We report on an efficient route to design large macrocyclic polymers of controlled molar mass and narrow dispersity. The strategy is based on the synthesis of a triblock copolymer ABC, in which the long central block B is extended by two short A and C sequences bearing reactive antagonist functions. When reacted under highly dilute conditions, this precursor produces the corresponding macrocycle by intramolecular coupling of the A and C blocks. Chloroethyl vinyl ether was selected as the monomer for the central block B, because it can be readily derivatized into brushlike polymers by a grafting process. The corresponding macrocyclic brushes were decorated with polystyrene or randomly distributed polystyrene and polyisoprene branches. In a selective solvent for the polyisoprene branches, the macrocyclic brushes self-assemble into cylindrical tubes of up to 700 nanometers.
A new strategy for the synthesis of vinyl type macrocyclic polymers of controlled molecular weight and molecular weight distribution has been investigated. It involves the direct coupling of an ,heterodifunctional linear polymer precursor previously prepared by living polymerization. The cyclization is achieved under high dilution, by appropriate activation of one of the polymer ends in order to allow its reaction with the other end function. The theoretical advantages of this approach compared to the conventional procedure involving the coupling of a living homodifunctional polymer precursor by a difunctional organic molecule are discussed. This new technique has been applied to the synthesis of cyclic polystyrenes with high yields (>85-90%). The structural characterization of the polymers as well as some of their thermal properties is also reported.
The anionic polymerization of propylene oxide initiated by alkali metal alkoxide suffers from several drawbacks such as a slow polymerization rate in nonpolar solvents and an important chain transfer reaction to monomer. We found that the addition of trialkylaluminum to the alkali metal alkoxide/ propylene oxide system in hydrocarbon media strongly enhances the polymerization rate and strongly reduces the transfer reactions, thus allowing the controlled synthesis of poly(propylene oxide) with relatively high molar masses (up to 20 000 g/mol). At constant monomer and alkali metal alkoxide concentrations the polymerization rate increases with increasing trialkylaluminum concentration. Kinetic data and 1 H NMR studies indicate that the trialkylaluminum derivative is involved in the formation of two distinct complexes, one with the alkali metal alkoxide and another with the PO monomer. The strong electron-withdrawing on PO R-carbons associated with AlR 3 complexation makes the monomer much more susceptible to ring opening. Moreover, since the withdrawing effect is much less pronounced on the PO methyl group, the complexation also results in a higher selectivity of the nucleophilic species toward the ring-opening reaction to the detriment of the proton abstraction process yielding transfer to monomer.
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