Catalytic CTA

The synthesis of numerous macromonomers can be performed by two methods through radical polymerization in the presence of various addition-fragmentation CTAs [292-295] or catalytic CTAs [69,70,296]. 

In a similar way, Norman et al. [331] synthesized PMMA oligomers by ATRP. The methacrylic double bond of the resulting macromonomer was directly obtained by elimination of the terminal halogen by catalytic CTAs, such as 5,10,15,20-lclraphcnyl-21 Lf,23f/-porphine cobalt(II) [Co(tpp)]... 

The prafoimance of foe catalyst for foe CTA hj hopurification was evaluated in a batch autoclave r ictor under conditions similar to those in the indtistry. 90g of CTA containing about 3000 ppm o f 4-CBA and 240 ml of water were chaigrf to foe reactor with Ig catalyst loaded. Hydropurification of foe CTA was conducted at 280ti in foe reactor under stirring (800 rpm) and 0.7 MPa hydrogen pressure. Samples takra after 0.5 h of reaction were analyzed with HPLC [4]. The catalytic performance of foe Pd/CNF catalyst was characterized by 4-CBA s conversion. 

Preparation conditions of Pd/CNFs by wet impregnation method, such as palladium precursor, impregnation time, calcinations and reduction, are proved to have profound effect on the catalytic property. The catalyst prqjared by impregnating HzPdCLi precursor in an hour, then calcinated in air and reduced in 20%H2/Ar is believed to perform better in CTA hydropurification than the industrial Pd/C under laboratory conditions. 

Crude terephthalic acid (1,2,3) CTA is produced by catalytic oxidation of p-xylene with air in the liquid phase using acetic... 

Scheme 63 Several CTAs synthesized by catalytic chain transfer...

Two genes (Pcytla and Pcytlb) encode distinct isoforms of CT, a, and p, respectively. The CTa gene spans approximately 26 kb. Exon 1 is untranslated, exon 2 encodes the translation start site and a nuclear localization signal, exons 4-7 encode the catalytic domain, exon 8 encodes the alpha helical membrane-binding domain, and exon 9 encodes... 

Chain transfer with CoPhBF acting as the CTA is a catalytic process. The reaction mechanism is represented by Scheme 4.4 below [50, 54]. 

Coordinative chain transfer polymerization (CCTP, also called catalytic chain transfer polymerization) is typically a process that comprises a chain transfer step that must be i) reversible and ii) much faster than propagation. The growing polymer chain is exchanged between a CTA and the catalyst when attached to the CTA, it is just a dormant chain, whereas propagation takes place on the catalyst (Scheme 27.1). As a consequence, if the CTA is in excess, several macromolecular chains can be produced per catalyst molecule, and ideally (if the transfer rate is not determining), all chains will have the same length. 

Reversible and fast chain transfer is a prerequisite in order to control a polymerization process. In this regard, relative amount and synergy between each catalytic partner, that is, precatalyst and cocatalyst/CTA, are of primary importance. This was the case with ethylene, which has been by far the most studied monomer in this frame, as shown by Gibson [9] with Fe/Zn catalysts, after the pioneering studies of Mortreux [8] with Ln/Mg and more recently Kempe with Y/Al systems [40]. 

Zhang, D., Murata, Y., Kishikawa, K., et al. (2008). Synthesis of Large Surface Area MnOx-Ce02 Using CTA and its Catalytic Activity for Soot Combustion, J. Ceram. Soc. Japan, 116, pp. 230-233. 

To control molecular mass, CTAs may be used. The chemically controlled transfer reaction of dodecyl mercaptan in homo- and copolymerizations of styrene and MMA is not influenced by the presence of up to 40 wt.% C02. On the other hand, the diffusion-controlled catalytic chain-transfer reaction of Co complexes was enhanced by up to 1 order of magnitude depending on the reaction conditions, in particular on CO2 content amd the Co complex used. ... 

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