Conversion Coordination polymerization

Coordination polymerization is the most versatile method of preparing PCL and its copolymers, affording high molecular weights and conversions, and either block or random copolymers depending on the conditions. As with the preceding classes of initiators, the product... 

Priftis et al.used titanium alkoxide catalyst-functionalized MWCNTs for the surface-initiated titanium-mediated coordination polymerizations of L-lactide (LEA), e-caprolactone (e-CL) and n-hexyl isocyanate (HIC) at 120 °C, room temperature and 130 °C in toluene for 24 h, 20 h and 20 h, respectively. The grafted PLEA content could be controlled by the reaction time. In contrast with the other two monomers, HIC had very low conversions. 

For a monodisperse polymer sample, d = 1. The ranges of d values change drastically with the different mechanisms of polymerization. The values of d are 1.01-1.05 in living polymerization (anionic, cationic, living free radical, etc.), around 1.5 in condensation polymerization or coupling termination of polymerization, around 2 in disproportionation reactions on polymerization, 2-5 for high-conversion olefins, 5-10 in self-acceleration on common free radical polymerization, 8-30 in coordination polymerization, and 20-50 in branching reactions on polymerization. 

To improve the characteristics of coordination polymerization catalysts, the combinations of different metal derivatives have been investigated. The association of zinc chloride to aluminum alcoholates improves the reactivity significantly and results in higher conversions (see Table 9). However, two polymer fractions are still obtained an isotactic and crystalline polymer of high molar mass and an amorphous and atactic polymer (mole fraction of isotactic dyads is less than 0.6). In contrast to AIR3/H2O or ZnR2/H20, the latter consists of regular head-to-head and tail-to-tail enchainments. ... 

Anionic and anionic coordination polymerizations of epoxides are often slow processes that require long reaction times to achieve high monomer conversions. Moreover, as reported in previous sections, a majority of these polymerizations suffer from side reactions, illustrated by the chain transfer reaction to monomer in alkali metal anionic polymerization and by a very low initiation efficiency and the formation of several polyether populations in coordination polymerizations. 

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