the presence of the SG1‐based alkoxyamine end group. Furthermore, chain extension with styrene and n‐butyl acrylate demonstrated the ability of the homopolymer to initiate the polymerization of a second block. These results open the door to the synthesis of poly(acrylic acid)‐based block copolymers by direct nitroxide‐mediated polymerization of acrylic acid.
Acrylic acid polymerization using an alkoxyamine initiator based on SG1 (N‐tert‐butyl‐N‐(1‐diethyl phosphono‐2,2‐dimethylpropyl) nitroxide resulting in a homopolymer capable of initiating the polymerization of a second block. 相似文献
Eight (15)N-labeled derivatives of 1-ethoxy-2,2,6,6-tetramethylpiperidine were synthesized in order to investigate the effects of their structural units on (15)N NMR spectra. A single peak is found for each alkoxyamine. The chemical shift depends extensively on the nature of the alpha carbon atom of the alkoxy group. The remote functional group attached to position 4 of the piperidine ring has a smaller but still significant effect. The results of the (15)N NMR measurements are supported by the detection of the N-H and N-C spin-spin coupling from the (1)H and (13)C NMR. The investigated alkoxyamines are model compounds for the radical-trapping products of styryl, methyl methacryloyl, alpha-methylstyryl, and methyl acryloyl radicals by (15)N-labeled nitroxides. The potential of (15)N NMR spectroscopy to analyze such products is discussed. In addition, it is shown that the (13)C chemical shifts of the alpha carbon atom of the alkoxy group fall in an empty part of the (13)C NMR spectrum, which allows the identification of trapped (macro)radicals via natural abundance (13)C NMR. 相似文献
The kinetics of the free-radical polymerization of styrene at 120°C in the presence of alkoxyamine as a living polymerization agent has been studied. The alkoxyamine forms in situ with a 100-fold variation in the initial concentration of 2,2,6,6-tetramethyl-1-piperidinyloxy. The rate of the process at the stationary stage decreases with an increase in the initial concentration of 2,2,6,6-tetramethyl-1-piperidinyloxy. The computer simulation of the kinetic features of the process under study demonstrates that this tendency is related to the possible secondary inhibition of the process by alkoxyamine and/or hydroxylamine arising in the system in the course of polymerization. 相似文献
Polystyrenes containing fluorescence end-groups were prepared by nitroxide-mediated radical polymerization. Combined molar mass regulator contained besides alkoxyamine part the structure of fluorescence mark. Stable nitroxyl radical represented 2,2,6,6-tetramethylpiperidine-Noxyl and covalently bonded fluorescence mark was benzothioxanthene. A fluorescence method as well as UV absorption was employed for measuring the concentration of nitroxyl-terminated chains in polystyrene samples. Theoretical molar masses of polystyrenes were calculated from these concentrations on the assumption that all polystyrene chains are terminated by alkoxyamine dormant end-functionality bearing fluorescence probe. Comparisons of these data with the molar masses from GPC gave us the range of the marked active polymer chain ends. Fractions of active polymer chain ends depended on the conversion. With increased conversion the fraction of polystyrene chains terminated by alkoxyamine was decreased. From this follows that the “livingness” of polymerization process decreased with the increasing of conversion. It should result in higher extent of termination and subsequently in the increasing of polydispersity with increased conversion. Despite this the observed polydispersity was the same for all conversion and reached the value ca. 1.3. The changing viscosity is responsible for the constant polydispersity. 相似文献
Direct esterification of a labile alkoxyamine R1R2NOR3, which was previously reported as unsuccessful, is achieved by a Mitsunobu reaction or a nucleophilic substitution. Ester derivatives are obtained under smooth conditions and easily purified. Macrocyclization attempts on ester derivatives were successful for five-membered ring lactones and unsuccessful for 13-membered ring lactones. Moreover, the success of the cyclization was dramatically dependent on the quality of the solution degassing. Poor degassing led to unexpected carbonate alkoxyamine. 相似文献
Various C-centered radicals can efficiently be generated through thermal C-O-bond homolysis of alkoxyamines. This method is used to perform environmentally benign radical cyclization and intermolecular addition reactions. These alkoxyamine isomerizations and intermolecular carboaminoxylations are mediated by the persistent radical effect (PRE). In the paper, the effect of the variation of the alkoxyamine structure--in particular steric effects in the nitroxide moiety--on the outcome of the PRE mediated radical reactions will be discussed. Fourteen different nitroxides were used in the studies. It will be shown that reaction times can be shortened about 100 times upon careful tuning of the alkoxyamine structure. Activation energies for the C-O-bond homolysis of the various alkoxyamines are provided. The kinetic data are used to explain the reaction outcome of the PRE-mediated processes. 相似文献
The role of the alkyl fragment of alkoxyamine initiating the homopolymerization of styrene is experimentally and theoretically studied in the case of 2,2,6,6-tetramethylpiperidine-1-oxyl derivatives. The rate constants of homolysis and recombination are measured for the alkoxyamines under study. The characteristics of polymerization initiated by these compounds are experimentally examined. The kinetics of polymerization is theoretically calculated with allowance for the measured kinetic parameters and the experimentally detected side reaction of hydrogen-atom transfer to the nitroxide radical during the thermolysis of alkoxyamine 2-cyano-2-isopropyl-TEMPO. 相似文献
Summary: This study examined the kinetics of nitroxide-mediated radical polymerization of styrene with unimolecular (alkoxyamine) initiators. Control of polymerization rate and polymer molecular weight in unimolecular nitroxide-mediated radical polymerization was studied by looking at the effects of the three main factors: initiator concentration, temperature, and initiator molecular weight on polymerization rate, molecular weight and polydispersity. In addition, the behavior of the unimolecular initiating systems was compared to that of the corresponding bimolecular system. The effective TEMPO concentration and degree of self-initiation of styrene were proved to be significant in dictating magnitudes of molecular weight averages and widths of molecular weight distribution. 相似文献