Transfer of Catalyst

After a detailed study of the polymerization of 27a, four important points were clarified (1) the polymer end groups are uniform among molecules— one end group is Br and the other is H (2) the propagating end group is 

Regioregular polythiophenes with various side chains containing ether, ester, and thiol units had been synthesized, and showed interesting properties [330]. However, the polydispersity of these polymers was not con- 

McCullough and coworkers had synthesized block copolymers of poly(3-hexylthiophene) and polystyrene or PMA by ATRP of the vinyl monomer from a polythiophene macroinitiator, which was prepared in several steps 

It is important to clarify whether catalyst-transfer condensation polymerization is specific to polythiophene, or whether it is generally applicable to the synthesis of well-defined it-conjugated polymers. We investigated the synthesis of poly(p-phenylene), to see whether a monomer 28 containing no heteroatom in the aromatic ring would undergo catalyst-transfer polymerization. However, all polymers obtained in the polymerization with Ni(dppp)Cl2, Ni(dppe)Cl2, or Ni(dppf)Cl2 possessed low molecular weights and broad polydispersities. Nevertheless, we found that LiCl was necessary for opti- 

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The first moving-bed process employed countercurrent flow of catalyst and reactants in both vessels and used mechanical bucket elevators to transfer the catalyst from one vessel to the other. This process, originally developed by the Socony-Vacuum Oil Company, was named the Thermo-for Catalytic Cracking (TCC) process (239,295,339). Two major improvements were subsequently developed change from countercurrent to concurrent flow in the reactor (297,298) and substitution of a gas-lift system for transfer of catalyst. In the gas-lift system, the catalyst pellets are conveyed upward through a pipe, or pipes, by a stream of flue gas or air. 

Nowadays it is becoming common practice to bring multiple analytical techniques to bear on the characterization of catalysts. Very often bulk and surface analysis methods are combined to yield detailed complementary information. A typical scheme of catalyst parameters to be determined and of appropriate analytical methods has been presented by Delmon [ I). who reviewed the potential of surface analysis in the characterization of hydrodesulfurization (HDS) catalysts. This scheme, redrawn, is shown in Fig. 1. Unfortunately, due to certain inherent problems, the whole range of well-e.stablished surface spectro.scopic methods cannot be applied in every case. Another disadvantage is that the application of surface-specific spectroscopies requires the transfer of catalyst samples into vacuum, thus restricting the possibilities for genuine in situ surface analysis of working catalyst.s. 

Scheme 1 General scheme of chain-growth condensation polymerization via (1) change of substituent effect and (2) transfer of catalyst Ar aryl group, X halide, Y metal...

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