Radical ring-opening template polymerization

The radical ring-opening elimination polymerization of 4-methylene-l,3-dioxolane stimulated us to construct a novel template polymerization (3). The concept is that polymers bear polymers. Polymer-supported monomer, which had a structure of 2,2-dipheny 1-4-methylene-1,3-dioxolane, reacted with radical species to afford polyketone and copolymer of styrene with vinylbenzophenone as newborn polymer and template, respectively (Figure 12). These polymers were easily separated by fractional precipitation without any particular chemical treatment after polymerization. On the other hand, common template polymerization requires annoying procedures for the separation of obtained polymers form template. On this point, our novel template polymerization system differs from conventional template polymerization. 

Figure 12. Template polymerization by radical ring-opening polymerization.

The template processes can be realized as template polycondensation, polyaddition, ring-opening polymerization, and ionic or radical polymerization. These types of template polymerization are fundamentally treated in the separate chapters below. 

There is far less information in the scientific literature about template copolymerization than about template homopolymerization. As in the case of template homopolymerization, template copolymerization can be realized according to different types of reaction stepwise (template polycondensation), copolyaddition, radical or ionic polymerization, ring-opening copolymerization, etc. 

In contrast to template polycondensation or ring-opening polymerization, template radical polymerization kinetics has been a subject of many papers. Tan and Challa proposed to use the relationship between polymerization rate and concentration of monomer or template as a criterion for distinguishing between Type I and Type II template polymerization. The most popular method is to examine the initial rate or relative rate, Rr, as a function of base mole concentration of the template, [T], at a constant monomer concentration, [M]. For Type I, when strong interactions exist between the monomer and the template, Rr vs. [T] shows a maximum at [T] = [M]q. For type II, Rr increases with [T] to the critical concentration of the template c (the concentration in which template macromolecules start to overlap with each other), and then R is stable, c (concentration in mols per volume) depends on the molecular weight of the template. 

Sugiyama and co-workers (69,70) report a very interesting template process by the ring-opening polymerization induced by radicals. The polyethylene template was connected with 2,2-diphenyl-4-methylene-l,3-dioxolane groups by the covalent bonds. The process can be illustrated by the following reaction ... 

In radical polymerization usually in addition to the main elementary processes (initiation, propagation, and termination), we have the usual chain transfer to the monomer or to the solvent - changing the molecular weight of the product obtained - and also chain transfer to the polymer leading to the branched polymer. In ring-opening polymerization, many additional reactions can take place between monomer, solvent, and template depending on the chemical structure of the substrates. 

The special polymerization process in which specific interactions between template macromolecules and growing chains exist is called template polymerization. The process, as described in the chapter, can proceed by the mechanism of a chain reaction as radical, ionic, or ring-opening polymerization or as a step-growth process like polycondensation. 

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