Takayuki Otsu

Controlled Synthesis of Polymers Using the Iniferter Technique: Developments in Living Radical Polymerization

In this review, we describe the concept of iniferters and the model for living radical polymerization in a homogeneous system, which was proposed in 1982 by one of the authors to enable the controlled synthesis and molecular design of polymers through the radical polymerization process. The iniferters are classified into several types: thermal or photoiniferters; mono-, di-, tetra-, or polyfunctional iniferters; monomeric, polymeric, or gel iniferters; monomer or macromonomer-iniferters, leading to the syntheses of monofunctional, telechelic, and polyfunctional polymers, block and graft copolymers, and branched, star, and cross-linked polymers. Phenylazotriphenylmethane and tetraphenylethane derivatives serve as thermal iniferters, and some organic sulfur compounds act as photoiniferters. Among the iniferters, several compounds containing N,N-diethyldithiocarbamyl groups were found to be excellent for the synthesis of polymers with well-controlled structures. The synthesis of various types of block, star, and graft polymers with a controlled chain structure through living radical polymerization using dithiocarbamate compounds as photoiniferters is described. In the last section, the recent developments in living radical polymerization using nitroxides and transition-metal complexes since 1993 up to 1997 have also been reviewed.

Kinetic study of radical polymerization of dialkyl fumarates using electron spin resonance spectroscopy

The radical polymerization of dialkyl fumarates (DRF) bearing various ester alkyl groups was kinetically studied. The propagation and termination rate constants were determined using electron spin resonance (ESR) spectroscopy. The introduction of the bulky ester alkyl groups such as a tert-butyl group decreased the termination rate constant as expected. However, it has also been revealed that the bulky groups promote propagation despite the steric repulsion. The propagation rate and mechanism are discussed in relation to the propagation manner, i.e., tacticity of the polymer.

Effect of N-substituents on polymerization reactivity of N-alkylitaconimides in radical polymerization

Abstract Radical polymerization and copolymerization of N -alkyl-substituted itaconimides were kinetically investigated in benzene at 60 °C. The rate constants of propagation and termination were determined using the ESR method during the homopolymerization. The cross-propagation rate constants were also evaluated from monomer reactivity ratios during the copolymerization with styrene or methyl methacrylate. The effects of the N -substituents on the polymerization rates, propagation rate constants, cross-propagation rate constants, and termination rate constants were discussed. The polymerization reactivity of the itaconimides was compared with those of other related monomers that had been previously reported, i.e. dialkyl itaconates, dialkyl fumarates, N -substituted maleimides, and alkyl methacrylates.

Radical polymerization of dicyclohexyl fumarate and its derivatives as studied by electron spin resonance spectroscopy

Abstract The radical polymerization of dicyclohexyl fumarate (DCHF) and its derivatives was carried out with dimethyl 2,2′-azobisisobutyrate in benzene at 60 °C. The propagation and termination rate constants (kp and kt) were determined by electron spin resonance spectroscopy. The kp and kt values were 0.48−0.91 l mol sec and 14−23,000 l mol sec , depending on the DCHF concentration ( 0.1−1.5 mol l ). It has been revealed that the alkyl substituents on the cyclohexyl ring have important effects on the polymerization reactivity of the DCHF derivatives. The 2-substituted cyclohexyl derivatives showed a lower polymerization reactivity because of the decrease in kp. The propagation manner of the 2-substituted derivatives is discussed, based on the results of the investigation of the tacticity of the polymer in comparison with those of non- or 4-substituted derivatives.

Opening and addition modes in propagation during radical polymerization of fumaric and maleic derivatives

Abstract Polymers of bis(trimethylsilyl) fumarate, di-tert-amyl fumarate, and methyl tert-amyl fumarate were prepared by radical polymerization at 60 or 120°C. The polymers were converted into poly(dimethyl fumarate) via thermolysis or hydrolysis and subsequent methylation to determine the tacticity using 13C-NMR spectroscopy. The probabilities of meso addition (P m) were revealed to be 0.66 (60°C) for the bis(trimethylsilyl) ester, 0.60 (60°C) and 0.52 (120°C) for the di-tert-amyl ester, and 0.54 (60 and 120°C) for the methyl tert-amyl ester. From the temperature dependence of the P m values, the differences in activation enthalpies and entropies for the meso and racemo additions were evaluated. The microstructure of poly(dimethyl fumarate) derived from poly(maleic anhydride) was also examined. The opening and addition modes in propagation of the fumaric and maleic derivatives were discussed based on the results obtained in the present and previous work.