Tacticity control

There are a few exceptions to this general rule. One of the few examples of an effect on polymer stereochemistry was provided by Dais et al.m who found that polymerization of 31 above the cmc initiated by y-irradiation at 25 °C yields polymer composed entirely of syndiolaclic dyads P(m) =0. When the double bond was distant from the polar head group in 32, the tacticity observed was similar to that observed in solution polymerization / ( )-0,18. Polymerization of 31 at higher temperatures (50 °C) initiated by AIBN also showed no sign of tacticity control. The stcrcospccific polymerization of 31 was attributed to organization of the methacrylate moiety on the surface of the micelle. 

The algorithm also incorporates tacticity control for vinyl chains. The random number generator is used to choose between d- and l-versions of the transformation matrix. A single parameter controls the relative probability of d- and l-residues. The poly(p-fluorostyrene) results presented here are for atactic (stereochemically irregular) chains. 

The control process, providing the steering for the tactical control level. 

Nowadays, these hierarchical levels are still used to explain the control structure in an organization. Van Mai (Mai van, 1999) uses the terms operational control level, tactical control level and strategic control level, for the technical, managerial and institutional level respectively. The terms used by van Mai will be used in the remainder of this thesis. 

The three hierarchical levels are interconnected by information flowing from the strategic level via the tactical level to the operational level, and the other way around. From upper to the lower level, the information flow is related to the environment on the strategic level, which is the organizational values and norms. However, as Thompson (Thompson, 1967) identified, the tactical control level can allow the operational level to operate as a relatively closed system. The tactical level provides a buffer between the uncertain environment and stability of resources required for uninterrupted production on the operational level. In this way the influences from the external environment on the operational level will be reduced to a minimum. The information flow going from lower to upper level is related to the operational process or transformations. The top down flow provides the restrictions and conditions for the transformation, while the bottom up flow provides information about the status of inputs, outputs, and resources of the transformations. The horizontal information flows are between different control elements on one hierarchical control level. 

The ineffective observation element on the tactical control level, as identified in the previous stage, is analysed in more detail by retrieving the types of causal latent conditions, contributing to the ineffectiveness. 

The SMS is lacking especially on tactical control level, where a number of safety directives are not followed effectively and the consequences of deviations are only analysed for time constraints. Improving the observation and judgement element on the tactical control level can be achieved by addressing the latent conditions. 

Because, for each of the three cases, 20 precursors are analysed, a comparison between the results of all three cases is possible. From the results of the analysis it appears that in all three cases, most precursors were enabled by the ineffective judgement element on the tactical control level. In companies A and B, the judgement element on the operational control level is the ineffective control element enabling the second most frequent precursors, while for company C the judgement element contains the most precursors on the strategic control level and appears to be a critical element at each control level for all three companies. Moreover, relatively more ineffective control elements are present on the higher (tactical and strategic) control levels in company C (18), than in company A (12) and B (11). 

Efficient and defect-free folding of the polymer will, at least, require a control of the regioselectivity of monomer incorporation and polymer tacticity. If, for example, the degree of tacticity control is poor, the stereochemical defects are irreversibly incorporated into the polymer, and the subsequent folding may fail or produce defective structures. By contrast, dynamic self-assembly may allow defects to be corrected and the hierarchical structure to be controlled or fine-tuned using external parameters (solvent, additives, temperature) prior to covalent fixation by polymerization. 

Finally, the stereoselectivity of most cationic vinyl polymerizations is poor due to the sp2 hybridization of carbenium ions at carbon. In this case, attack from either side of the plane has approximately equal probability leading to similar proportions of meso and racemic diads. For the sufficiently bulky substituent(s) tacticity control improves for example, highly syndiotactic (>90%) poly(a-methylstyrene) can be prepared by cationic polymerization (70]. 

Figure 5.15. Mechanism involved in Ziegler-Natta polymerization for tacticity control over the growing polymer chain.

Lewis acids are known to form complexes both with monomers and with propagating species. Their addition to a polymerization medium, even in catalytic amounts, can bring about dramatic changes in rate constants in homopolymerization (Section 8.3.4.1) and reactivity ratios in copolymerizalion (Section 8.3.4.2). Early work in this area has been reviewed by Bamford and Barton and Borsig. fhere is significant current interest in using Lewis Acids in establishing tacticity control in homopolymerization (see 8.3.4.1). 

Scheme 28. Enantiomorphic-Site Tacticity Control in ROMP...

CFAC Combined Forces Air Component (tactical control of all OPC aircraft operating... 

The Combined Forces Air Component (CFAC) was tasked with exercising tactical control of all OPC aircraft operating in the Tactical Area of Responsibility (TAOR) and operational control over Air Force aircraft. The CFAC commander exercised daily control of the OPC flight mission through a Director of Operations (CFAC/DO), as well as a ground-based Mission Director at the Combined Task Force (CTF) headquarters in Incirlik and an Airborne Command Element (ACE) aboard the AWACS. 

Tactical control involves a fairly limited scope of authority, that is, the detailed and usually local direction and control of movement and maneuvers necessary to accomplish the assigned mission. Operational control, on the other hand, involves a broader authority to command subordinate forces, assign tasks, designate objectives, and give the authoritative direction necessary to accomplish the mission. 

AWACS), U.S. Air Force (USAF) airlift, and the fighter forces. He had tactical control of the U.S. Army, U.S. Navy, Thrkish, French, and British fixed wing and helicopter aircraft. The splintering of control between the CFAC and MCC commanders, along with communication problems between them, were major contributors to the accident. 

The TAOR controller provided threat warning and tactical control for all OPC aircraft within the TAOR. 

Inaccurate Mental Models CFAC, and thus the Mission Director and ACE, exercised ultimate tactical control of the helicopters, but they shared the common view with the AWACS crew that helicopter activities were not an integral part of OPC air operations. In testimony after the acddent, the ACE commented, Hie way I understand it, only as a courtesy does the AWACS track Eagle Flight. ... 

Roles and Responsibilities The MCC had operational control over the Army helicopters while the CFAC had operational control over fixed-wing aircraft and tactical control over all aircraft in the TAOR.The Combined Task Force commander general (who was above both the CFAC and MCC) had ultimate responsibility for the coordination of fixed-wing aircraft flights with Army helicopters. 

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