Classes of polymerizations

Important classes of polymeric flow processes are described by time-dependent differential equations. The most convenient method for solution of the time-... 

Ionic polymers are a special class of polymeric materials having a hydrocarbon backbone containing pendant acid groups. These are then neutralized partially or fully to form salts. lonomeric TPEs are a class of ionic polymers in which properties of vulcanized rubber are combined with the ease of processing of thermoplastics. These polymers contain up to 10 mol% of ionic group. These ionomeric TPEs are typically prepared by copolymerization of a functionalized monomer with an olefinic unsamrated monomer or direct functionalization of a preformed polymer [68-71]. The methods of preparation of various ionomeric TPEs are discussed below. 

Table 10.44 Classes of polymeric cationic agents for aftertreatment of dyed cellulosic fibres [448]...

Recently, the Okada group described a new class of polymerization systems [43] oligoglycopeptide-type sugar-balls were obtained by a radial growth polymerization (RGP) of a-amino acid AT-carboxyanhydrides with PAMAM dendrimers of different generations. 

Some 17 years later, many of these predictions are turning into experimental reality as many of these questions are being answered in each new publication or patent that appears on dendritic architecture. Presently, dendritic polymers are recognized as the fourth major class of polymeric architecture consisting of three subsets that are based on degree of structural control, namely (a) random hyperbranched polymers, (b) dendrigraft polymers and (c) dendrimers (Figure 6). 

J.P. Garcia-Sandoval. Nonbnear robust control for a class of polymerization reactors. Master s thesis, Universidad de Guadalajara, Mexico, 2003. 

Diblock copolymers represent an important and interesting class of polymeric materials, and are being studied at present by quite a large number of research groups. Most of the scientific interest has been devoted to static properties and to the identification of the relevant parameters controlhng thermodynamic properties and thus morphologies [257-260]. All these studies have allowed for improvements to the random phase approximation (RPA) theory first developed by Leibler [261]. In particular, the role of the concentration fluctuations, which occur and accompany the order-disorder transition, is studied [262,263]. 

Amphiphilic polymers studied thus far for this purpose can be broadly classified into amphiphilic block copol5mers and amphiphilic homopolymers. We will discuss both of these types of linear polymer architectures. Another interesting class of polymeric amphiphiles is based on branched architectures, known as dendrimers. The most interesting aspect of dendrimers is that their molecular weight and polydisper-sity can be precisely controlled hence, these systems have the potential to be moved... 

In general, there are two distinctively different classes of polymerization (a) addition or chain growth polymerization and (b) condensation or step growth polymerization. In the former, the polymers are synthesized by the addition of one unsaturated unit to another, resulting in the loss of multiple bonds. Some examples of addition polymers are (a) poly(ethylene), (b) poly(vinyl chloride), (c) poly(methyl methacrylate), and (d) poly(butadiene). The polymerization is initiated by a free radical, which is generated from one of several easily decomposed compounds. Examples of free radical initiators include (a) benzoyl peroxide, (b) di-tert-butyl peroxide, and (c) azobiisobutyronitrile. 

Because of the complexity of the problems discussed, the theoretical approaches and interpretation of results presented by various authors and schools may be somewhat different. It may be hoped, however, that a confrontation of ideas may positively contribute to the knowledge about this important class of polymeric materials. 

There are two characteristic classes of polymerization process, those of step growth and of chain growth.73 In the former, monomers combine to form dimers, and dimers to form tetramers and all oligomers of intermediate size combine to form larger molecules at random. In this kind of process, typical of classical, equilibrium-condensation polymerization, products of high molecular weight are obtained at very high conversion only. 

For certain classes of polymerization, such as simple copolymerization, a similar generalized analysis could be derived from considerations of monomer reactivity ratios. However, in the completely general case (such as assembly of a protein from subunits) it would require knowledge of stoichiometries to specify these ratios, and it is just these stoichiometries that one is attempting to obtain from this analysis. 

The studies of the stability of heparin-amine complexes demonstrated that the stability of this class of polymeric materials might be improved by choosing the right amine. Quaternary ammonium salts were shown to bind heparin stronger than primary, secondary, and tertiary amines, while amines containing alicyclic or aromatic fragments are more efficient than the aliphatic ones. Of the quaternary ammonium... 

Another class of surfactants that are used in cosmetics and personal care products is the phosphoric acid esters. These molecules are similar to the phospholipids that are the building blocks of the stratum corneum (the top layer of the skin, which is the main barrier for water loss). Glycerine esters, in particular, triglycerides, are also frequently used. Macromolecular surfactants of the A-B-A block type [where A is PEO and B is polypropylene oxide (PPO)] are also frequently used in cosmetics. Another important naturally occurring class of polymeric surfactants is the proteins, which can be used effectively as emulsifiers. 

Asymmetric star polymers are megamolecules [1] emanating from a central core. In contrast to the symmetric stars very little was known, until recently, about the properties of the asymmetric stars. This was due to the difficulties associated with the synthesis of well-defined architectures of this class of polymeric materials. The synthesis, solution and bulk properties, experimental and theoretical, of the following categories of asymmetric stars will be considered in this review ... 

The analysis of the existing data suggest that polynuclear PCMU represent one of the least studied classes of polymeric chelates with the methods of production being in their infancy. In this respect we should pin our hopes on the method suitable for the polymerization of polynuclear MCM, the development of which is restricted by problems with their synthesis. 

There are two main classes of polymeric support utilized in the preparation of stationary phases for all modes of chromatography, namely silica and polystyrene-divinylbenzene copolymer. For simplicity, from this point on, the former will be referred to as silica and the latter class as polymeric. 

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