Polymer, chemical physics radical polymerization

Fig. 1 Representative methods of hydrogel formation. (A) Chemically cross-linked hydrogels are prepared from monomers, oligomers, or polymers in the presence of cross-linking agents. The chemical cross-linking proceeds via radical polymerization or polycondensation reaction. (B) Physically cross-linked hydrogels can be formed by ionic interactions, hydrophobic interaction, or hydrogen bonding.

Emulsion polymerization is the process of choice for the commercial production of many polymers used for coating and adhesive applications, especially for those products that can be used in latex form. Emulsion polymerization uses free-radical polymerization mechanisms with unsaturated monomers. The heterogeneous nature of the reaction mixture, however, has a significant influence on the chemical and physical reaction mechanisms and on the nature of the final product. 

The paper summarizes the basic results of our studies related to further development of known concepts of the chemical physics of polymers and creation of new ones in environment protection and life safety. The scientific novelty of our data is in development of the theory of radical-chain processes of polymer formation on the basis of exploring the gross kinetics of radical polymerization of vinyl monomers, estabhshment of the mechanisms of elementary reactions of chain initiation, propagation, and termination. 

The formation of polymer can be followed directly by isolation of the polymer as it is produced. This method has the advantage that the physical and chemical structure of the polymer can be studied as a function of conversion. In this method, the polymerization is terminated by adding suitable substances (inhibitors in free radical polymerization) or by quenching the reaction by cooling rapidly. The monomer and/or solvent can be distilled from the polymer, although often not all the monomer can be removed when the polymerizate viscosity is high. In addition, neither the initiator nor the catalyst is removed. A distillation must in any case be carried out at very low temperatures, since otherwise the polymer may be degraded or the polymerization may continue. 

Vinyl ester resins The vinyl ester resins are essentially epoxide resins, normally the digly-cidyl ether of bisphenol A, that have been reacted with acrylic acid or its derivatives. The unsaturation in the acid residues provides sites for a cross-linking mechanism based on free radical polymerization. The retention of the bisphenol A backbone in the chain of the cross-linked polymer conserves most of the mechanical and physical properties associated with the parent epoxy. The resins thus provide a combination of ease of processing with good chemical resistance and mechanical behaviour. 

Studying 3-D polymerization foresees an investigation of the total of all chemical and physical processes, useful properties of the pol3rmeric material and phenomena responsible for the formation of a polymer and, as a result, also for the formation of a complex. Therefore, knowledge of the structural and physical aspects of the microheterogeneous chemical mechanism of the 3-D radical polymerization is very important. 

Yarmukhamedova et al. in Chapter 7 of this volume investigate chemical physics properties of a class of aromatic compounds (diketocarboxylic acids) on the radical initiation properties of an initiator compound used in a polymerization reaction system. Thus as Yarmukhamedova et al. describe, the influence of aromatic diketocarboxylic acids on the decomposition initiator of radical polymerization - azobisisobutyronitrile was studied by U V spectroscopy. The interaction occurs with the participation of carboxyl groups of diketocarboxylic acids with nitrile groups of the initiator. It is shown that polymer obtained in the presence of aromatic diketocarboxylic acids has mainly a syndiotactic structure. And thus such work as that reported here by Yarmukhamedova et al. advances our imderstanding of the synthesis and properties of technologically important classes of radical polymerization polymers. 

After all this discussion about radical polymerization and new methods to develop processes to obtain better control of the polymerization, the question remains Why Why should one use these novel methods to polymerize vinyl monomers The answer that first comes to mind is supplementation of anionic and cationic polymerization as the primary means of obtaining well-defined (co)polymers, in these cases by radical polymerization processes which are more tolerant of impurities, functional groups and are applicable to a wider range of monomers. This increased level of control over radical polymerization will allow industry to tailor a material to the requirements of a specific application using the most robust polymerization process available, ensuring the polymers have the optimal balance of physical and chemical properties for a given application. 

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