Takehiro Kawauchi

Helix-sense-controlled synthesis of optically active poly(methyl methacrylate) stereocomplexes.

Optically active poly(methyl methacrylate) (PMMA) stereocomplexes were prepared through the helix-sense-controlled supramolecular inclusion of an isotactic (it) PMMA within the helical cavity of an optically active, fullerene-encapsulated syndiotactic (st) PMMA with a macromolecular helicity memory. The observed and calculated vibrational circular dichroism spectra revealed that the it-PMMA replaced the encapsulated fullerenes to fold into a double-stranded helix with the same handedness as that of the st-PMMA single helix through the formation of a topological triple-stranded helix.

Living polymerization of primary alkyl acrylates with t-butyllithium/bulky aluminum Lewis acids

Anionic polymerizations of primary alkyl acrylates such as ethyl acrylate (EA) and n-butyl acrylate (n-BuA) with tert-butyllithium (t-BuLi) in the presence of bis(2,6-di-tert-butylphenoxy)alkylaluminums were carried out in toluene. The polymerizations with t-BuLi/bis(2,6-di-tert-butylphenoxy)ethylaluminum at low temperatures gave syndiotactic-rich polymers with narrow molecular weight distribution (MWD) in high yields, while those with t-BuLi/bis(2,6-di-tert-butylphenoxy)methylaluminum gave polymers with broader MWD in lower yields. The monomer addition experiment revealed the livingness of the former polymerizations. The initial monomer concentration and polymerization temperature were found to affect the MWD and the stereoregularity of the obtained polymers.

Separation of C70 over C60 and selective extraction and resolution of higher fullerenes by syndiotactic helical poly(methyl methacrylate).

A one-handed helical polymer, syndiotactic poly(methyl methacrylate) (st-PMMA), recognizes the size and chirality of higher fullerenes through an induced-fit mechanism and can selectively extract enantiomers of the higher fullerenes, such as C(76), C(80), C(84), C(86), C(88,) C(90), C(92), C(94), and C(96). This discovery will generate a practical and valuable method for selectively extracting the elusive higher fullerenes and their enantiomers and opens the way to developing novel carbon cage materials with optical activities.

Preparation and Properties of Polybenzoxazinepoly(dimethylsiloxane-co-diphenylsiloxane) Hybrids as High Performance Polymers

Polybenzoxazine, poly(B-a), was hybridized with polysiloxanes by synchronizing two reactions; ring-opening polymerization of benzoxazine (B-a) and the sol—gel process of diethoxysilanes. As diethoxysilanes, mixtures of diethoxydimethylsilane and diethoxydiphenylsilane in various ratios were used to prepare polysiloxane copolymers, poly(dimethylsiloxane-co-diphenylsiloxane), P(DMS/DPS). The effect of diphenylsiloxane (DPS) content of polysiloxane copolymer on the optical, mechanical, and thermal properties of the hybrids was studied. The progress of the sol—gel process was confirmed by IR, 1H-NMR and size exclusion chromatography. Opaque poly(B-a)-P(DMS/DPS) hybrid films were obtained at high dimethylsiloxane (DMS) content corresponding to the phase separation. The domain size of the polysiloxane was evaluated from the scanning electron microscope. Meanwhile, transparent hybrid films were obtained at high DPS content, corresponding to the homogeneous phase as observed from the scanning electron microscope. The hybrid films revealed higher tensile strength and elongation at break than pristine poly(B-a) as a function of DPS content. Dynamic viscoelastic analyses of the hybrids at high DMS content revealed two glass transition temperatures (T g) corresponding to polysiloxane and poly(B-a) components, while one T g was observed at high DPS content. Thermogravimetric analysis of the hybrids revealed that the thermal stability of the poly(B-a)-polysiloxane hybrids was higher than pristine poly(B-a) depending on the DPS content.

Syntheses of novel benzoxazines having vinyl groups and thermal properties of the thermosets

Novel benzoxazines having vinyl groups were synthesized from phenol or bisphenol A, 3- or 4-vinylaniline and paraformaldehyde. The chemical structures of the monomers were confirmed by Fourier transform infrared and 1H-NMR analyses. The polymerization behavior of the monomers was monitored by differential scanning calorimetry. Exothermic peak of the monomers appeared in the range of 219–252 °C, due to the chain polymerization of the vinyl group and the ring-opening polymerization of benzoxazine occurring at the same temperature range. The thermal cure of the monomers afforded polybenzoxazines that have higher thermal properties than those from typical benzoxazines without vinyl groups. For example, glass transition temperature (Tg) increased for 40 to 100 °C by the introduction of vinyl groups, the highest Tg being observed at 290 °C. The 5% weight loss temperature determined by thermogravimetric analysis also increased by the introduction of vinyl groups.

Preparation and Characterization of Rigid Polyimide-Clay-Polydimethylsiloxane Hybrid

A series of polyimide (PI)-clay-polydimethylsiloxane (PDMS) hybrid films were successfully prepared by using two different reactions, a sol—gel reaction of diethoxydimethylsilane and imidization of polyamide acid (PAA) prepared from 3,3′,4,4′-biphenyltetracarboxylic dianhydride (BPDA) and p-phenylenediamine (PDA), in the presence of 2 wt% of organically modified montmorillonite. X-ray diffraction of the hybrid films indicated that the clay layers were exfoliated and dispersed into PI. Scanning electron microscopy was used to confirm the dispersion of PDMS and to measure the particle size of the PDMS. Thermogravimetric analysis, differential scanning calorimetry, viscoelastic analysis and stress— strain tests were used to evaluate the performance of the hybrid films. The addition of small amount of PDMS was found to overcome the brittle problem of PI-clay nanocomposites, and the PI-clay-PDMS hybrid showed excellent thermal and physical properties.

Preparation and properties of polymer alloys consisting of high-molecular-weight benzoxazine and bismaleimide

Novel polymer alloys were prepared by blending a high-molecular-weight benzoxazine (HMWB) and a typical bismaleimide (4,4′-bismaleimidodiphenyl methane (BMI)) followed by thermal treatment up to 240°C. It was confirmed by the infrared and differential scanning calorimetric analyses that the phenolic hydroxyl group formed by the ring-opening polymerization of HMWB reacted with the double bond of BMI, in addition to the chain polymerization of the double bond of BMI and the ring-opening polymerization of HMWB. This further cross-linking through the formation of ether linkage made the polymer alloy films much more tough and flexible than each homopolymer film. Moreover, viscoelastic analyses and thermogravimetric analyses of the polymer alloy films showed that glass transition temperature and thermal stability also increased by alloying.

Crystallization Behavior of Single Isotactic Poly(methyl methacrylate) Chains Visualized by Atomic Force Microscopy

We have, for the first time, successfully visualized the crystallization behavior of a single isolated polymer chain at the molecular level by atomic force microscopy (AFM). Previously, we found that isotactic poly(methyl methacrylate) (it-PMMA) formed two-dimensional folded chain crystals composed of double-stranded helices upon compression of its Langmuir monolayer on a water surface, and the molecular images of the crystals deposited on mica were clearly visualized by AFM (Kumaki, J.; et al. J. Am. Chem. Soc. 2005, 127, 5788). In the present study, a high-molecular-weight it-PMMA was diluted in a monolayer of an it-PMMA oligomer which cannot crystallize at the experimental temperature due to its low molecular weight. At a low surface pressure, isolated amorphous chains of the high-molecular-weight it-PMMA solubilized in the oligomer monolayer were observed. On compression, the isolated chains converted to crystals composed of a single chain, typically some small crystallites linked by an amorphous chain like a necklace. Detailed AFM observations of the crystals indicated that the crystalline nuclei preferentially formed at the ends of the chains, and the size of the nuclei was almost independent of the molecular weight of it-PMMA over a wide range. At an extremely slow compression, crystallization was promoted, resulting in crystallization of the whole chain. The crystallization behavior of a single isolated chain provides new insights in understanding the polymer crystallization process.

Synthesis and properties of polybenzoxazines containing pyridyl group

A novel benzoxazine containing pyridyl group (B-3py) was prepared from 3-aminopyridine, bisphenol A, and paraformaldehyde. Polymerization behavior of B-3py was investigated by differential scanning calorimetry (DSC). The DSC thermograms revealed that the exothermic peak due to the ring-opening polymerization of benzoxazine were shifted to lower temperature range by introducing pyridyl group because the pyridyl group served as a catalyst for the polymerization. B-3py was thermally treated up to 240°C on a glass plate, affording a brown colored transparent polybenzoxazine (PB-3py) film. The dynamic mechanical analysis of the film showed that the glass transition temperature of PB-3py was higher than that of a typical polybenzoxazine without pyridyl group (PB-a). This result is probably due to the further formation of hydrogen bonding through the pyridyl group as suggested by infrared analysis of the film. Moreover, thermogravimetric analysis revealed that 5 and 10% weight loss temperatures and char yield at 850°C of PB-3py were higher than those of PB-a. These results clearly indicate that the thermal properties of polybenzoxazine can be improved by introducing the pyridyl group in the network structure.

Monomer-selective living copolymerization of butyl acrylate and methyl methacrylate with a difunctional initiator—a facile synthesis of ABA-type triblock copolymer

Abstract A difunctional initiator was synthesized through the addition reaction of tert-butyllithium (t-BuLi) to 1,3-diisopropenylbenzene (DIB) in the presence of triethylamine (Et3N). Under optimized conditions, that is dropwise addition of a mixture of DIB and Et3N to a stirred toluene solution of t-BuLi at 50 °C at a molar ratio of DIB/Et3N/t-BuLi=1/2/2, the difunctional initiator was formed without oligomeriazation of DIB. Copolymerization of butyl acrylate (n-BuA) and methyl methacrylate (MMA) with the difunctional initiator in the presence of bis(2,6-di-tert-butylphenoxy)ethylaluminum [EtAl(ODBP)2] in toluene at low temperature proceeded in a monomer-selective manner; n-BuA is polymerized first, followed by MMA polymerization, to form an ABA-type triblock copolymer [PMMA-block-poly(n-BuA)-block-PMMA], which exhibits microphase separation.