Ring-opening polymerization living character

In cationic ring-opening polymerization, there are not too many examples of the systems in which ratios of kplk, are known. In the polymerization of substituted aziridines and substituted thietanes the ratios of rate constants of chain transfer to polymer to the rate constants of propagation have been measured and at least the value obtained for polymerization of N-/-butylaziridine (1.2-104) [260], indeed indicates the living character... 

The necessary, but not sufficient criterion of the living character of polymerization is the possibility of preparation of high molecular weight polymers (M > 10s). This has been achieved in several systems in cationic ring-opening polymerization, e.g., in the polymerization of some cyclic ethers 3,3-bis(chloromethyl)oxetane, tetrahydrofuran, 1,3-dioxo-lane, and 1,3,5-trioxane. 

The living character of the ring opening metathesis polymerization described earlier in this review enables a simple preparation of functionalized norbornene-based monoliths. Adding one more in situ derivatization step that involves functional norborn-2-ene and 7-oxanorborn-2-ene monomers that react with the surface-bound initiator, the pores were provided with a number of typical functional groups such as carboxylic acid, tertiary amine, and cyclodextrin [58,59]. 

Ring-opening metathesis polymerization (ROMP) of substituted bicyclo octa-dienes or paracyclophane-enes initiated by Gmbbs molybdenum, tungsten-based carbenes have been used to prepare PPV s [178—181]. The living character of ROMP has been exploited to prepare soluble well-defined precursors, which can be converted into XI. Yu and Turner have used ROMP of tetra octyloxy-substituted paracyclo-phanedienes initiated by reactive ruthenium-based carbenes to prepare monodisperse, soluble yellow fluorescent PPV with an alternating cis-trans microstructure and molecular weights as calculated [178] (Fig. 9.21). 

A new synthetic method to prepare soluble phenyleneviny-lene polymers by the ring-opening metathesis polymerization (ROMP) of 4,7,12,15-tetraoctyloxy-[2.2]paracyclophane-1,9-diene was also presented under microwave irradiation (Figure 23). The polymerization showed a living character and gave polymers of controlled molecular weight, with a narrow polydispersity, fewer chain defects, and an alternating cis, trans-microstructure. 

These data clearly demonstrates the susceptibility of lactic acid derivatives towards selective transesterification with primary alcohols and confirms that secondary alcohols are dormant towards transesterification with the ring-opened products. Thus, the living polymerization character is a manifestation of the rapid initiation and the weakly nucleophilic... 

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