Ionic species in poly(methyl methacrylate) (PMMA) have been studied by optical absorption and ESR spectrometry. γ-Irradiation of PMMA containing aromatic solutes gave rise to the absorption spectra of corresponding cation radicals. The G value for the formation of cation radicals was determined to be 1.5. Anionic radicals of the solutes were not detected for the aromatic solutes studied. Anionic species of pure PMMA were identified by both absorption spectra and ESR spectra. It has an absorption maximum at 440 nm. A sharp singlet with a line width of about 5 G which was found by ESR spectrometry was tentatively assigned to the trapped electron of PMMA. The results show that a large number of electron traps in PMMA may exist on the ester side chain themselves. 相似文献
Threshold photoelectron-photoion coincidence (TPEPICO) spectroscopy has been used to investigate the unimolecular chemistry of gas-phase methyl 2-methyl butanoate ions [CH3CH2CH(CH3)COOCH3·+]. This ester ion isomerizes to a lower energy distonic ion [CH2CH2CH(CH3)COHOCH3·+] prior to dissociating by the loss of C2H4. The asymmetric time of flight distributions, which arise from the slow rate of dissociation at low ion energies, provide information about the ion dissociation rates. By modeling these rates with assumed k(E) functions, the thermal energy distribution for room temperature sample, and the analyzer function for threshold electrons, it was possible to extract the dissociative photoionization threshold for methyl 2-methyl butanoate which at 0 K is 9.80 ± 0.01 eV as well as the dissociation barrier of the distonic ion of 0.86 ± 0.01 eV. By combining these with an estimated heat of formation of methyl 2-methyl butanoate, we derive a 0 K heat of formation of the distonic ion CH2CH2CH(CH3)COHOCH3·+ of 101.0 ± 2.0 kcal/mol. The product ion is the enol of methyl propionate, CH3CHCOHOCH3·+, which has a derived heat of formation at 0 K of 106.0 ± 2.0 kcal/mol. 相似文献
Single crystals of dimethyl disulfide and methane thiol were irradiated at 77°K. CH3S radicals were produced in both compounds and measurement of the isotropic coupling constant from the methyl protons gave a value of 7.6 G. In the dimethyl disulfide crystal both the anion, CH3SSCH3, and the cation, CH3SSCH+3, radicals were observed. The disulfide anion radical exhibited an isotropic septet of lines with a = 5.0 G. Comparison with measurements on a polycrystalline sample gave g⊥ = 2.020 and g6 = 2.000 for this radical. The disulfide cation radical exhibited an evenly spaced septet of lines with a = 9.1 G and a maximum value for the g factor of 2.032.On illumination with IR radiation (λ > 590 mm) the disulfide cation radicals were easily bleached together with about 50% of the disulfide anion radicals suggesting a photoinduced neutralization process. The presence of weak 33S satellite lines in the anion radical spectrum indicates that 12% of the unpaired spin is localized to the two sulfur 3s orbitals. The structure of the disulfide cation radical is discussed in relation to earlier studies and a dihedral angle of 180° is proposed. The mechanisms for radical formation and decay in dimethyl disulfide and methane thiol are also discussed. 相似文献
Analysis of ESR spectra of mechanoradicals from poly(methyl methacrylate) reveals that after mechanical degradation in vacuo at 77°K, the sample contains two types of primary radicals? CH2? C(CH3)(COOCH3) (I) and CH2? C(CH3)(COOCH3)? CH2 (II) produced by the breaking of the polymer chain, and secondary radicals ? CH2? C(CH3)(COOCH3)? CH? C(CH3)? (COOCH3)? CH2? (III). With increasing temperature, radical I remains stable while II reacts with methylene hydrogen of the polymer chain giving rise to the secondary radical III, which decays and finally disappears as the temperature rises. After admission of oxygen at 113°K, the polymer radicals react with oxygen with formation of polymer peroxy radicals ROO. and diamagnetic dimers. With increasing temperature the latter dissociate again to the original polymer peroxy radicals which gradually decay, if the temperature is increased further. The present results are compared with earlier ones obtained on poly(ethylene glycol methacrylate) (PGMA). 相似文献
The radical anion and the radical cation of azuleno[1,2,3-cd]phenalene (III) have been investigated by ESR. spectroscopy, along with the radical anion of 2-phenylazulene (IV). Also studied has been the neutral radical obtained by one-electron reduction of cyclohepta[cd]phenalenium-cation (VI⊕). Assignment of the proton coupling constants for the radical ions III. ·?, III ·⊕ and IV·⊕, and the radical VI · is supported by comparison with the ESR. spectra of specifically deuteriated derivatives III-d5 ·?, III-d5 ·⊕, IV-d2 ·? and VI-d1′. The experimental results are in full accord with qualitative topological arguments and predictions of HMO models. Whereas the radical anion III ·? exhibits α-spin distribution similar to that of IV ·?the corresponding radical cation III ·⊕ and the neutral radical VI · are related in this respect to phenalenyl (V·). It is noteworthy that oxidation of III by conc. H2SO4 yields a paramagnetic species (IIIa ·⊕) which has a similar – but not an identical – structure as the radical cation III ·⊕ produced from III with AlCl3 in CH3NO2. 相似文献
The mechanism of uv (λ > 325 nm) photodegradation of polypropylene (PP) containing N,N,N′,N′-tetramethyl-p-phenylenediamine (T4MPD) has been investigated by means of ESR spectroscopy. The observed spectra after uv irradiation of both isotactic-PP (IPP) and stereoblock-PP (SPP) samples in vacuum at 77 K consisted principally of a broad singlet which was assigned to a T4MPD cation radical (T4MPD+·). On the other hand, the spectrum observed after irradiation of an atactic polypropylene (APP) sample at 77 K in vacuum was resolved into several components which decayed almost up to ca. 263 K to give rise to the broad singlet of T4MPD+·. One component was a sharp quartet which was assigned to a methyl radical, ·CH3·. The other component, a singlet, was attributed to a trapped electron, et?.By comparison of the ESR spectrum of deuterated T4MPD with that of the normal compound it was found that 60 ~ 70% of the methyl radicals arose from the added T4MPD due to β-scission, which also formed the N,N,N′-trimethyl-p-phenylenediamine radical, T3MPD·. The T3MPD· radical presumably captures an electron at lower temperatures to become a carbanion, T3MPD?, which releases the electron to reproduce the T3MPD· radical at elevated temperatures. This production of the radical T3MPD· due to the liberation of an electron provides an explanation for the observed increase in intensity of the decay curve in the temperature range from ? 168 K to 185 K. The remaining fraction, 30 ~ 40%, of the total methyl radicals was produced from the PP matrix by an energy transfer from the excited T4MPD1 to the PP matrix. The broad singlet which appeared in the temperature range near 195 K was attributed to an acyl radical ~CH2CH(CH3)CH2?O from the observed g-value. By photoillumination of this sample this broad singlet was converted reversibly into the quartet which was assigned to the radical ~CH2CH(CH2·)CH2CHO. 相似文献
The ammonia chemical ionization desorption spectra of N,N-dimethyl quaternary ammonium iodides in addition to high protonated molecular ion [M + H]+ intensity, show signals for an ion radical composed of N-methyl abstracted salt cation and ammonia [C + NH3? CH3]+˙. These ions corresponding to the cation +2 show increased importance in the chemical ionization mode, using the same reagent gas. The technique of chemical ionization desorption appears suitable for the analysis of salts, and thus for the determination of the molecular weight of both anion and cation. 相似文献
The photopolymerization of vinyl monomers (methyl methacrylate and styrene) was investigated in the presence of chlorosilane compounds. It was found that these additives acted as photosensitizers. In the case of the photopolymerization of methyl methacrylate, the rate of polymerization was found to be proportional to the concentration of methyl methacrylate and to the square root of the chlorosilane concentration. The chain-transfer constants of these photosensitizers, SiCl4, CH3SiCl3, (CH3)2SiCl2, (CH3)3-SiCl, and (CH3)4Si, with ultraviolet irradiation were 25.6 × 10?3, 18.4 × 10?3, 17.5 × 10?3, 14.4 × 10?3 and 0.5 × 10?3, respectively, for methyl methacrylate. 相似文献
A novel metal‐free initiator, i.e. the salt of the tetrakis[tris(dimethylamino)phosphoranylidenamino]phosphonium (P5+) cation with the 1,1‐diphenylhexyl (DPH–) anion was prepared by cation metathesis. It initiates a very fast and controlled anionic polymerization of methyl methacrylate in THF. Kinetic investigations between –20 and +20°C using a flow tube reactor provide nearly linear first‐order time‐conversion plots with half‐lives below 0.1 s, a linear dependence of the number‐average degree of polymerization, and rather narrow molecular weight distributions (Mw/Mn ≈ 1.2). 13C NMR measurements on a model of the active chain end (the P5+ salt of ethyl isobutyrate) in THF‐d8 show 15 and 25 ppm upfield shifts of the α‐carbon compared to the dimers and tetramers of the lithium ester enolate, respectively, indicating a non‐aggregated structure and an increased charge density on the α‐carbon. 相似文献
Abstract Laser flash photolysis and pulse radiolysis have led to the characterisation of several shortlived intermediates formed after irradiation of retinoic acid and retinyl acetate in hexane or methanol. For retinoic acid, the triplet state, wavelength maximum 440 nm, extinction coefficient 7.3 × 104 dm3 mol?1 cm?1, decay constant 6.2 × 105 s?1, is formed with a quantum yield of 0.012 for 347 nm excitation. The radical cation, absorption maximum 590 nm, extinction coefficient ~7 × 104 dm3mol?1 cm?1, is formed in a biphotonic process. The radical anion, absorption maximum 510nm in hexane, 480 nm in methanol where its extinction coefficient is 1.2 × 105 dm3mol?1 cm?1, appears to decay partially in methanol into another longer-lived neutral radical, wavelength maximum 420 nm, by loss of OH?. For retinyl acetate, the triplet state, absorption maximum 395 nm, extinction coefficient 7.9 × 104dm3mol?1 cm?1, decay constant 1.2 × 106s?1 is formed with a quantum yield of 0.025 for 347 nm excitation. Monophotonic photoelimination of OCOCH3? in methanol produces the retinylic carbenium ion, wavelength maximum 590 nm, whose decay is enhanced by ammonia, k ~ 2 × 106 dm3 mol?1 s?1 and retarded by water. The radical cation also has a wavelength maximum at 590 nm, its extinction coefficient being ~ 1.0 × 105 dm3mol1 cm?1. The long-lived transient absorption with maximum at 385 nm, extinction coefficient 1.0 × 105 dm3mol?1 cm?1, obtained from the reaction of the solvated electron with retinyl acetate in methanol may be due to either the radical anion itself or more likely the radical resulting from elimination of OCOCH3? from this anion. These results suggest that skin photosensitivity caused by retinyl acetate might be greater than that due to retinoic acid. 相似文献
The cationic bridged zirconocene complex [iPr(Cp)(Ind)Zr(Me)(THF)][BPh4] ( 1 ‐BPh4) was synthesized. Polymerization of methyl methacrylate with 1 ‐BPh4 in CH2Cl2 at temperatures between –20 and 20°C led to the formation of isotactic poly(methyl methacrylate). The low polydispersity index of the polymer obtained and a successful two step polymerization of methyl methacrylate with 1 ‐BPh4 are hints towards a living polymerization mechanism. 1H and 13C NMR analysis revealed an enantiomorphic site‐controlled mechanism for the formation of isotactic poly(methyl methacrylate). 相似文献
Three ternary luminescent complexes, Eu (deuterated 1,3-diphenyl-1,3-propanedione)3(1,10-phenanthroline), Eu (deuterated 1,3-diphenyl-1,3-propanedione)3(2,2′-bipyridine), and Eu (deuterated 1,3-diphenyl-1,3-propanedione)3 (bathophenanthroline) were synthesized using bidental oxygen and nitrogen as ligands. Luminescent polymers were fabricated by incorporating deuterated Eu(III) complexes in a poly(methyl methacrylate) matrix. Luminescent poly(methyl methacrylate) containing Eu (deuterated 1,3-diphenyl-1,3-propanedione)3 (bathophenanthroline) exhibited relatively higher quantum yield, faster radiation rate, sharper red emission and larger stimulated emission cross-section (quantum yield 36%, radiation rate 8.6 × 102 s?1, full width at half maximum 3.4 nm, and stimulated emission cross-section σp = 1.4 × 10?20 cm2) of the PMMA matrix. The value of σp was the same order as the values of Nd-glass laser for practical use. Additionally, the thermal behaviors of the Eu(III) ternary complexes were studied, and the results indicated that all of them can be long-term used in high temperature environment. Prepared luminescent polymer including Eu (deuterated 1,3-diphenyl-1,3-propanedione)3 (bathophenanthroline) showed promising results for applications in novel organic Eu(III) devices, such as high-power laser materials and optical fibers. 相似文献
It was found that free radicals of poly(methyl methacrylate) (PMMA) were formed by addition of the spin trapping agent, 2,6,-di-chloro-nitrosobenzene (DCNB), to a PMMA-benzene solution. This PMMA radical was detected by the spin adduct with DCNB. It was identified as a chain scission radical by the analysis of the ESR spectrum and experiments using samples of PMMA deuterated either in the α-methyl or in the ester methyl group. Since DCNB is known to abstract hydrogen from other molecules, the main chain scission of PMMA caused by the action of DCNB is an indirect process resulting from a ß-scission of the PMMA radical after a methylene hydrogen has been abstracted. 相似文献
A 4 K matrix ESR study shows that the molecular radical cations of isopropyl formate and acetate, produced radiolytically in halocarbon matrices at 4.2 K, undergo spontaneous rearrangement due to a selective intramolecular hydrogen shift from the tertiary CH bond in the isopropyl group to the carbonyl oxygen atom giving RC+(OH)OC(CH3)2, where R = H or CH3. The radical cation of tert-butyl acetate undergoes further fragmentation at the ester CO bond following a similar rearrangement to give an isobutene radical cation in CFCl3. 相似文献
S-Methyl thiomethacrylate (methyl thiolmethacrylate, MTMA) was polymerized with a variety of anionic initiators such as n-BuLi, octylpotassium, PhMgBr, and Et2AlNPh2 in toluene and THF. Stereoregularity of the polymer (PMTMA) was determined from the 1H-NMR spectrum of poly(methyl methacrylate), which had been derived from PMTMA, because the α-methyl resonance in the 1H-NMR spectrum of PMTMA was not satisfactorily solved owing to the overlap of pentad signals. The 13C-NMR spectrum of PMTMA also showed the splitting due to pentad sequences. Stereoregularity of PMTMA was always low compared with that of poly(methyl methacrylate), which was prepared under the same reaction conditions. MTMA was much more reactive than methyl methacrylate and methacrylonitrile in the copolymerization with n-BuLi in toluene and in THF at ?78°C. The lower stereoregulation of the polymerization of MTMA and the higher reactivity of MTMA were mainly ascribed to the higher resonance effect of MTMA. 相似文献
The salts 3‐[(2,2,3,3‐tetrafluoropropoxy)methyl]pyridinium saccharinate, C9H10F4NO+·C7H4NO3S−, (1), and 3‐[(2,2,3,3,3‐pentafluoropropoxy)methyl]pyridinium saccharinate, C9H9F5NO+·C7H4NO3S−, (2), i.e. saccharinate (or 1,1‐dioxo‐1λ6,2‐benzothiazol‐3‐olate) salts of pyridinium with –CH2OCH2CF2CF2H and –CH2OCH2CF2CF3meta substituents, respectively, were investigated crystallographically in order to compare their fluorine‐related weak interactions in the solid state. Both salts demonstrate a stable synthon formed by the pyridinium cation and the saccharinate anion, in which a seven‐membered ring reveals a double hydrogen‐bonding pattern. The twist between the pyridinium plane and the saccharinate plane in (2) is 21.26 (8)° and that in (1) is 8.03 (6)°. Both salts also show stacks of alternating cation–anion π‐interactions. The layer distances, calculated from the centroid of the saccharinate plane to the neighbouring pyridinium planes, above and below, are 3.406 (2) and 3.517 (2) Å in (1), and 3.409 (3) and 3.458 (3) Å in (2). 相似文献
The temperature dependence of the ESR spectra of poly(methacrylic acid) and poly-(methyl methacrylate) γ-irradiated at room temperature was studied between ?196°C and +25°C. The conventional 9-line spectrum was observed throughout this range with no significant spectral change, in contrast to the propagating radical ··· CH2? °C(CH3)COOR found in methacrylic acid monomer or barium methacrylate dihydrate irradiated at ?196°C. In addition, the irradiation of methacrylic acid monomer with a low dose at 0°C gave the same 13-line spectrum as that of the propagating radical obtained by the irradiation at ?196°C, while prolonged irradiation at 0°C gave the same conventional 9-line spectrum as that of poly(methacrylic acid) or poly(methyl methacrylate). The conventional 9-line spectrum has a much weaker 4-line component than that of the propagating radical. The difference comes from the surrounding matrix, and the conventional 9-line spectrum is well interpreted by introducing the concept of the distribution of the conformational angle in the irregular polymer matrix. From simulation of the ESR spectrum, it was found that the intensity of the 4-line component is very sensitive to the distribution, and that the observed 9-line spectrum is well reproduced assuming a Gaussian distribution (half-height width of 5–6°) around the most probable conformation which is nearly the same as that of the propagating radical, where the conformational angles of the two C? Hβ bonds to the half-filled p-orbital are 55° and 65°. 相似文献