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1.
Determination of tacticity of polypropylene sulphide is studied by NMR. The measurements made by 13C-NMR are compared with those obtained by 1H 100 MHz NMR on corresponding selectively deuterated polymers. The good correlation between the two sets of results shows that stereoregularity of polypropylene sulphide can be easily found with 5 per cent precision. 相似文献
2.
Ethylene sulphide-isobutylene sulphide and propylene sulphide-isobutylene sulphide copolymers have been prepared using anionic catalysts and investigated by 13C-{1H} NMR spectroscopy. The carbon-13 NMR spectra are assigned in terms of diad and triad sequences. There is discussion of the effects of mono- or dimethyl substitution in the α, β, γ or δ positions on the chemical shift of the main chain carbon atoms. It has also been shown that for isobutylene sulphide, as for propylene sulphide, under the influence of an anionic catalyst, there is a normal ring opening only at the primary carbon atom. 相似文献
3.
C. M. Paleos G. P. Evagelatos Photis Dais G. Kipouros 《Journal of polymer science. Part A, Polymer chemistry》1979,17(6):1611-1618
In the present study the polymerization of 4-vinyl-N-methylpyridinium methylsulfate at liquid–liquid interfaces is investigated. Various experimental procedures that may favor the interfacial mode of polymerization over the isotropic one are discussed. The effectiveness of the methods was evaluated by physical characterization studies and particularly polymer tacticity. This last property is directly associated with the achieved organization of the monomers at interfaces. 13C-NMR technique was used for tacticity determination. According to tacticity, random polymers are primarily obtained that result from an isotropic polymerization in the aqueous phase, where the monomer is extremely soluble. The small predominance of the syndiotactic triad over the isotactic one is explained by the occurrence of an interfacial polymerization induced by the orientation of the monomers. A polymerization model is proposed that justifies the stereospecificity modification of polymerization. 相似文献
4.
M. G. Pérez-García M. Rabelero S. M. Nuño-Donlucas E. Mendizábal A. Martínez-Richa R. G. López 《高分子科学杂志,A辑:纯化学与应用化学》2013,50(7):539-546
The effect of monomer feeding rate on particle size, molar masses, glass transition and tacticity of poly(n-butyl methacrylate) (PBMA) nanoparticles synthesized by semi-continuous heterophase polymerization under monomer-starved conditions is reported. Three feed rates were examined. Highly monomer-starved conditions at the two slower addition rates were confirmed by the low amount of residual monomer throughout the reaction and by the fact that the instantaneous polymerization and feeding rates became similar at later stages of the reaction. Under these conditions, polymer particles in the nanometer range (30 to 35 nm) were obtained. Glass transition temperatures are substantially higher than those reported for commercial PBMA. Polymers tacticity was determined by 13C-NMR spectroscopy. NMR measurements confirm that the syndiotactic content of the PBMA synthesized here is larger than those of the commercial ones made by free-radical polymerization. Molar masses are much lower than those expected from termination by chain transfer to monomer, which is the typical termination mechanism in microemulsion polymerization. 相似文献
5.
Jean Pierre Quaegebeur Tadao Seguchi Henri Le Bail Claude Chachaty 《Journal of polymer science. Part A, Polymer chemistry》1976,14(11):2703-2724
The γ-ray-induced postpolymerization of acrylonitrile and methyl methacrylate adsorbed on Linde zeolite 13X irradiated at 77°K has been studied between 303 and 343°K as a function of the amount of adsorbed monomer and of the irradiation dose. The change in the nature and the concentration of free radical with temperature and duration of the postpolymerization was followed by the ESR method, whereas the formation of polymer was monitored continuously by the decay of the 1H-NMR absorption line of the monomer under high-resolution conditions. It was found that the overall postpolymerization kinetics may be accounted for by assuming an exponential decay of radical propagation and recombination reactions with chain length. The tacticity of the polymer recovered by destroying the matrix in hydrofluoric acid was determined by 13C-NMR. The probability of isotactic addition of AN and MMA is larger than in the radical polymerization in solution owing likely to the association of adsorbed monomer molecules in pairs preforming an isotactic diad. 相似文献
6.
7.
The methoxy 1H-NMR assignments in the 2.1–3.7δ region for styrene/methyl methacrylate copolymers have been assessed in terms of pentad sensitivity. Several of the methoxy resonances suggested by this study differ from literature assignments. The evidence in support of these reasignments is based on a comparison of calculated and observed triad distributions and on the good agreement of the value of the reactivity ratio rM calculated from individual triads with that obtained by classical methods. A new procedure for the determination of the tacticity coefficient σ is applied. 相似文献
8.
Donald J. A. Cameron Michael P. Shaver 《Journal of polymer science. Part A, Polymer chemistry》2012,50(8):1477-1484
The synthesis of a family of polymer stars with arms of varied tacticities is discussed. The effect of polymer tacticity on the physical properties of these polymer stars is dramatic. Dipentaerythritol cores support six poly(lactic acid) arms. Lewis acidic tin and/or aluminum catalysts control the polymerization to afford polymer stars of variable tacticity. Analysis of these polymers by 1H NMR spectroscopy, thermogravimetric analysis, powder X‐ray diffraction, and differential scanning calorimetry reveals the effects of tacticity control on the physical properties of the polymer stars. Hydrolytic decomposition studies suggest that the degradation profile of a polymer star may also be tuned by stereochemical control. Differences between isotactic samples derived from rac‐lactide and L ‐lactide are heightened by longer arms of 50 and 100 monomer units. Control of polymer isospecificity shows that a ~70% isotacticity bias is necessary to induce crystallinity and alter the thermal and degradation properties of the material. Above 70% isotacticity, the degradation properties and thermal transitions can be further tuned across a relatively wide range. This technique allows for significant tunability to the physical properties of aliphatic polyester polymer stars. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012 相似文献
9.
T. Higashimura Y. Ohsumi K. Kuroda S. Okamura 《Journal of polymer science. Part A, Polymer chemistry》1967,5(4):863-875
Highly crystalline poly(methyl vinyl ether) (PMVE) was produced in toluene in a temperature range of 0 to ?20°C. with the use of sulfuric acid–aluminum sulfate complex (SA catalyst). It was found from the NMR spectra that these polymers contained more than 50% of the triad isotactic fraction and the melting point of the unfractionated polymer was about 130°C. However, PMVE containing a large amount of the isotactic fraction was insoluble in nitromethane, so the triad tacticity of highly crystalline PMVE could not be quantitatively determined. The molecular weight of PMVE increased with increasing conversion and increasing polymerization temperature. This behavior is different from that in metal halide catalysts. Also, the stereoregularity of PMVE decreased with increasing monomer concentration. However, addition of a polar solvent and increasing the polymerization temperature had little effect on the stereoregularity of the polymer. The increase in the isotactic fraction at high catalyst concentration and the difference in the monomer composition in the copolymerization of methyl vinyl ether with 2-chloroethyl vinyl ether by SA catalyst from that obtained by BF3·O(C2H5)2 suggest that the absorption of MVE on a catalyst surface is an important step in the propagation step by SA catalyst. The fraction of the triad tacticity calculated from the enantiomorphic catalyst sites model8 coincided with the experimental results. This fact shows that the steric structure of the adding monomer is determined only by the nature of the catalyst irrespective of the nature of a growing chain end. It is concluded, on considering also the results of the previous paper, that completely different factors can control the steric structure of a polymer even for the same monomer when different catalysts are used. 相似文献
10.
The 13C-(1H) NMR spectra of poly(vinyl chloride sulfone)s with macroscopic compositions corresponding to the ratio vinyl chloride (V):SO2(S) = n from ca. 1 to 4 have been analyzed in terms of comonomer sequences and configurational placements. In the copolymer with n ? 1, methylene and methine carbons in SVS sequences were resolved and were sensitive to “across SO2” tacticity. No SVS sequences were observed in the copolymer with n = 2.0, confirming that it had a regular SVVS structure, which also showed a high “internal” stereosequence regularity. It was not possible to discriminate the methylene or methine carbon atoms in S(V)n S sequences with n ≥ 2. 相似文献
11.
Ronald Shelden Takayuki Fueno Junji Furukawa 《Journal of Polymer Science.Polymer Physics》1969,7(5):763-773
Triad tacticity data obtained by NMR analysis have previously been interpreted in terms of two basic statistical models in order to elucidate the stereospecific polymerization mechanism. In this paper the characteristics of these two basic models for stereospecific polymerization, the enantiomorphic-sites (EMS) model, and the polymer-end control (PEC) model, are examined and compared. The tacticity values accessible to the two-parameter EMS model, which includes the influence of the chain end unit, are shown to be highly restricted. Only about 20% of the isotacticity versus syndiotacticity plot is accessible to this model. To this extent the consistency of a set of triad tacticity data with the model can be tested. No such tacticity limits are exhibited by the two-parameter PEC model, which includes the influence of the penultimate unit. Any set of tacticity values which can be interpreted in terms of the two-parameter EMS model can also be interpreted in terms of the two-parameter PEC model. 相似文献
12.
Radical poly(naphthyl-1 methacrylate) and poly(naphthyl-2 methacrylate) have been examined by [13C]NMR. Quantitative determination of the tacticity of pentads is only possible with poly(naphthyl-2 methacrylate). The propagation of the stereosequences is found to be nearly bernouillian. 相似文献
13.
Difficulties in the precipitation of Group II of the classical scheme of qualitative inorganic analysis are discussed. Three reagents for the destruction of permanganate and dichromate have been examined; hydrogen peroxide was found to be most suitable. Conditions have been established whereby As2S5 can be precipitated, thus avoiding the necessity for reducing AsV before passing hydrogen sulphide. A simple separation of the Group IIB elements, based on the stepwise precipitation of their sulphides from solutions of controlled acidity, is proposed.These modifications have been adapted to the procedures of Holness2 and Holness and Trewick1, for adjusting the acidity and for dividing the sulphide precipitates into the two sub-groups. 相似文献
14.
D, L-Cis-2-aminocyclobutane-1-carboxylic acid NCA, D, L-cis-and trans-2-aminocyclohexane-1-carboxylic acid N-carboxyanhydride (NCA) and D, L-cis-2-aminocyclohexane-1-carboxylic acid NCA were polymerized under various conditions. The 13C-NMR spectra of the resulting β-polyamides measured in trifluoro-acetic acid show splittings of all signals reflecting diads and triads. Poly-D, L-3-aminobutyric acid obtained by anionic polymerization of D, L-4-methyl acetidinone does not display tacticity effects in its 13C-NMR spectrum. Hence it is concluded that tacticity effects are observable only if both α- and β-carbons have a substituent. Furthermore, it was found that the reaction conditions do not have a strong influence on the stereospecificity of the NCA-polymerization. In all cases nearly random sequences of D and L-units were obtained. 相似文献
15.
Interactions between poly(vinylpyrrolidone) (PVP) and p-hydroxyben-zoic acid-formaldehyde copolymer have been studied in methanol solution. The component polymers appear to form interpolymer complexes in distinct stages. The results are interpreted in terms of 1) hydrogen bonding, 2) ion-dipole interaction, 3) tacticity of PVP, and 4) multiple coordinating positions of component polymers. 相似文献
16.
Elizabeth F. Mccord Waifong L. Anton Lech Wilczek Steven D. Ittel Lissa T. J. Nelson Keith D. Raffell Joan E. Hansen Charles Berge 《Macromolecular Symposia》1994,86(1):47-64
1H NMR and 13C NMR have been used to study the end groups and tacticity in PMMA macromonomers and oligomers. These macromonomers are terminated almost exclusively in one vinylidene group per chain. The end group signals from the macromonomers are identified in both the 13C and 1H NMR spectra. The spectra of the purified oligomers (n = 1-4) were used to aid in assignment. The macromonomers are predominantly syndiotactic, and the tacticity measured is consistent with Bernoullian statistics. The tetramer is a mixture of r and m isomers in a 4:1 ratio. It is shown that T1 experiments can provide a useful method of distinguishing resonances due to low molecular weight impurities from those due to stereochemical or isomeric effects in macromonomers. The absence of internal double bonds was confirmed by isomerizing the vinylidene group of several oligomers and of the macromonomer, and verifying the absence of the isomerized signals in the NMR spectra of the original materials. 相似文献
17.
A monitor, based on a sulphide ion-selective electrode, has been developed and applied to measure the total dissolved sulphide concentration (0.01–100 mg kg-1) in heavy water plant effluents. The monitor is reliable and accurate, and has minimal maintenance and calibration requirements under continuous operation. The Orion 94-16A sulphide electrode gives Nernstian response to sulphide concentrations as low as ca. 0.01 mg kg-1 in strongly alkaline solutions in the presence of anti-oxidants, but its sensitivity decreases with use. One electrode failed to give Nernstian response to sulphide concentrations below 1 mg kg-1. 相似文献
18.
E. L. Madruga J. San Romn J. Alcalde M. C. Fernandez-Monreal 《Journal of polymer science. Part A, Polymer chemistry》1988,26(8):2281-2290
Methyl α-p-cyanobenzylacrylate was synthesized from dimethyl malonate following well-known organic reactions. The purified monomer was polymerized by a free-radical mechanism in benzene solution, using AIBN as initiator in the interval 50–90°C. The kinetic results seem to indicate an apparent ceiling temperature near 90°C. The analysis by 13C-NMR of polymers obtained indicates that the macromolecular chains are predominantly syndiotactic and the tacticity is independent of the polymerization temperature in the experimental interval studied. However, the determination of conditional probabilities for iso- and syndiotactic additions and the persistence ratios indicate that the propagation mechanism for the radical polymerization of methyl α-p-cyanobenzylacrylate does not follow a typical Bernoullian statistics. 相似文献
19.
I.B. Rashkov G. Merle Q.T. Pham V.C. Shishkova J.P. Pascault I.M. Panayotov 《European Polymer Journal》1982,18(1):37-41
The bulk polymerization at -24° of α-methylstyrene initiated by the alkali metals and the graphitides LiC12, KC24 and KC36 has been studied. The tacticities of polymers have been measured by [1H] NMR. The alkali metals give polymers having the same tacticity and the propagation of the stereoconfiguration is bernouillian; LiC12 yields more racemic diads while KC24 and KC36 yield more meso diads and show a penultimate effect. By measuring the growing of the thickness of KC24 flakes, it appears that the more sterically hindered a monomer the more slowly it penetrates into the graphitide. The copolymerizations at 25° of styrene with 1-1 diphenylethylene or 1–2 diphenylethylene (trans stilbene) (comonomer ratio 1/1) initiated by KC24 in tetrahydrofuran (THF), xylene (XL), decahydronaphthalene (decalin DL) and cyclohexane (CH) have been studied. The amount of styrene units in the copolymers depends on the nature of the solvent: it increases as the interaction solvent-graphitide decreases. All the results support the view that the polymerization proceeds between the graphite layers. 相似文献
20.
The mixed ligand complex formation had been studied in the aluminate-fluoride, gallate-fluoride, aluminate-sulphide and gallate-sulphide systems by spectrophotometric as well as potentiometric methods using glass and sulphide selective electrodes. The formation of the species Al(OH)3F? and Ga(OH)2S? has been demonstrated and the equilibrium constants have been determined. Similar interaction could not be detected in the aluminate-sulphide and gallate-fluoride systems.The differences in behaviour of the metal ions to the characteristically hard fluoride and soft sulphide ligands can be interpreted in that the Ga3+ ion may form complexes with charged soft ligands too, its behaviour then differing from that of the typically hard Al3+ ion. 相似文献