Summary: Plasma‐initiated controlled/living radical polymerization of methyl methacrylate (MMA) was carried out in the presence of 2‐cyanoprop‐2‐yl 1‐dithionaphthalate. Well‐defined poly(methyl methacrylate) (PMMA), with a narrow polydispersity, could be synthesized. The polymerization is proposed to occur via a RAFT mechanism. Chain‐extension reactions were also successfully carried out to obtain higher molecular weight PMMA and PMMA‐block‐PSt copolymer.
Dependence of ln([M]0/[M]) on post‐polymerization time (above), and \overline M _{\rm n} and PDI against conversion (below) for plasma initiated RAFT polymerization of MMA at 25 °C. 相似文献
The crosspropagation of 1‐ethylcyclopentyl methacrylate (ECPMA) and methyl methacrylate (MMA) has been studied using a combination of quantum chemistry calculations and experiment. Our computational work utilizes a trimer‐to‐tetramer reaction model, coupled with an ONIOM (B3LYP/6‐31G(2df,p): B3LYP/6‐31G(d)) method for geometry optimization and an M06‐2X/6‐311+G(2df,p) method plus SMD solvation model for single point energy calculations. The results show several trends: the identity of the ultimate unit of a trimer radical affects not only the preferred conformation of the region where the reaction takes place, but also the reactivity of the radical; the addition of an ECPMA monomer to the radicals is generally favored compared to an MMA monomer; the pen‐penultimate unit of a trimer radical shows a nonnegligible entropic effect; the penultimate unit effect is implicit for the ECPMA–MMA copolymer system. Finally, terminal model reactivity ratios fitted based on the explicit rate coefficients calculated from the quantum chemical results are compared with those from experimental measurements. The computations not only agree qualitatively with experimentally derived results in terms of the selectivity of ECPMA–MMA crosspropagation, but also give reasonable quantitative predictions of reactivity ratios.
Summary: Experimental and modeling studies of addition–fragmentation chain transfer (AFCT) during radical polymerization of methyl methacrylate in the presence of poly(methyl methacrylate) macromonomer with 2‐carbomethoxy‐2‐propenyl ω‐ends (PMMA‐CO2Me) at 60 °C are reported. The results revealed that AFCT involving PMMA‐CO2Me formed in situ during methyl methacrylate polymerization has a negligible effect on the molecular weight distribution.
CuYS2: A Ternary Copper(I) Yttrium(III) Sulfide with Chains {[Cu(S1)3/3(S2)1/1]3–} of cis ‐Edge Connected [CuS4]7– Tetrahedra Pale yellow, lath‐shaped single crystals of the ternary copper(I) yttrium(III) sulfide CuYS2 are obtained by the oxidation of equimolar mixtures of the metals (copper and yttrium) with sulfur in the molar ratio 1 : 1 : 2 within fourteen days at 900 °C in evacuated silica ampoules, while the presence of CsCl as fluxing agent promotes their growth. The crystal structure of CuYS2 (orthorhombic, Pnma; a = 1345.3(1), b = 398.12(4), c = 629.08(6) pm, Z = 4) exhibits chains of cis‐edge linked [CuS4]7– tetrahedra with the composition {[Cu(S1)3/3(S2)1/1]3–} running along [010] which are hexagonally bundled as closest rod packing. Charge equalization and three‐dimensional interconnection of these anionic chains occur via octahedrally coordinated Y3+ cations. These are forming together with the S2– anions a network [Y(S1)3/3(S2)3/3]– of vertex‐ and edge‐shared [YS6]9– octahedra with ramsdellite topology. The metall‐sulfur distances of the [CuS4]7– tetrahedra (230 (Cu–S2), 232 (Cu–S1), and 253 pm (Cu–S1′, 2 × )) cover a very broad interval, whilst these (Y–S: 267–280 pm) within the [YS6]9– octahedra range rather closely together. 相似文献
Kinetic measurements for the thermal rearrangement of 2,2‐diphenyl‐1‐[(E)‐styryl]cyclopropane ( 22a ) to 3,4,4‐triphenylcyclopent‐1‐ene ( 23a ) in decalin furnished ΔH =31.0±1.2 kcal mol?1 and ΔS =?6.0±2.6 e.u. The lowering of ΔH≠ by 20 kcal mol?1, compared with the rearrangement of the vinylcyclopropane parent, is ascribed to the stabilization of a transition structure (TS) with allylic diradical character. The racemization of (+)‐(S)‐ 22a proceeds with ΔH =28.2±0.8 kcal mol?1 and ΔS =?5±2 e.u., and is at 150° 106 times faster than the rearrangement. Seven further 1‐(2‐arylethenyl)‐2,2‐diphenylcyclopropanes 22 , (E)‐ and (Z)‐isomers, were synthesized and characterized. The (E)‐compounds showed only modest substituent influence in their krac (at 119.4°) and kisom (at 159.3°) values. The lack of solvent dependence of rate opposes charge separation in the TS, but a linear relation of log krac with log p.r.f., i.e., partial rate factors of radical phenylations of ArH, agrees with a diradical TS. The ring‐opening of the preponderant s‐trans‐conformation of 22 gives rise to the 1‐exo‐phenylallyl radical 26 that bears the diphenylethyl radical in 3‐exo‐position, and is responsible for racemization. The 1‐exo‐3‐endo‐substituted allylic diradical 27 arises from the minor s‐gauche‐conformation of 22 and is capable of closing the three‐ or the five‐membered ring, 22 or 23 , respectively. The discussion centers on the question whether the allylic diradical is an intermediate or merely a TS. Quantum‐chemical calculations by Houk et al. (1997) for the parent vinylcyclopropane reveal the lack of an intermediate. Can the conjugation of the allylic diradical with three Ph groups carve the well of an intermediate? 相似文献
This study presents the synthesis and characterization of zwitterionic core–shell hybrid nanoparticles consisting of a core of iron oxide multicore nanoparticles (MCNPs, γ‐Fe2O3) and a shell of sultonated poly(2‐vinylpyridine‐grad‐acrylic acid) copolymers. The gradient copolymers are prepared by reversible addition fragmentation chain transfer polymerization of 2‐vinylpyridine (2VP), followed by the addition of tert‐butyl acrylate and subsequent hydrolysis. Grafting of P(2VP‐grad‐AA) onto MCNP results in P(2VP‐grad‐AA)@MCNP, followed by quaternization using 1,3‐propanesultone—leading to P(2VPS‐grad‐AA)@MCNP with a zwitterionic shell. The resulting particles are characterized by transmission electron microscopy, dynamic light scattering, and thermogravimetric analysis measurements, showing particle diameters of ≈70–90 nm and an overall content of the copolymer shell of ≈10%. Turbidity measurements indicate increased stability toward secondary aggregation after coating if compared to the pristine MCNP and additional cytotoxicity tests do not reveal any significant influence on cell viability.
Tris(dimethylsilyl)methyl lithium, (HSiMe2)3CLi, reacts with allyl, phenyl, benzyl, n‐propyl and n‐butyl glycidyl ethers in THF at ‐5 °C to give 1‐oxa‐2‐silacyclopentane derivatives. It seems that ring closure is facilitated by conversion of the Si? H bond into an Si? O bond. Glycidyl methacrylate (GM) random copolymers with 4‐methyl‐ and 4‐methoxy styrene, synthesized by solution free radical polymerization at 70 (±1) °C with α,α‐azobis(isobutyronitrile) (AIBN) as initiator, contained pendant epoxide functions. Treatment of these with (HSiMe2)3CLi did not lead to intramolecular nucleophilic attack as found for simple epoxides. 相似文献
1,5‐Hydrogen transfer reactions in methyl acrylate and butyl acrylate free‐radical polymerization are studied using quantum chemistry and transition state theory to estimate the kinetic parameters (ktr, Ea, and A) with tetrameric radicals, requiring a number of atoms that ranks among the largest polymeric mimics to date. A two‐step transformation accounted for the overall reaction: rotation from an extended conformation to a coiled conformation and abstraction of the fifth hydrogen atom by the end‐chain radical. UB3LYP/6‐31G(d) was used for geometry optimization, validation of the transition states, and calculation of frequencies that were used to obtain thermodynamic properties. The more computationally demanding level of theory, MPWB1K/6‐31G(d,p), was used for calculation of the electronic energy.
A new copper catalyst containing chlorine and a photo‐labile diethylthiocarbamoylthiyl group was successfully employed in the reverse ATRP of methyl methacrylate (MMA). The polymeric chains were end‐capped with S2CNEt2, due to pseudo‐halogen atom‐transfer reaction between active and dormant species. Photopolymerization of this PMMA in the presence of fresh MMA and styrene monomers at ambient temperature yielded chain‐extended PMMA and MMA/styrene block copolymers, respectively.
GPC traces of (A) PMMA end‐capped with a photo‐labile group (pre‐PMMA), (B) chain‐extended PMMA (post‐PMMA), and (C) PMMA/styrene block copolymer (PMMA‐b‐PSt). 相似文献
Synthesis of 6‐bromo‐2‐(substituted)‐3‐(1‐phenyl‐ethyl)‐3,4‐dihydro‐1H‐isophosphinoline 2‐chalco‐genides derivatives (6) were synthesized from 2‐[(1‐phenylethylamino)methyl]‐4‐bromophenol ( 1 ) by reaction with aryl/alkyl phosphoro dichloridates ( 2 ) in the presence of triethylamine at 55°C to 60°C to obtained the title compounds ( 6a‐g ). The title compounds ( 6h‐j ), were prepared via intermediate route. Few other title compounds ( 8a‐c ) were accomplished through a two step synthetic route involving 1 with dichlorophenyl phosphine ( 2a ) and dichloroethyl phosphine ( 2a,b ) in the presence of triethylamine in dry toluene under N2 atmosphere to form the corresponding trivalent phosphorus intermediate (7) . In the second step they were further converted to the corresponding chalcogenides 8a‐c by reaction with hydrogen peroxide, sulfur and selenium respectively. They exhibited significant antibacterial, fungal and insecticidal activity. 相似文献
A series of N‐(3‐amino‐3,4‐dihydro‐4‐oxopyrimidin‐2‐yl)‐4‐chloro‐2‐mercapto‐5‐methylbenzenesulfonamide derivatives 10‐17 have been synthesized as potential anti‐HIV agents. The in vitro anti‐HIV‐1 activity of these compounds has been tested at the national Cancer Institute (Bethesda, MD), and the structure‐activity relationships are discussed. The selected N‐[3‐amino‐3,4‐dihydro‐6‐(tert‐butyl)‐4‐oxothieno[2,3‐e]pyrimidin‐2‐yl]‐4‐chloro‐2‐metcapto‐5‐methylbenzenesulfonamide ( 14 ) showed good anti‐HIV‐1 activity with 50% effective concentration (EC50) value of 15 μM and weak cytotoxic effect (IC50 = 106 μM). 相似文献
Lignin‐grafted copolymers, namely lignin‐graft‐poly(methyl methacrylate‐co‐butyl acrylate) (lignin‐g‐P(MMA‐co‐BA)), are synthesized via “grafting from” atom transfer radical polymerization (ATRP) with the aid of lignin‐based macroinitiators. By manipulating the monomer feed ratios of MMA/BA, grafted copolymers with tunable glass transition temperatures (−10–40 °C) are obtained. These copolymers are evaluated as sustainable thermoplastic elastomers (TPEs). The results suggest that the mechanical properties of these TPEs lignin‐g‐P(MMA‐co‐BA) copolymers are improved significantly by comparing with those of linear P(MMA‐co‐BA) copolymer counterparts, and the elastic strain recovery is nearly 70%. Lignin‐g‐P(MMA‐co‐BA) copolymers exhibit high absorption in the range of the UV spectrum, which might allow for applications in UV‐blocking coatings.
A number of 4‐aryloxymethyl‐6‐phenyl‐2H‐pyrano[3,2‐c][1,8]naphthyridin‐5(6H)‐ones ( 4a‐f ) are regioselectively synthesized in 72‐78% yield by the Claisen rearrangement of 4‐(4′‐aryloxybut‐2′‐ynyloxy)‐1‐phenyl‐1,8‐naphthyridin‐2(1H)‐ones ( 3a‐f ) in refluxing chlorobenzene for 4‐6 h. These products are then subjected to a second Claisen rearrangement catalyzed by anhydrous AlCl3 at room temperature for 2 h to give hitherto unreported pentacyclic heterocycles ( 5a‐f ) in 78‐85% yield. 相似文献
Economical atoms : 2‐Cyclopenten‐1‐ones, 5‐alkylidenefuran‐2(5 H)‐ones and indan‐1‐ones have been synthesized by atom‐economic reductive cyclocarbonylation of internal alkynes with carbon monoxide catalyzed by [{RhCl(CO)2}2]/CO(NH2)2 in the presence of water (see scheme).