Factors influencing polymerization

Lower activities were attributed to reduced stability of the active species under polymerization conditions. The lower molecular weights of their products were explained to be the result of increased hydrogen transfer rates. Variations within the heterocyclic components of the ligand showed that both steric and electronic factors influence polymerization behavior of such catalysts. 

General Factors Influencing Polymeric Liquid Crystalline Materials... 

Hydrolysis and Polycondensation. As shown in Figure 1, at gel time (step C), events related to the growth of polymeric chains and interaction between coUoids slow down considerably and the stmcture of the material is frozen. Post-gelation treatments, ie, steps D—G (aging, drying, stabilization, and densification), alter the stmcture of the original gel but the resultant stmctures aU depend on the initial stmcture. Relative rates, of hydrolysis, (eq. 2), and condensation, (eq. 3), determine the stmcture of the gel. Many factors influence the kinetics of hydrolysis and... 

Figure 2. Factors influencing taste/odor of carbonated beverages in polymeric containers...

Of special meaning for ionic reactions like cationic polymerization is the consideration of the interaction between reactants and solvent. This was attained by use of the extended solvent continuum model introduced by Huron and Claverie 69,70). Specific interactions between molecule and solvent cannot be taken into account by this model. For the above reason, the solvent is not considered to be an interacting partner, rather as a factor influencing the reacting species (see part 2.3.4). 

These three factors influence the ability of the polymer to crystallise, the melting point of any resulting crystalline regions, and also the glass transition temperature. It is the last of these features of polymeric materials which we will concentrate on for the rest of this chapter. 

Cross-linking of polymers is done routinely by radiation technology. The factors influencing the cross-linking or the efficiency of cross-linking of polymeric materials are ... 

Throughout the text we will relate polymer structure to the properties of the polymer. Polymer properties are related not only to the chemical nature of the polymer, but also to such factors as extent and distribution of crystallinity, distribution of polymer chain lengths, and nature and amount of additives, such as fillers, reinforcing agents, and plasticizers, to mention a few. These factors influence essentially all the polymeric properties to some extent including hardness, flammability, weatherability, chemical stability, biological response, comfort, flex life, moisture retention, appearance, dyeability, softening point, and electrical properties. 

There are four main compartments a soluble macromolecule can enter the central compartment (blood and lymphatic system), interstitium, intestinal lumen, and lysosomes [100, 101]. Minor compartments are primary urine, liquor, bile, etc. There is no experimental evidence that clearly indicates the penetration of synthetic macromolecules into the cytoplasm, i.e, into the intracellular compartment (inside the cell but outside the endosomes or lysosomes) [101]. The movements of soluble macromolecules between body compartments have been extensively reviewed [14, 20,100-104] and will not be covered in detail here. We shall concentrate on the discussion of main factors influencing the movement of soluble macromolecules when administered into the bloodstream. Depending on the structure and molecular weight distribution, part of the polymeric molecules are excreted in the urine. Simultaneously, the macromolecules are cleared from the bloodstream by endocytosis. It is important to note that nonspecific capture of soluble macromolecules by the specialized cells of the reticuloendothelial system is generally much less (orders of magnitude) when compared to vesicular carriers of a comparable structure. 

Fig. 15 shows the way ionic factors influence these initiation, termination and transfer reactions. This shows the effects of electron releasing substituents on the electron availability for hydride transfer and for oxidation or electron deficiency for proton transfer and for reduction. Present knowledge allows an even less precise treatment here than for polymerization. 

Another factor that can influence polymerization rate is monomer concentration in the particles. This is a function of particle size the... 

Ghosez-Giese, A. and Giese, B. (1997) Factors influencing the addition of radicals to atkenes. In K. Matyjaszewski (Ed.) Controlled Radical Polymerization, ACS Symposium Series 685. American Chemical Society, Washington, DC, p. 50-61. 

Coates and co-workers reported polymerizations using both the enantiomerically pure (7) and the racemic (8) Ao-propoxide analogues [21], Complex 8 polymerized rac-lactide iso-selectively producing stereoblock PLA (P = 0.96). The isoselectivity was achieved due to the high selectivity of 7 for RR-lactide and corresponding S -enantiomer for S S -lactide. Further studies of the aluminium-salen system have led to the proposal that several factors influence the polymerization... 

Leszczynska, A., Njuguna, J., Pielichowski, K., and Banerjee, J. R. (a) Polymer/montmorillonite nanocomposites with improved thermal properties, Part I Factors influencing thermal stability and mechanisms of thermal stability improvement, Thermochim. Acta (2007), 453, 75-96. (b) Polymer/montmorillonite nanocomposites with improved thermal properties. Part II Thermal stability of montmorillonite nanocomposites based on different polymeric matrixes, Thermochim. Acta (2007), 454, 1-22. 

Sources Gawande (Nazare), S., Investigation and prediction of factors influencing flammability of nightwear fabrics, PhD thesis, University of Bolton, Bolton, U.K., 2002 Nazare, S. et al., Fire Mater., 26,191,2002 Horrocks, A.R. et al., Recent Advances of Flame Retardancy of Polymeric Materials, Vol. XI, Lewin, M. (Ed.), Proceedings of the 2000 Conference, Business Communication Company, Stamford, CT. a Rames extinguished when the flame was moved away. b Fabric melted away from the flame. c Test not performed. 

Copolymerization of styrene with diolefins provides further support that monomer coordinates with the cationic site prior to addition. Korotkov (218) showed that in homopolymerizations styrene is more reactive than butadiene, but in copolymerization the butadiene reacted first at its homopolymerization rate and when it was exhausted the styrene reacted at its homopolymerization rate. This interesting result has been duplicated by Kuntz (245) and analogous results have been obtained by Spirin and coworkers (237) for the styrene-isoprene system. Presumably, the diene complexes more strongly than styrene with the lithium and excludes styrene from the site. That the complex occurs at a cationic site, rather than at the anion or the metal-carbon bond, is indicated by the fact that dienes form more stable complexes than styrene with Lewis acids (246). It should be emphasized that selective monomer coordination is not the only factor influencing reactivities in copolymerizations. Of greatest importance are the relative reactivities of the different polymer anions. The more resonance-stabilized anion is more readily formed and is less reactive for polymerizing the co-monomer. 

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