Tacticity reviews

Microstructure. Interest in PVP microstmcture and the potential for tacticity has been reviewed (39,40). PVP generated by free radicals has been shown to be atactic except when polymerization is conducted in water. In this case some syndiotacticity is observed (40). In the presence of syndiotactic templates of poly(methacryhc acid) (or poly(MAA)), VP will apparentiy polymerize with syndiotactic microstmcture, although proof is lacking (41—45). The reverse, polymerization of MAA in the presence of PVP, affords, as expected, atactic poly(MAA) (46,47). 

The use of non-inert and chemically modified electrodes and other strategies for the detection of species that are difficult to analyze with the normal electrode materials have been reviewed.55 Photosensitization prior to amperometric detection is another tactic that has proved useful for the analysis of substances that are normally considered to be electrochemically inert.56 The use of pulsed amperometry has recently been reviewed.57... 

Stereoselective ROMP has been reported with monomer (213). Initiator (211) affords highly stereoregular polymer with >98% trans C=C bonds in the polymer backbone.534 However, when (210) is used, >98% cis-poly-(213) is obtained.535 A similar situation occurs for the diester monomer (214). Furthermore, a rapidly equilibrating mixture of (210) and (211) can be used to allow intermediate cis/trans contents to be manipulated by the stoichiometry of the initiator mixture. 13C NMR536 and dielectric analyses537 suggested that trans-poly-(213) is highly syndio-tactic (92% r dyad content). The ROMP of other fluorinated olefins has been recently reviewed.538... 

A few reviews have dealt with the identification of synthetic polymers by Py-GC/MS [76]. In addition to compositional studies, applications of pyrolysis to synthetic polymers include sequence length characterization in copolymers [77] and tacticity measurements in stereoregular homopolymers [78]. 

Most of the modeling procedures commonly used require that the model first be reduced to a form which is linear in the unknown parameters. This procedure represents very good tactics the technique will be exploited frequently in this review, particularly in Section V. If the scope of the models to be used or the range of experimental variables to be explored is not limited when applying this philosophy, the procedure also represents good modeling strategy. 

For these reasons, a proper balance must be achieved between the linearization tactics and the overall modeling strategy. Both linear and nonlinear methods will be illustrated in the review, along with the problems encountered when relying too heavily on either single approach. First, however, some of the more common linear procedures will be discussed. 

The interesting problems of ring-chain equilibria, cis/trans blockiness, head-to-tail bias, and the various methods used to determine tacticity are treated in detail in three reviews.158-160 Consequently, only some more interesting observations are discussed here. 

Section I. A complete review concerning all types of synthetic optically active polymers prepared up to now has been published by Schulz and Kaiser [Adv. Polymer Sci. 4, 236 (1965)]. The relations between tacticity and configurational asymmetry of optically active polymers have been discussed by Fueno, Shelden and Furukawa [T. Fueno, R. A. Shelden, J. Furukawa J. Polymer Sci., Part A, 3, 1279 (1965)]. 

Schmidt G, Wilhelm WE (2000) Strategic, tactical and operational decisions in multi-national logistics networks a review and discussion of modelling issues. International Journal of Production Research 38 1501-1523... 

This process serves three important purposes. First, it provides a fourth detailed review of the document. Second, it serves as practice for the FDA presentation meeting. And third, it provides an opportunity to discuss strategy and tactics. While this independent review is certainly not mandatory (it does not appear as even a suggestion in any FDA guidance document), it is a common practice and highly recommended. 

Another review [36] discusses the determination of composition and structure, including tacticity, branching and end groups for diene polymers with the help of IR spectroscopy. 

Several reviews of early work on topotactic polymerizations and isomeriza-tions are available, and the reader is referred to the summaries of Morawetz [88] and Gougoutas [8] for a more complete account. The earliest study of a topotactic reaction appears to have been the observation, in 1932, of the polymerization of trioxane to poly-oxy-methylene [89]. Similar polymerizations of tetraoxane [90] and of trithiane [91 ] have also been reported to show retention of crystallographic axes from the monomer lattice. Other examples are discussed below. The topo-tacticity of a reaction can be determined solely by x-ray crystallographic analysis at the reactant and product endpoints. Thus a simple classification of a reaction as topotactic tells very little about how the structure of the crystal lattice changed in the course of reaction. 

A low degree of tacticity is obtained because these monomer-orienting forces are quite weak. Thus, polymer stereoregularity is achieved only with certain suitable monomers and at low temperatures. Increased tacticity can be achieved in some cases by using monomer-orienting forces other than the catalyst or the polymer end groups, but these have rather limited utility (canal complexes, solid state polymerizations, etc.). Simple polymerization systems fall outside the scope of this review and are not discussed further. 

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