Akihiro Yokoyama

Chiral amplification based on sergeants and soldier effect in helically folded poly(naphthalenecarboxamide) was reported. Copolymerization of chiral monomer and achiral monomer was carried out in the presence of phenyl 4-methylbenzoate as an initiator and lithium 1,1,1,3,3,3-hexamethyldisilazide (LiHMDS) as a base under several conditions. The copolymer obtained as the polymerization progressed was followed by GPC, and the chiral monomer unit ratio was estimated from the 1H NMR spectrum after purification of the products by HPLC. The ratios of the chiral monomer unit to the achiral monomer unit in the products remained almost constant during the polymerization, indicating that random copolymerization proceeded. The results show that strong cooperativity between the monomer units composing the helical structure would arise from the intramolecular self-association of the main chain of the poly(naphthalenecarboxide), driven by the solvophobic effect in the aqueous solvent system.

The synthesis of poly (naphthalenecarboxamide) with a chiral tri (ethylene glycol) side chain and their secondary structure in solution was discussed. The helical structure was confirmed by X- ray crystallographic analysis of oligo (N-methyl-p-benzamide), which revealed a helical conformation with three monomer units per turn in crystal and by exciton model analysis of CD spectra induced by the secondary structure of the polyamide. The UV and CD spectra in solution indicated that the polyamide adopts a one-handed helical conformation. The excitation model analysis of the UV and CD spectra indicated that poly (naphthalenecarboxamide) with a chiral tri (ethylene glycol) side chain has adopted a thermodynamically controlled right handed helical conformation in organic solvents. The folding of napthalene polyamide can be enhanced by a solvophobic effect and completed at 0-15 ° C in 70% water-methanol.

The development and applications of chain-growth condensation polymerization are reviewed. Well-defined aromatic polyamides, polyesters, and polyethers have been synthesized via substituent effect-assisted chain-growth condensation polymerization, in which the polymer propagating ends are more reactive than the monomers due to resonance or inductive effects between the functional groups of the terminal monomer units. Chain-growth condensation polymerization for the synthesis of aromatic polyamides has been applied to the construction of well-defined block copolymers and star-shaped polymers. Nickel-catalyzed condensation polymerization of 5-metalated 2-halothiophene has been found to proceed in a chain-growth polymerization manner. Detailed investigations revealed that this polymerization is a catalyst-transfer condensation polymerization, in which the chain-growth nature is attributable to intramolecular catalyst transfer. Phase-transfer polymerization in a solid-solution biphasic system, in which the monomers are stored in an unpolymerizable solid phase, has been applied to the chain-growth condensation polymerization of potassium 4-bromomethyl-2octyloxybenzoate.

The historical development of research on the living polymerization process in polycondensation is reviewed. Classical polycondensation is a step-growth process, but a living polymerization polycondensation must proceed by a chain-growth rather than a step growth mechanism. Early work demonstrated that some polycondensations do not obey Flory's statistical treatment: for example, high molecular weight polymer may be obtained, even at low conversion. This means that a chain-growth mechanism must be involved, with or without a step-growth mechanism. Recent years have seen dramatic development in understanding of polycondensations that proceed only by chain-growth (chain-growth polycondensation). Several possible mechanisms are: (1) activation of the polymer end group by changed substituent effects between the monomer and the polymer, as with aromatic polyamides, polyesters, polyethers, poly(ether sulfone)s and poly(ether ketone)s; (2) activation of the polymer end group by transfer to it of the catalyst, as with polythiophenes; (3) transfer of the reactive species, derived from the initiator, to the polymer end group, as with polymethylenes and polyphosphazenes; and (4) phase-transfer polymerization in a biphase composed of a monomer storage phase and a polymerization phase, as with aliphatic polyesters. These chain-growth polycondensations have been applied to the synthesis of condensation polymers with various architectures: block copolymers, star polymers, graft copolymers, etc. (c) 2006 Elsevier Ltd, All rights reserved.

In this review article, polycondensation that proceeds in a chain-growth polymerization manner ("chain-growth polycondensation") for well-defined condensation polymers are described. Our approach to chain-growth polycondensation is (1) activation of polymer end group by substituent effects changed between monomer and polymer and (2) phase-transfer polymerization in biphase composed of monomer store phase and polymerization phase. In the approach (1), a variety of condensation polymers such as aromatic polyamides, aromatic polyesters, aromatic polyethers, poly(ether sulfone), and polythiophene with defined molecular weights and low polydispersities were obtained. Their polycondensations had all of the characteristics of living polymerization: a linear correlation between molecular weights and monomer conversion maintaining low polydispersities, and control over molecular weights by the feed ratio of monomer to initiator. Taking advantage of the nature of living polymerization in this polycondensation, we synthesized diblock copolymers of different kinds of aromatic polyamides and of aromatic polyamide and conventional polymers such as poly(ethylene glycol), polystyrene, and poly(tetrahydrofuran), as well as triblock copolymers and star polymers containing aromatic polyamide units. Some copolymers were arranged in a supramolecular self-assembly. In the approach (2), the polycondensation of solid monomer dispersed in organic solvent with a phase transfer catalyst (PTC) was carried out, where solid monomer did not react with each other, and the monomer transferred to organic solvent with PTC reacted with an initiator and the polymer end group selectively in organic solvent, to yield well-defined polyesters.

A cyclic hexamer of 4-(methylamino)benzoic acid was crystallized from dichloromethane-ethyl acetate to give colorless prisms, which belonged to space group P1 with a = 12.441(1)Å, b = 16.003(1)Å, c = 11.7479(9)Å, α = 94.421(7)°, β = 117.911(5)°, γ = 100.205(7)°, V = 1999.5(3)Å3, and Z = 2. The compound adopted a folded conformation with all six N-methylamides having a cis (E) conformation; four intermolecular CH/n contacts were observed in the crystal. 2003 © The Japan Society for Analytical Chemistry.