A TEMPO bromide salt is used to functionalize a silica surface with nitroxyl moieties. The functionalization reaction takes place in 48 h under mild conditions. In a second step, grafts of styrene‐maleic anhydride copolymer are grown from the functionalized silica surface by heating it in the presence of the monomers. FT‐IR and TGA analysis show that the silica was first functionalized with nitroxide moieties, and then that grafts of styrene‐maleic anhydride grew from the functionalized silica surface. A reaction mechanism is proposed in order to explain the findings. The results suggest that the oxoaminium salts are good candidates for the functionalization and grafting of surfaces that contain hydroxy groups and for the generation of hybrid materials with improved properties.
The N,N′-diaminoethane linked bis-TEMPO nitroxide (C2)-mediated free radical polymerization of styrene at 135 °C in bulk was studied. It was found that under comparable conditions a single nitroxide group of C2 biradical retards the polymerization more than TEMPO. The results were discussed in terms of through-space interactions between two TEMPO moieties of C2 biradical and diffusion effects. According to experimental results analyzed by means of statistical methods, the polymerization system displays a bimodal molecular-weight distribution (MWD) from the beginning of the polymerization process, most probably by undergoing decomposition side reactions leading to irreversible polymer arm (P) separation from PC2P to PC2 and PC2H alkoxyamines. The scale of the decomposition depends rather on the time the system is maintained at the polymerization temperature than on conversion of monomer. Generally, the contribution of low molecular weight chains to overall MWD increases with time of polymerization whereas the contribution of high molecular weight chains to MWD increases for less controlled polymerization systems. For polymers obtained at high [dinitroxide]/[initiator] ratio, the thermal treatment of polystyrene in mass at 135 °C unexpectedly revealed an increase of Mn, which can probably be ascribed to post-polymerization effects involving polystyrene with unsaturated chains end groups. 相似文献
This study shows that reasonably controlled nitroxide-mediated polymerization of acrylamide is achieved in pure water solution at 120 °C and high concentration (40 wt%), using a combination of a conventional hydrosoluble radical initiator (Vazo56) and a β-phosphonylated nitroxide, SG1. Moreover, some chain extensions can be performed from a polyacrylamide macroinitiator. Under these experimental conditions, we have demonstrated the conservation of the acrylamide structure without hydrolysis side reactions. The physico-chemical characterizations of polymers obtained from this method demonstrates that the controlled growing chain arises as a star-like shape from the hydrophobic core composed of SG1-functionalized polyacrylamide in the presence of a slight excess of SG1. 相似文献
In this work, the incorporation of a 2,2,6,6‐tetramethylpiperydinyl‐1‐oxyl (TEMPO) group to a benzoxazine ring is performed using a one‐pot synthesis for the preparation of TEMPO‐functionalized benzoxazine compounds and polymers as reactive and crosslinkable initiators for nitroxide‐mediated polymerization (NMP). The TEMPO‐functionalization reaction of benzoxazine, traced with 1H NMR, is conducted with sequential radical transfer and coupling reactions. Moreover, polystyrene‐grafted polybenzoxazine copolymers are prepared with the TEMPO‐benzoxazine initiator and NMP of styrene. The polymerization system exhibits the characteristics of controlled radical polymerization, including controlled molecular weights of products and ability for sequential polymerization. Moreover, based on the chemical reactivity and crosslinking ability of benzoxazine groups, the synthesis route developed in this work will widen the scope of the design and synthesis of functional and high‐performance polymers.
Living radical polymerizations of acrylate are known to be difficult to achieve using TEMPO as a mediator. The stable free radical polymerization (SFRP) of acrylate tends to stop at low monomer conversion due to the accumulation of TEMPO in the medium as a result of unavoidable bimolecular termination. Rather than solving this problem by destroying the excess nitroxide using ascorbic acid or glyceraldehyde associated with pyridine as reported recently, high temperature initiators were used to slowly and continuously generate new radicals throughout the polymerization to consume the excess TEMPO molecules. Polymerizations of n-butyl acrylate initiated by the alkoxyamine unimer (1-benzoyloxy)-2-phenyl-2-(2′,2′,6′,6′-tetramethyl-1′-piperidinyloxy)ethane (BST) were performed between 130 °C and 134 °C in the presence of a series of high temperature peroxide and azo initiators. The best results in this study were obtained by the continuous addition of small amounts of di-tert-amyl peroxide throughout the polymerization. Under these conditions, the acrylate polymerizations fulfilled the criteria of a controlled polymerization process although the molecular weight distributions were slightly broad (Mw/Mn ∼ 1.5). 相似文献
Multiwalled carbon nanotubes (MWCNT) were grafted with polystyrene by in situ nitroxide mediated radical polymerization in the presence of TEMPO (2,2,6,6-tetramethylpiperidinyl-1-oxyl) functionalized MWCNT, which was synthesized by the reaction between 4-hydroxyl-TEMPO (HO-TEMPO) and carbonyl chloride groups on the MWCNT. Although the controllability of the polymerization was not high, highly soluble grafted MWCNTs were indeed obtained, indicating that the graft polymerization was efficient. The resulting polystyrene grafted MWCNTs were easily defunctionalized at room temperature using 3-chloroperoxybenzioc acid. TEM, SEM, and TGA were employed to determine the structure, morphology, and the grafting quantities of the resulting products. 相似文献
A functionalized compound, 4‐(2‐bromoisobutyryl)‐2,2,6,6‐tetra‐methylpiperidine‐1‐oxyl (Br‐TEMPO), was synthesized and used to synthesize block copolymers through tandem nitroxide‐mediated radical polymerization (NMRP) and atom transfer radical polymerization (ATRP). First, Br‐TEMPO was used to mediate the polymerization of styrene. The kinetics of polymerization proved a typical “living” nature of the reaction and the effectiveness in the mediation of polymerization of Br‐TEMPO. Then the PS‐Br macroinitiator was used to initiate atom transfer radical polymerization (ATRP). A series of acrylates were initiated by PS‐Br macroinitiators in typical ATRP processes at various conditions. The controlled polymerization of ATRP was also confirmed by molecular weight and kinetic analysis. Several cleavable block copolymers of PS‐b‐P(t‐BA), PS‐b‐P(n‐BA), and PS‐b‐PMA, with different molecular weights, were synthesized via this strategy. Relatively low polydispersities (<1.5) were observed and the molecular weights were in agreement with the theoretical ones. Hydrolysis of PS‐b‐P(t‐BA) was carried out, giving amphiphilic block copolymer PS‐b‐PAA without the cleavage of C‐ON bond or ester bond. All the block copolymers have two Tgs as demonstrated by DSC. A typical cleavable block copolymer of PS‐b‐PMA was cleaved by adding phenylhydrazine at 120°C to produce homopolymers in situ. 相似文献
The nature of plasmon interaction with organic molecules is a subject of fierce discussion about thermal and non-thermal effects. Despite the abundance of physical methods for evaluating the plasmonic effects, chemical insight has not been reported yet. In this contribution, we propose a chemical insight into the plasmon effect on reaction kinetics using alkoxyamines as an organic probe through their homolysis, leading to the generation of nitroxide radicals. Alkoxyamines (TEMPO- and SG1-substituted) with well-studied homolysis behavior are covalently attached to spherical Au nanoparticles. We evaluate the kinetic parameters of homolysis of alkoxyamines attached on a plasmon-active surface under heating and irradiation at a wavelength of plasmon resonance. The estimation of kinetic parameters from experiments with different probes (Au–TEMPO, Au–SG1, Au–SG1–TEMPO) allows revealing the apparent differences associated with the non-thermal contribution of plasmon activation. Moreover, our findings underline the dependency of kinetic parameters on the structure of organic molecules, which highlights the necessity to consider the nature of organic transformations and molecular structure in plasmon catalysis.Kinetic study of alkoxyamine homolysis revealed the impact of non-thermal effects in plasmon-assisted reactions.相似文献
Spruce sulphite cellulose (number average degree of polymerization 620) dissolved in an aqueous solution of 8% (w/w) LiOH*H2O and 12% (w/w) urea was methylated with dimethyl sulphate (DMS). By varying the reaction temperature between 22 and 50 °C, the molar ratio between 9 and 15 mol DMS per mol anhydroglucose unit, and the reaction time from 4 to 24 h, methyl cellulose (MC) with degree of substitution (DS) values in the range of 1.07 and 1.59 was prepared. The chemical structure of MC was analysed by FTIR and 1H NMR spectroscopy. The turbidity (given in nephelometric turbidity units, NTU) of the aqueous solution of MC reached an optimum of 10 NTU for a product obtained with 12 mol DMS/mol AGU at 50 °C. GPC measurements revealed polymer degradation to a certain extent. The intrinsic viscosity and the Huggins constant k of the MC samples increased with increasing DS value. The MC samples possess k values higher than 0.8, indicating association of the polymer chain. The zero-shear viscosity decreased with increase of both temperature and the amount of methylation agent due to the depolymerization. During the heating/cooling cycle (20-90 °C) of the aqueous solutions of MC, it was observed that samples synthesized at 22 °C with DS values lower than 1.3 did not undergo phase separation in aqueous solution. Phase separation hysteresis with a precipitation temperature up to 80 °C was obtained for aqueous solutions of MC with DS values between 1.07 and 1.66 synthesized at higher temperatures. The functionalization pattern determined by GLC of the corresponding partially methylated glucitol acetates is close to randomness and comparable with those of commercial MC samples. 相似文献