Tacticity index

The only absolute method to measure the tacticity index (TI) of a polymer is nuclear magnetic resonance. All other methods give an Indirect measurement which depends on the tacticity of the polymer but also on other parameters, mainly the mean molecular veight of the polymer. This is illustrated in figure 6 and 7. 

Figure 10. NMR tacticity index as a function of polymerizotion temperoture bulk homopolymerization process - cocotalyst mDEAC...

By using the relation given in table 2, the stiffness nodulus at a reference MFI can be calculated. The aediua range NFI of 5 g/lOnin is chosen as a reference and the calculated value of the stiffness Modulus at this NFI is called GS. The dependence of this nomalized G Modulus auid of the NNR tacticity index on the polymerization tenperature can now be calculated. Both are linear as shown in table 3 and in figure 10 and 11. 

Table 3. NNR tacticity index and normalized stiffness modulus as a function of polymerization temperature - bulk homopolynerization process cocatalyst mOEAC - Units molar fraction for TI daN/cn for 65...

Figure 12. Relation between the reference G5 stiffness modulus and the NMR tacticity index - bulk homopolymerization process - cocatalyst mOEAC...

One of the consequences of the heterogeneity of Zeigler-Natta catalysts is that the active sites of such catalysts are not identical in terms of structure and reactivity. The polymer molecules formed by the different active sites are therefore not identical. They differ in molecular weights, microstructures, etc. Thus any measurement of molecular weight, branching, or tacticity index refers to a statistical average over many nonidentical polymer molecules. 

Solution times are sufficiently fast to be applied in tactical planning where no real time response times are required. Secondly, value results are presented. All value results are indexed focusing on comparing results and to ensure confidentiality of industry data. Initially, the value plan with total profits and single values in sales, distribution, production and procurement is analyzed. 

The refractive index is an important quantity for characterizing the structure of polymers. This is because it depends sensitively on the chemical composition, on the tacticity, and - for oligomeric samples - also on the molecular weight of a macromolecular substance. The refractive indices (determined using the sodium D line) of many polymers are collected in the literature. In order to characterize a molecule s constitution one requires knowledge of the mole refraction, Rg. For isotropic samples, it can be calculated in good approximation by the Lorentz-Lorenz equation ... 

In contrast to the crown ether 28, the cryptand K211 (33) is very beneficial to the control of MMA polymerization initiated by diphenyhnethyllithium in THF at —78 °C. As a result, PMMA with a very low polydispersity index (1.01) was obtained" . The effect of this ligand on the unimeric model, e.g. MiBLi, was studied by NMR spectroscopy. The equilibrium commonly observed in THF between tetramers and dimers is actually shifted towards a monomeric complexed species" . Both the E/Z molar ratio (90/10 instead of 0/100) and the chain tacticity (Table 5) are affected by the cryptand K211 (33) whatever the solvent used ". ... 

Analysis and Characterization. Gas chromatography was performed with a Hewlett-Packard model 5880A equipped with capillary columns and a flame-ionization detector. Gel permeation chromatography was performed with a Hewlett-Packard HPLG model 1090A with a refractive index detector. Tacticity determinations were conducted with an F-19 nuclear magnetic resonance (NMR) spectrophotometer (Varian XL-100) at 94.12 MHz for triad analyses (13). Inherent viscosity measurements were performed in 2-butanone at 25.0 °C. 

With this much interest in polyethylene, many attempts have been made to use low frequency NMR in either the time domain or frequency domain to monitor and control the production more rapidly. Auburn International (now part of Oxford Instruments) developed a widely adopted system based on the time domain spectrometers [21]. In this case, sample preparation is no longer an issue since the system accepts either powder or pellets and no solvent is used. The Auburn systems determine crystalline and amorphous ratios, viscosity, melt index and molecular weight For other types of polymers, the list of advertised measurements include tacticity, rubber content, copolymer analysis, and various rheological properties. These values are determined by correlating several routine but laborious methods with the decay of the NMR signal under various pulse sequences. The man-hours... 

Contents Introduction. - Activation and Coupling. - Reversible Blocking of Amino and Carboxyl Groups. - Semipermanent Protection of Side Chain Functions. - Side Reactions in Peptide Synthesis. - Tactics and Strategy in Peptide Synthesis. - Techniques for the Facilitation of Peptide Synthesis. - Recent Developments and Perspectives. - Author Index. - Subject Index. 

The crystallinity tends to rise with increasing the tacticity and melt flow index (MFI) of PP. The opposite occurs by copolymerization with... 

Ke5Words cluster index, comonomer distribution, monomer dispersity, NMR, H NMR, NMR, tacticity, sequence length, copol3uner. 

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