Stereoregiilarity of Polyacrylonitrile by High Resolution 13C NMR Analysis
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Polyacrylonitrile
Tacticity
Triad (sociology)
Carbon fibers
Tacticity
Triad (sociology)
Isopropyl
Polypropylene
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Polyacrylonitrile
Tacticity
Triad (sociology)
Carbon fibers
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Abstract 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.
Tacticity
Triad (sociology)
Stereospecificity
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Sequence (biology)
1-Butene
Butene
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Tacticity
Ziegler–Natta catalyst
Polypropylene
Post-metallocene catalyst
Active center
Coordination polymerization
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Abstract It is shown that, by assuming that each of the peaks resolved in the CCl stretching region of the Raman spectra of a series of poly(vinyl chloride) gels can be associated with a definite triad structure, most of the peaks can he assigned to syndiotactic, isotactic, or heterotactic triad configurations without reference to the spectra of model compounds or to vibrational calculations. The results are in general agreement with most previous assignments except for the assignment of the peak at 646 cm –1 . Previously this was assigned to syndiotactic material, but it is here assigned to a structure consisting of consecutive syndiotactic, isotactic, and syndiotactic placements in a conformation not very distorted from the planar zigzag conformation.
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Triad (sociology)
Zigzag
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Abstract The aqueous polymerization of methyl methacrylate was carried out in the absence and in presence of corundum or carborundum at 25 and 80°C. In the absence of corundum and carborundum, it has been found that rising the polymerization temperature from 25 to 80°C resulted in changing the tacticity of the obtained polymers. At 25°C the isotactic triad was 26% while the heterotactic triad was 33.5% and the syndiotactic one was 40.5%. Increasing the polymerization temperature to 80°C resulted in a decrease of the isotactic structure to 0% and increased the heterotactic structure and syndiotactic structure to 48 and 52% respectively. Polymerizing at 25°C in presence of corundum (0.5 g) an increase in the syndiotactic triad took place from 40.5 to 50.7% while the isotactic triad decreased from 26 to 22.2% and the heterotactic structure decreased from 33.5 to 27%. Raising the polymerization temperature to 80°C in the presence of the same amount of corundum resulted in an increase in both the isotactic and heterotactic triads to 35 and 32.7%, respectively. Polymerizing at 80°C in presence of corundum (0.5 g) resulted in nearly an equal percentage of each triad 33%.
Tacticity
Triad (sociology)
Corundum
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Tacticity
Polypropylene
Proton NMR
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Tacticity
Polymethyl methacrylate
Proton NMR
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Abstract The NMR spectrum of polyacrylonitrile is interpreted and the tacticity of three polyacrylonitrile samples prepared at different temperatures in the range from −78 to 120°C. determined. The ratio between isotactic and syndiotactic units is about 50:50 for all the three samples examined.
Polyacrylonitrile
Tacticity
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