Akira Yanagase

New approach to block copolymerization of ethylene with polar monomers by the unique catalytic function of organolanthanide complexes

This paper describes the first examples of ABA- and AB-type block copolymerizations of a nonpolar monomer, in this case ethylene, with polar monomers, such as methyl methacrylate (MMA), ϵ-caprolactone (CL), and 2,2-dimethyltrimethylene carbonate (DTC), initiated by the unique catalytic function of rare earth metal complexes [Sm(II) and Ln(III) (Ln = Y, Sm)] as initiators. The Sm(II) species conducts the ABA-type triblock copolymerization, leading to poly(MMA-co-ethylene-co-MMA), poly(CL-co-ethylene-co-CL), or poly(DTC-co-ethylene-co-DTC) by the efficient catalysis of racemic Me2Si(C5H2-2-Me3Si-4-tBu)2Sm(THF)2 (1) or meso Me2Si(Me2SiOSiMe2)(C5H2-3-tBu)Sm(THF) (2b). The resulting block copolymers are completely insoluble in THF and CHCl3, but the homopolymers of MMA, CL, and DTC are freely soluble in these solvents. TEM profiles provide direct evidence for the block copolymerizations, where the spheric morphology of homogeneously dispersed polar polymers was observed. Ln(III) species, such as racemic Me2Si(C5H2-2-Me3Si-4-tBuMe2Si)YH (5) and Me2Si(C5H2-2-Me3Si-4-tBu)SmH (6), afford AB-type block copolymers between ethylene and MMA or CL, whose TEM images reveal the homogeneous dispersion of poly(MMA) or poly(CL) units in the polyethylene region. The ABA- and AB-type block copolymers demonstrate high break stress and high tensile modulus as compared with their corresponding blended polymers.

Mechanism of enhanced impact strength of poly(vinyl chloride) modified by acrylic graft copolymer

The mechanism of enhanced PVC impact strength of poly(vinyl chloride) modified by an acrylic graft copolymer was studied by the three-point bending test on a U-notched bar. In the mechanism, the void formation from the modifier released the constrained strain. The release suppresses the stress below the fibril strength in the material; consequently, stable deformation can develop over a large area and, thus, the impact strength of PVC modified by the acrylic graft copolymer is improved.

Effect of modifier characteristics on toughness of poly(vinyl chloride)

The effects of the mechanical properties of an acrylic graft copolymer and a silicone/acrylic composite rubber graft copolymer on the toughening of poly(vinyl chloride) (PVC) are examined. In the experiment for improvement of impact resistance of PVC, toughness of the blend polymer of a silicone/acrylic composite rubber graft copolymer is improved remarkably. The effect is attributed to the suppression of stress concentration below the fibril strength of the polymer alloy effectively by releasing the constraint of strain resulting from easy void formation at low stress.

Chain transfer polymerization of methyl methacrylate initiated by organolanthanide complexes

A novel chain transfer polymerization mediated by Cp 2 *Sm(III) species and organic acids is described. The chain transfer polymerization involves the reaction of organic acids such as thiols or ketones with an active bond between samarium(III) and the enolate in a living chain and of poly(methyl methacrylate) (PMMA). This chain transfer reaction resulted in termination of the living chain end and the regeneration of the active initiator which would consist of (C 5 Me 5 ) 2 Sm(III) and deprotonated organic acids. The chain transfer polymerization was confirmed by turnover numbers (TON). tert-Butyl thiol exhibited the chain transfer reactivity effectively to control the molecular weight of PMMA without decreasing of the polymer yield and the stereoregularity. As a result of this chain transfer polymerization, thermal and optical propertics of the PMMA obtained were improved by the control of chain end groups or by reducing a large amount of the samarium initiator.

Effect of the orientation hardening of matrix polymers on the toughness of polymer blends

The effect of orientation hardening of matrix polymers on the toughness of polymer blends was examined. Both poly(methyl methacrylate) (PMMA) and poly(vinyl chloride) (PVC), with different characteristics of orientation hardening were used as matrix polymers and a silicone/acrylic composite rubber graft copolymer was used as the modifier. The efficiency of the improvement in toughness for the blend with PMMA as the matrix polymer, as a result of the addition of the modifier, was lower than that of the blend with PVC. It was suggested that the strain for the initiation of orientation hardening of PMMA was lower than that of PVC. It was concluded that the lower efficiency of toughening for PMMA blended with modifier when compared to that of the PVC blend is caused by the development of orientation hardening at a lower plastic strain.

Research of Pseudo-Living Radical Polymerization in Specific Emulsion Polymerization.

乳化重合系でのリビング重合の可能性については, Smith-Hwartの乳化重合理論における粒子生成時のメカニズムに示唆されているが実験的な議論が少なく, わずかにMikurasovaらによる開始剤を工美したリビングラジカル乳化重合の実験例が報告されているに過ぎない. スチレンの乳化重合において, 特定の乳化剤を高濃度で用いる条件で極微量の過酸化物を使用したレドックス系開始剤によるラジカル重合を行うことにより乳化重合の初期段階ではリビング重合的に進行することを明らかとした. また, この乳化重合挙動をSmith-Ewart-Gardonの理論より解析した.