Tacticity living polymerization

These (BDI)ZnOR complexes yield a molecular weight up to 200,000 g/mol by full conversion, and comparably short reaction times of up to 2 days. This reaction proceeds under mild conditions giving narrow PD (1.1-1.2), and the reported proportional ratio between conversion and molecular weight throughout the reaction is consistent with a living polymerization in solution as well as in bulk [34,79]. Though several substitutions were carried out, no (BDI)Zn catalyst was found to generate tactic materials (Fig. 25). 

Block Copolymerization Cationic Polymerization Polymer Stereochemistry Tacticity Coordination Polymerization Living Radical Polymerizations... 

The chain tacticity of PMMA synthesized by GTP catalyzed by nucleophiles at different temperatures was analyzed by Webster and coworkers The syndiotactic content increases from 50% at 60 °C up to 80% at —90°C in THF, using tris(dimethylamino)sulfonium bifluoride [(Me2N)3S+ HF2 ] as catalyst . In contrast to the anionic polymerization of MMA, the stereoselectivity of GTP is less sensitive to solvent. It must be noted that PMMA is less syndiotactic when the GTP is catalyzed by nucleophiles rather than by Lewis acids . GTP was extended to the living polymerization of many acrylates and methacrylates, such as nBuMA, glycidyl-MA, 2-ethylhexyl-MA, Me3SiOCH2CH2-MA, sorbyl-MA, allyl-MA, lauryl-MA), acrylates (EA, BuA), acrylonitrile, methacrylonitrile and Al,A-dimethylacrylamide . 

Syndiotactic poiy(methyl methacryiate) Anionic living polymerization Mn = 2000 14500 M /Mn = 1.13-5.5 effect of synthetic variables on tacticity, molecular weight and distribution and yield discussed. [139,147]... 

In chain reactions the different types of monomers can be added subsequently to an active chain end. The most important techniques here are sequential living polymerization techniques, such as anionic or cationic polymerization. Certain metallocenes can be used in coordination polymerization of olefins leading to stereo block copolymers, like polypropylene where crystalline and amorphous blocks alternate with each other due to the change of tacticity along the chain [34]. In comparison to living polymerization techniques, free radical and coordination polymerization lead to rather polydisperse materials in terms of the number of blocks and their degree of polymerization. 

The anionic polymerization of NIPAM derivatives having an LCST has also been examined in detail [63]. Because these monomers had no acidic amide protons, the living polymerization proceeded easily in comparison with NIPAM, and the influence of tacticity, etc., has been examined. 

These two rotamers, whose reactivity and relative ratio is governed by the electronic nature of the alkoxide ligand, are responsible for the structure of the final ROMP-derived polymer. The rates of interconversion between these two rotamers strongly depend on the alkoxide. The living polymerizations tri ered by Mo-bis(tert-butoxide)-derived initiators usually lead to the formation of all-tram, highly tactic polymers. Tacticity of such polymers is believed to be controlled by the chirality of the alkylidenes, P-carbon (chain end control). 

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