Tacticity interpretation

Kim and Somorjai have associated the different tacticity of the polymer with the variation of adsorption sites for the two systems as titrated by mesitylene TPD experiments. As discussed above, the TiCl >,/Au system shows just one mesitylene desorption peak which was associated with desorption from low coordinated sites, while the TiCl c/MgClx exhibits two peaks assigned to regular and low coordinated sites, respectively [23]. Based on this coincidence, Kim and Somorjai claim that isotactic polymer is produced at the low-coordinated site while atactic polymer is produced at the regular surface site. One has to bear in mind, however, that a variety of assumptions enter this interpretation, which may or may not be vahd. Nonetheless it is an interesting and important observation which should be confirmed by further experiments, e.g., structural investigations of the activated catalyst. From these experiments it is clear that the degree of tacticity depends on catalyst preparation and most probably on the surface structure of the catalyst however, the atomistic correlation between structure and tacticity remains to be clarified. 

B. Measurement of Property Distributions for Copolymers. Figure 12 shows chromatograms of typical products in the copolymerization study (Column Code B2). Since the detector is responding to concentration, composition, and periiaps sequence length, the direct single detector interpretation as described for PMMA is not immediately applicable here. Tacticity variation is yet another consideration but ]s assumed of sa ond order importance for th samples (22). 

This is a tactic of interpreting an entity by adopting the presupposition that it is an approximation of the ideal of an optimally designed (i.e. rational) self-regarding agent. No attempt is made to... 

To clarify the tacticity problem, trans-l,4-hexadiene and 5-methyl-l,4-hexadiene polymers were examined by X-ray diffraction. Fiber diagrams were obtained from samples stretched to four times their original lengths. Eight reflections from the poly(trans-1,4-hexadiene) fiber pattern may be interpreted on the0basis of a pseudo-orthorhombic unit cell with a = 20.81 + 0.05 A b =... 

The same type of addition—as shown by X-ray analysis—occurs in the cationic polymerization of alkenyl ethers R—CH=CH—OR and of 8-chlorovinyl ethers (395). However, NMR analysis showed the presence of some configurational disorder (396). The stereochemistry of acrylate polymerization, determined by the use of deuterated monomers, was found to be strongly dependent on the reaction environment and, in particular, on the solvation of the growing-chain-catalyst system at both the a and jS carbon atoms (390, 397-399). Non-solvated contact ion pairs such as those existing in the presence of lithium catalysts in toluene at low temperature, are responsible for the formation of threo isotactic sequences from cis monomers and, therefore, involve a trans addition in contrast, solvent separated ion pairs (fluorenyllithium in THF) give rise to a predominantly syndiotactic polymer. Finally, in mixed ether-hydrocarbon solvents where there are probably peripherally solvated ion pairs, a predominantly isotactic polymer with nonconstant stereochemistry in the jS position is obtained. It seems evident fiom this complexity of situations that the micro-tacticity of anionic poly(methyl methacrylate) cannot be interpreted by a simple Bernoulli distribution, as has already been discussed in Sect. III-A. 

Barriers to rotation about Mt=C have been measured by observation of NMR coalescence temperatures123,330,331. In some cases these are sufficiently high that epimerization by rotation about Mt=C is unlikely to be important, but in other cases such a process may be as fast as or faster than the propagation step. More detailed considerations show that when both cis and trans double bonds are formed in accordance with the enantiomorphic sites model then the cis junctions will always be associated with r dyads, and trans junctions with m dyads27,332. This model thus correctly predicts the observed tacticities in the first, third and fifth groups of results listed in Table 7. Cases of intermediate tacticity can also be interpreted in terms of this model if it is modified to include partial epimerization of P/ and Pr between propagation steps. 

This is interpreted in terms of a mechanism involving an equilibrium between the syn and anti rotamers of the initiator, in which the conversion of the dominant syn rotamer into the minor anti rotamer is rate-determining at high [M], with it = 6.1 x 10 5 s 1, while at low [M] the addition of M to the anti rotamer becomes rate-determining305. The value of k agrees well with the value determined directly in toluene by photochemical displacement of the equilibrium between the rotamers121,122. The tacticity of this polymer is mentioned in Section VIILA.5. 

He was conscious that what he was studying so slavishly was the past. Only a matter of a microsecond into it, but the past all the same. Each vehicle relayed its position and sensor data to Command, where they could all be interpreted and transposed on to the artificial landscape of the tactical display. If there were any surprises waiting for them, Mogushestvo would be able to react and issue commands as nearly instantaneously as made no difference. 

The multiple tactics and pragmatic efforts to improve interpretation (Knudson et ah, 1995) can be understood from within the mindfulness model (Alt Shaw, 1984 Bitgood et ah, 1988 Borun Adams, 1991). There are recurring recommendations in the interpretive texts to attend to the communication factors and visitor factors cited in the model. In addition, its applicability can be seen as working in all types of interpretation, both personal and in settings where the visitor is supported by non-personal mechanisms. 

In proton spectra of polymers knowledge of the exact values of the coupling constants and the chemical shifts makes it possible to simulate the experimental spectra by computer calculations. In this way it is possible to interpret quantitatively the complex spectra of many homopolymers and copolymers in terms of configuration (or "tacticity") and monomer sequences (copolymers). The obtained sequence lengths can be directly related to the polymerisation mechanism. 

Figure 26.2 is a flowchart of appropriate, safe, effective, and efficient use of medications in the hospital setting (12). It incorporates the role of the prescriber, nurse, pharmacist, and patient in a typical inpatient environment. It also depicts the role of the organization s pharmacy and therapeutics committee and quality improvement functions, which will be discussed later in this chapter. The decision to treat a patient in a hospital or extended-care facility typically adds a nurse or other healthcare provider (respiratory therapist, etc.) to the trio described in the ambulatory care setting. Every time that individual has to read, interpret, decide, or act is yet another opportunity for a mistake to occur. Each of the steps in the medication use process provides an opportunity for correct or incorrect interpretation and implementation of the tactics that support the therapeutic plan. With this many opportunities for medication misadventures to occur, it is easy to understand why tracking and improving quality are important aspects of medication use. 

Until recently, knowledge of the tertiary structure has been prerequisite for a meaningful interpretation of data derived from mutagenesis experiments, primarily because of the nature of the questions posed. Nevertheless, there are situations where more intuitive tactics can lead to valuable insights, as illustrated by a collection of selected examples. 

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