Using 26 NMR spectrometers, the Research Group on NMR, the Society of Polymer Science, Japan observed the 1H NMR chemical shift, resolution, and signal intensity; 13C NMR chemical shift, resolution, and signal intensity; the effect from initiator fragment signal; 1H spin-lattice relaxation times; 13C spin-lattice relaxation times; and 13C nuclear Overhauser enhancement of radically polymerized poly(methyl methacrylate). Excellent reliability was found after comparison between the data from different spectrometers. Molecular motion of this polymer was analyzed with a term of 3τ model. 相似文献
The vacuum photodegradation at 30°C. of poly(methyl methacrylate) and copolymers with acrylaldehyde, methacrylaldehyde, and methyl acrylate has been studied. The polymers were examined in the form of expanded films as produced by a freeze-drying technique. At least one molecule of carbon monoxide is evolved for each chain scission. It is concluded that chain scission in poly(methyl methacrylate) is primarily the result of photoinduced aldehyde groups. 相似文献
Anthracene-labelled poly(methyl methacrylate) (PMMA) was prepared via atom transfer radical polymerization (ATRP) where 9,10-bis(chloromethyl)anthracene and CuCl/2,2′-bipyridine were used as the initiator and catalyst, respectively. Both the linear increase of the number average molecular mass with conversion and the narrow polydispersity in the resulting polymers suggest that the polymerization proceeds in a “living” fashion and the anthracene molecule is incorporated into the middle of the polymer backbone. The initiation efficiency was low, ca. 13%, presumably due to some side reactions which compete with the initiation reaction. 相似文献
Methanol-induced opacity in poly (methyl methacrylate) (PMMA) is investigated subject to two cooling processes; furnace cooling and air cooling. The glass transition temperature of PMMA decreases with increasing time of exposure to methanol at 40–60°C and then increases during cooling, due to progressive desorption. Voids form during cooling as long as specimen temperature remains above its glass transition temperature. Since furnace cooling affords enough time for holes to expand larger than the light wavelengths, the transmittance of furnace-cooled PMMA is independent of wavelength. The transmittance of PMMA subjected to rapid cooling in the air is wavelength dependent due to scattering by holes smaller than light wavelengths. The transmittance of PMMA bearing a given weight gain of methanol (measured at absorption temperature) prior to cooling for furance cooling is lower than that for the same material subjected to air cooling. A sharp front between outer and inner regions is found in specimens removed quickly from the thermostated water bath to air at ambient temperature. 相似文献
Mercapto-16-crown-5 was prepared starting from tetraethyleneglycol and 3-chloro-2-chloromethyl-1-propene. Radical polymerization of methyl methacrylate was carried out in the presence of mercapto-16-crown-5 as a chain transfer agent to give crown ether-terminated poly(methyl methacrylate). The end crown group was characterized by IR and 1H-NMR spectra. Sodium cation was selectively extracted by this crown-containing polymer. The molecular weight of the obtained polymer had influence upon the ability of extraction of sodium cation. 相似文献
In poly(methyl methacrylate) films, the kinetics of the oxidation of polymeric radicals and azobenzenenitrenes with molecular oxygen dissolved in the polymer is studied. The free radicals are produced at 77 K by irradiating the polymer with UV light, fast electrons, or γ rays. The concentration of oxygen is varied from 4.5 × 1018 to 3.1 × 1019 cm?3; the temperature of the reaction, from 90 to 130 K. The reaction is carried out in excess oxygen. The kinetics of radical oxidation is shown to be independent of the type of radiation that stimulates the formation of radicals and coincides with the kinetics of the oxidation of azobenzenenitrenes, which are uniformly dissolved in the polymer. It is concluded that the structure of the polymer in the vicinity of the radicals is virtually the same as the structure of the polymer bulk. The activation energy of the oxygen diffusion coefficient calculated according to the radical oxidation kinetics amounts to ~30 kJ/mol. 相似文献
As an important phthalate plasticizer, dibutyl phthalate (DBP) was employed to decrease the bonding temperature of poly(methyl methacrylate) (PMMA) microfluidic chips in this work based on the fact that it can lower the glass transition temperature of PMMA. The channel plates of the PMMA microchips were fabricated by the UV-initiated polymerization of prepolymerized methyl methacrylate between a silicon template and a PMMA plate. Prior to bonding, DBP solution in isopropanol was coated on PMMA covers. When isopropanol in the coating was allowed to evaporate in air, DBP was left on the PMMA covers. Subsequently, the DBP-coated covers were bonded to the PMMA channel plates at 90 °C for 10 min under pressure. The channels in the complete microchips had been examined by optical microscope and scanning electron microscope. The results indicated that high quality bonding was achieved below the glass transition temperature of PMMA (∼105 °C). The performance of the PMMA microfluidic chips sealed by plasticizer-assisted bonding has been demonstrated by separating and detecting ionic species by capillary electrophoresis in connection with contactless conductivity detection. 相似文献
Thermoluminescence of poly(methyl methacrylate) (PMMA) irradiated with x rays, has been studied in the temperature range 100 to 460°K. Two glow peaks with maxima at 136 and 368°K have been observed. These are analyzed by three methods and the results are compared. Both curves obey second order kinetics and correspond to activation energies of 0.17 and 0.88 eV, respectively. It is possible to identify the centers responsible for the two peaks by correlation with electron spin resonance and optical data obtained for the same samples irradiated under the same conditions. Spectral studies of the emission show that the low temperature peak has its maximum at 365 nm while the high temperature peak has its maximum at 480 nm. 相似文献
Anionic polymerization of methyl methacrylate (MMA) was carried out in tetrahydrofuran (THF) or THF/toluene mixture at ?78°C initiated by triphenylmethyl sodium or lithium as initiators. Highly syndiotactic PMMA of low polydispersity (Mw/mn = 1.11–1.17) could be prepared with triphenylmethyl lithium in THF or THF/toluene mixture at ? 78°C. Moreover, PMMA macromonomer having one vinylbenzyl group per polymer chain was prepared by the couplings of living PMMA initiated by triphenylmethyl lithium with p-chloromethyl styrene (CMS) at ?78°C. The coupling reaction of living PMMA initiated by triphenylmethyl sodium with CMS was scarcely occurred. 相似文献
A viscometric determination of the degree of branching γ, of poly(methyl methacrylate) obtained by anionic polymerization proved the reaction of the growing center of poly(methyl methacrylate) with the ester group of another polymer molecule, accompanied by the formation of a trifunctional branch point. This reaction occurs if the solution polymerization of methyl methacrylate is initiated: (1) with butyllithium at ?78°C only on attaining 100% conversion and after a long time or at +20°C immediately after the polymerization has set in; (2) with lithium tert-butoxide at +20°C after a long time. The degree of branching of poly(methyl methacrylates) obtained under similar conditions in the presence of tetrahydrofuran reaches higher values than for polymers prepared in toluene. The tacticity of polymers does not affect the experimentally determined γ values. 相似文献
Methyl methacrylate (MMA) was polymerized by radical initiation at 25°C in DMF in the presence of preformed isotactic PMMA (iMA) with about 90% isotactic triads and different M?v's, viz., iMA-1: 7.2 × 105; iMA-2, 5.0 × 105; iMA-3, 3.5 × 105; iMA-4, 1.25 × 105; and iMA-5, 1.15 × 105. The MMA:iMA ratio was 6:1. The collected polymers were separated into two fractions by extraction with boiling acetone and characterized by 60 MHz NMR. It is found that the M?v of the polymer formed ran parallel to the M?v of iMA. In all cases syndiotactic PMMA (s-PMMA) was produced which associated with the isotactic substrate to form acetone-insoluble stereocomplexes. The syndiotactic polymers probably consist of long syndiotactic and heterotactic sequences. The syndiotacticity decreased with conversion and was generally highest in the presence of iMA-1. With iMA-1 even the formation of some additional i-PMMA (in the acetone-insolubles) was indicated, especially in the later stages of the polymerization. Characterization of the acetone-soluble fractions indicated that i,s-stereoblock polymers were also produced, of which the persistence ratios ρ increased with the M?v of iMA. From these results it is concluded that this reaction differs from the conventional radical polymerization and can be considered a stereospecific replica polymerization, the driving force being the strong tendency of i- and s-PMMA to associate. The formation of i,s-stereoblock polymers and additional i-PMMA indicates that s-PMMA in its turn can also act as a polymer matrix. 相似文献
The kinetics of the bulk radical polymerization of methyl methacrylate and the structure and properties (physicomechanical and thermomechanical, as well as diffusion and sorption) of the polymers were examined in relation to the amount of low-molecular-weight poly(methyl methacrylate) added. 相似文献
Deuterium NMR and modulated differential scanning calorimetry (MDSC) were used to probe the behavior of ultrathin adsorbed poly(methyl acrylate) (PMA). The spectra for the bulk methyl-labeled PMA-d3 were consistent with the motions of the polymer segments being spatially homogeneous. For the polymers adsorbed on silica, multicomponent line shapes were observed. The segmental mobility of the surface polymers increased with increased adsorbed amounts. In contrast to the behavior of the polymers in bulk, the adsorbed lower-molecular-mass PMA-d3 was less mobile than the adsorbed high-molecular-mass polymer. The presence of a polymer overlayer was sufficient to suppress the enhanced mobility of the more-mobile segments of the adsorbed (inner) polymer. MDSC studies on adsorbed poly(methyl methacrylate) showed that the glass-transition temperature of the thin polymer films increased and broadened compared to the behavior of the polymer in bulk. The presence of a motional gradient with the less-mobile segments near the solid-polymer interface and the more-mobile segments near the polymer-air interface was consistent with the experimental observations. 相似文献
The spin trap agent, 2,6-di-chloronitrosobenzene (DCNB), which is decomposed into a nitrogen monoxide and a chlorinated phenyl radical on slight warming, was known to act as a radical generator through hydrogen abstraction by the chlorinated phenyl radical from an adjacent molecule. An ESR spectrum was observed at room temperature from a poly(methyl methacrylate) (PMMA)-benzene solution after the addition of DCNB followed by a warming to ca 30°C. The radical concentration increased with time. The spectrum was assigned to the spin adducts of PMMA radicals generated and trapped by DCNB. Analyses of the spectra observed from normal PMMA and partially deuterated PMMA's indicated that the majority of the PMMA radicals were the chain-scission species and a minority were . It was concluded that the main-chain scissions in PMMA were caused by the radicals (D), which had been primarily produced by the chlorinated phenyl radicals. These ESR data are supported by the fact that a decrease in molecular weight of PMMA was observed after addition of DCNB, and further reinforced by the fact that a molecular weight estimated from the number of the scission radicals agreed fairly well with the measured molecular weight. Similar results were obtained when both tri-chlorinated nitrosobenzene and tetra-chlorinated nitrosobenzene were used instead of DCNB. 相似文献