Pseudoliving

A study of the polymerization kinetics of methyl methacrylate, in the presence of PBN, and of molecular-mass properties of the obtained polymers shows that the systems react by the pseudoliving mechanism (699). In the first stages of the polymerization process, PBN reacts with oligomeric radicals, forming stable nitroxyl radical-spin adducts A-, see Scheme 2.207. 

Therefore, nitrones, being potential sources of stable radicals are able to participate directly in the growth stage of the polymer chain. In the case of nitrones the pseudoliving mechanism is realized at lower temperatures (50—60° C) then in the case of nitroxides (> 100° C). 

Below, the initiation step and mechanisms involved in telomerisation are described, followed by the various processes used, the telogens, the monomers and their respective reactivities. The following part deals with the pseudoliving radical telomerisation of fluorinated monomers and finally different applications of fluorinated telomers are given. 

Nearly at the same time, Johnson and Young reported a similar system for the polymerization of -butyl vinyl ether with iodine, and called the process a pseudoliving polymerization [55], Also, Pepper suggested that the active centers in polystyrene derived from perchloric acid might have a long lifetime at a very low temperature [32,50], and later obtained block copolymers of styrene with /< r/-butylazyridine by a sequential polymerization from the perchlorate-initiated polystyrene end [56]. 

Research over the past 30 years has produced a large number of ROMP polymers, and virtually all of these polymerizations have been reviewed elsewhere. The most recent work has revolved about the living or pseudoliving nature of ROMP polymerization, and a few words regarding this chemistry are worth mentioning here. 

The pseudoliving character of PO anionic polymerisation produces a large variety of block copolymers, by simply changing the nature of the oxirane monomer because the catalytic species (potassium alcoholate) remains active during and after the polymerisation reaction. Thus, if a polyether is synthesised first by anionic polymerisation of PO and the polymerisation continues with another monomer, such as EO, a block copolyether PO-EO with a terminal poly[EO] block is obtained. Another synthetic variant is to obtain a polyethoxylated polyether first by the anionic polymerisation of EO initiated by glycerol [108], followed by the addition of PO to the resulting polyethoxylated triol. A block copolyether PO-EO is obtained with internal poly[EO] block linked to the starter. Another possibility is to add the monomers in three steps first PO is added to glycerol, followed by EO addition and finally by the addition of PO. A copolyether triol block copolymer PO-EO with the internal poly[EO] block situated inside the polyetheric chain between two poly[PO] blocks is obtained [4, 100, 101]. 

The block copolymer preparative techniques reviewed in this report include sequential addition to macroanions, "pseudoliving" carbenium ion systems, used of coordination catalysts, coupling of polymer termini, and various preparations employing free radical polymerization. The review covers 133 papers and patents. 

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