Fluorinated polymers are important materials that are widely used in many areas as taking the advantage of inertness to chemical corrosion, prominent weather resistance, low flammability, and good thermal stability. Poly(vinylidene fluoride)(PVDF) based fluoropolymers is the most common type of commercial fluoropolymer especially used as dielectric materials. However, there are always some shortcomings in practical applications, so it is necessary to modify PVDF-based fluoropolymers for better a... 相似文献
Summary: Atom transfer radical polymerization (ATRP) and reversible addition‐fragmentation transfer (RAFT) polymerization of N‐methyl methacrylamide and methyl methacrylate were investigated in the presence of rare‐earth triflates known to enhance polymer isotacticity. Poly(N‐methyl methacrylamide) with controlled molecular weight, low polydispersity, and enhanced isotacticity was prepared by ATRP and RAFT in the presence of catalytic amounts of yttrium trifluoromethanesulfonate or ytterbium trifluoromethanesulfonate. The tacticity of poly(N‐methyl methacrylamide) depends on the Lewis acid concentration: well‐defined polymers with predominantly either syndiotactic, atactic, or isotactic triads were prepared by adjusting the concentration of the Lewis acid. Simultaneous control of molecular weights, polydispersities, and tacticities in the polymerization of methyl methacrylate was less successful.
Free radical propagation in the presence of a Lewis acid (LA) giving rise to chelate control. 相似文献
Well‐controlled radical polymerization of methyl methacrylate can be achieved by in situ photochemical generation of copper (I) complex from air‐stable copper (II) species without using any reducing agent at room temperature. The living character of this polymerization was confirmed by both the linear tendency of molecular weight evolution with conversion and a chain extension experiment.
We report first results on the controlled radical polymerization of 2,3‐epithiopropyl methacrylate (ETMA) also known as thiiran‐2‐ylmethyl methacrylate. Reversible addition‐fragmentation chain transfer (RAFT) of ETMA was carried out in bulk and in solution, using AIBN as initiator and the chain transfer agents: cyanopropyl dithiobenzoate (CPDB) and cumyl dithiobenzoate (CDB). A linear increase of the number‐average molecular weight and decrease of the polydispersity with monomer conversion were observed using CPDB as transfer agent, indicating a controlled process. Atom transfer radical polymerization (ATRP) of ETMA was performed under different reaction conditions using copper bromide complexed by tertiary amine ligands and ethyl 2‐bromoisobutyrate (EBiB) or 2‐bromopropionitrile (BPN) as initiator. All experiments lead to a crosslinked polymer. Preliminary studies in the absence of initiator showed that the CuBr/ligand complex alone initiates the ring‐opening polymerization of thiirane leading to a poly(propylene sulfide) with pendant methacrylate groups.
Electron spin resonance (ESR) spectroscopy can contribute to understanding both the kinetics and mechanism of radical polymerizations. A series of oligo/poly(meth)acrylates were prepared by atom transfer radical polymerization (ATRP) and purified to provide well defined radical precursors. Model radicals, with given chain lengths, were generated by reaction of the terminal halogens with an organotin compound and the radicals were observed by ESR spectroscopy. This combination of ESR with ATRPs ability to prepare well defined radical precursors provided significant new information on the properties of radicals in radical polymerizations. ESR spectra of the model radicals generated from tert-butyl methacrylate precursors, with various chain lengths, showed clear chain length dependent changes and a possibility of differentiating between the chain lengths of observed propagating radicals by ESR. The ESR spectrum of each dimeric, trimeric, tetrameric, and pentameric tert-butyl acrylate model radicals, observed at various temperatures, provided clear experimental evidence of a 1,5-hydrogen shift. 相似文献
Summary: Means of improving rates in RAFT‐mediated radical emulsion polymerizations are developed, by setting out strategies to minimize the inhibition and retardation that always are present in these systems. These effects arise from the RAFT‐induced exit of radicals, the desorption of the RAFT‐reinitiating radical from the particles, and the specificity of the reinitiating radical to the RAFT agent. Methods for reducing the inhibition period such as using a more hydrophobic reinitiating radical are predicted to show a significant improvement in the inhibition periods. The time‐dependent behavior of the RAFT adduct to the entering radical and the RAFT‐induced exit (loss) of radicals from particles are studied using a previously described Monte Carlo model of RAFT/emulsion particles. It is shown that an effective way of reducing the rate coefficient for the exit of radicals from the particles is to use a less active RAFT agent. Techniques for improving the rate of polymerization of RAFT/emulsion systems are suggested based upon the coherent understanding contained in these models: the use of an oligomeric adduct to the RAFT agent, a less water‐soluble RAFT re‐initiating group, and a less active RAFT agent.
Populations of the different types of particles (left axis) along with the concentration of the initial RAFT agent, DR (right axis), as a function of time. 相似文献
Atom transfer radical polymerization provides a new method of controlled radical polymerization. The most important advantage of ATRP is that it is tolerant to the different functional groups present in the initiator as well as in the monomer. Furfuryl Methacrylate (FMA) is a specialty monomer, which has applications in coatings, adhesives and in biomedicals. Conventional radical polymerization of FMA leads to excessive gel formation, which limits its applications. In this investigation homo and co-polymerization of FMA has been carried out via ATRP. ATRP of FMA was carried out using CuBr as catalyst and 1, 1, 4, 7, 10, 10 hexamethyltriethylenetetramine (HMTETA) as ligand. There was no gel formation during the polymerization. ATRP of FMA was well controlled with a linear increase of molecular weight (Mn) with monomer conversion. The polymers were characterized by using 1HNMR, FT-IR and GPC analysis. Interestingly, it was observed that the furfuryl ring was not affected during polymerization. 相似文献
A rapid oxygen‐initiated and ‐regulated controlled radical polymerization was conducted under ambient temperature and atmosphere. The reaction between triethylborane and oxygen provides ethyl radicals, which initiate and mediate the radical polymerization. The controlled radical polymerization was achieved using RAFT chain transfer agents (CTA) without any process of removing oxygen, providing well‐defined polymers with almost full conversion (>95 %) in a short period (15 min). High‐throughput screening was used to discover the suitable conditions for various CTA and monomers. To show the versatility of this method, a polymer library containing 25 well‐defined polymers with different compositions (block and statistical copolymers) and molecular weights were synthesized in 1 h via high‐throughput synthesis technique. A polymer‐painting technique was developed using this method, forming films with spatial control and excellent control in molecular weight and dispersity. 相似文献
Molecular oxygen is a radical scavenger in both conventional and controlled radical polymerization(CRP), resulting in many time-consuming methods for physically removing oxygen before the polymerization. Different approaches have been developed to have oxygen tolerance by chemically consuming or converting molecular oxygen into non-initiating species to address this issue. Recently, we propose another approach called oxygen initiation that directly transforms molecular oxygen into the initiating... 相似文献
Summary: Poly(N-vinylpyrrolidone) (PNVP) was polymerized by RAFT process using diphenyldithiocarbamate of diethylmalonate (DPCM) as the reversible chain transfer agent in the presence of a small percentage of a conventional radical initiator (AIBN). The molar mass of the polymers synthesized by this method was found to increase with conversion and time. The presence of end group in the polymer chain could be confirmed by 1H NMR spectra. The molar masses calculated using 1H NMR spectroscopy and static light scattering (SLS) showed good agreement with the theoretical molar masses. The RAFT compound was fully consumed during the initial stages of the polymerization itself. The controlled nature of these polymers was further confirmed by generating diblock copolymers by sequential addition of monomers such as styrene or n-butyl acrylate (n-BA). PNVP efficiently participated as a macro-RAFT reagent, and cross-over reaction between the two blocks efficiently occurred. The successful diblock copolymer synthesis using PNVP as macro-transfer reagent further confirms the “controlled” nature of such synthetic procedure. 相似文献
