13 C NMR spectra of isotactic and syndiotactic poly(ethyl α‐chloroacrylate)s and poly(isopropyl α‐chloroacrylate)s were measured in toluene‐ d 8 at 25 MHz. The spectra were analyzed for triad, tetrad and pentad t...
13 C NMR spectra of isotactic and syndiotactic poly(ethyl α‐chloroacrylate)s and poly(isopropyl α‐chloroacrylate)s were measured in toluene‐ d 8 at 25 MHz. The spectra were analyzed for triad, tetrad and pentad tacticities comparing the spectra with the results previously obtained by 1 H NMR spectroscopy. Tetrad tacticities of the polymers were measured from the resonance of the backbone methylene carbon and favorably compared with tetrad values obtained by 1 H NMR. The resonance of the carbonyl carbon showed the peaks corresponding to the tactic triad with a pentad splitting in mm resonance. The triad values obtained from the carbonyl carbon resonance were in good agreement with those calculated from the tetrad values as well as the triad tacticities obtained by 1 H NMR. The quaternary carbon reconances were very complicated because the chemical shift differences for the different tactic triads were of the comparable magnitude with those for the pentads, and a tentative peak assignment was made with the aid of the statistical calculation of pentad values assuming first‐order Markovian statistics for the isotactic polymer and Bernoullian statistics for the syndiotactic polymer.
A review of recent work by the authors on a relaxation (Tgℓℓ) above the glass transition Tgof amorphous polystyrene is presented. On the basis of experimental data from torsional braid analysis (TBA), differential sca...
A review of recent work by the authors on a relaxation (Tgℓℓ) above the glass transition Tgof amorphous polystyrene is presented. On the basis of experimental data from torsional braid analysis (TBA), differential scanning calorimetry (DSC), and differential thermal analysis (DTA), and of an examination of the literature, it is suggested that Tℓℓrepresents a molecularly-based transition. Its main features are summarized by the expressions: Tℓℓ≃ 1.2 Tgand Tℓℓ≃Tℓℓ(∞)—KℓℓMn−1, where temperatures are in degrees Kelvin and Kℓℓis a constant. Jt follows that if Tgis an isofree-volume state, then so is TℓℓFurther, when Mn≃Mwand M for each component
Under identical conditions of cationic polymerization at low temperature 2‐( p ‐tolyl)‐1‐propene (α, p ‐dimethylstyrene) gave polymers with much higher syndiotactic contents than unsubstituted α‐methylstyrene....
Under identical conditions of cationic polymerization at low temperature 2‐( p ‐tolyl)‐1‐propene (α, p ‐dimethylstyrene) gave polymers with much higher syndiotactic contents than unsubstituted α‐methylstyrene. All samples of poly(α, p ‐dimethylstyrene) were crystalline, but poly(α‐methylstyrene) did not crystallize even at high degrees of stereoregularity. Similarly polymers of p ‐isopropyl‐α‐methylstyrene were crystalline, and the crystalline properties of copolymers of the three monomers were investigated and compared to those of the homopolymers. The rôles of stereoregularity and crystallizability in forming crystalline products were considered. Unter identischen Bedingungen der kationischen Polymerisation bei tiefer Temperature lieferte 2‐( p ‐Tolyl)‐1‐propen (α, p ‐Dimethylstyrol) Polymere mit höherem syndiotaktischem Gehalt als das unsubstituierte α‐Methylstyrol. Sämtliche Proben von Poly(α, p ‐dimethylstyrol) erwiesen sich als kristallin im Gegensatz zum Poly(α‐methylstyrol), das selbst bei hoher Stereoregularität nicht kristallisierte. Ähnlich erwiesen sich Polymere des p ‐Isopropyl‐α‐methylstyrols als kristallin. Die kristallinen Eigenschaften von Copolymeren der drei Monomere wurden untersucht und mit denen der Homopolymere verglichen. Die Rolle der Stereoregularität und der Kristallisierbarkeit bei der Bildung kristalliner Produkte wurde in Betracht gezogen.
The present status of work on the mechanism of the emulsion polymerisation of vinyl acetate initiated by potassium persulphate is critically reviewed. In addition, some new data illustrating the effect of adding elect...
The present status of work on the mechanism of the emulsion polymerisation of vinyl acetate initiated by potassium persulphate is critically reviewed. In addition, some new data illustrating the effect of adding electrolytes is presented. The polymerisation proceeds by a mechanism different from that of most vinyl monomers. In particular, the rates are approximately zero order on monomer from 20 to 85% conversion with only a minor dependence on the soap concentration and the number of particles. The dependence of the rate on the initiator concentration varies with different investigators from 0.5–1.0 order. The results are discussed in terms of various current theories and an attempt is made to rationalise them in a reasonable way.
The effects on adhesive joint strength of four pressure-temperature histories, each over the range of pressures from 1 to 1500 bars and temperatures from 25 to 200°C, has been investigated with polystyrene-Py...
The effects on adhesive joint strength of four pressure-temperature histories, each over the range of pressures from 1 to 1500 bars and temperatures from 25 to 200°C, has been investigated with polystyrene-Pyrex glass butt joint specimens. The various pressure-temperature histories were designed to show the separate effects of permanent stresses, transient stresses and interfacial contact on joint strength. This strength increased as the number of stress concentration loci were reduced through application of high contact pressures on the melt. However, isobaric solidification of the polymer led to a maximum in fracture stress as a function of applied molding pressure because of the existence of a critical pressure at which permanent thermal stresses were minimized. A series of isothermal compression-decompression molding operations showed fracture stress to increase with interfacial contact area until maximum contact was achieved. A 100 per cent gain in bond strength was realized when interfacial contact was maximized concurrent with minimizing both the permanent and transient stresses which normally develop when the adhesive joint is formed. Microscopic observations of interfaces in both non-fractured and fractured butt joints established a qualitative relationship between debonding, the mechanism of fracture, and joint strength.
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