Shoichiro Yano

Physical properties and structure of organic-inorganic hybrid materials produced by sol-gel process

Two approaches of the sol-gel process to prepare organic-inorganic hybrids are reviewed. One method is simple and involves mixing an organic polymer with a metal alkoxide such as tetraethoxysilane (TEOS). During the sol-gel process the inorganic mineral is deposited in the organic polymer matrix forming hydrogen bonding between organic phase and inorganic phase. In the small angle X-ray scattering (SAXS) profiles of such hybrids, the scattering intensity increases with increasing amount of inorganic mineral incorporated into the organic matrix, but no peak occurs. The dynamic modulus of such hybrids increases with increasing TEOS content and is accompanied by a decrease in tan δ peak intensity. No significant change in the position of the tan δ peak occurs, because the molecular motions of the organic polymer are not restricted by the deposited silica component. Hydrogen bonded hybrid systems of hydroxypropyl cellulose (HPC), poly(vinyl alcohol) (PVA), and poly(vinylidene fluoride) (PVDF) are described. Another method is to introduce triethoxy silyl groups into the organic polymer prior to the sol-gel reactions with TEOS. In this review two methods are described. One method involves terminating the ethoxy silanes on both ends of the organic polymer with urethane or urea linkages using isocyanatopropyltriethoxysilane. Another method is to copolymerize the organic monomer with vinyl triethoxysilane. The SAXS profiles of covalently bonded hybrids are much different than those for hydrogen bonded hybrids. A large sharp peak occurs in the SAXS curves and the peak height increases with increasing TEOS content. This is perhaps due to micro phase separation between silica-rich domains and the organic polymer matrix. The dynamic modulus increases with increasing TEOS content and the tan δ peak height decreases. The tan δ peak position shifts towards higher temperatures due to the molecular motions of the organic polymer being restricted by the silica rich domains. Highly functional hybrids derived from the sol-gel process are being developed for practical applications such as coatings, contact lenses and non-linear optical, electrochromic, and electroconductive materials.

Molecular Design of Heat Resistant Polyimides Having Excellent Processability and High Glass Transition Temperature

The relationship between the imide structures and morphology are discussed in order to develop heat resistant polyimides having excellent processability and toughness. Addition-type imide oligomers consisting of asymmetric 2,3,3′,4′-biphenyltetracarboxylic dianhydride (a-BPDA) and 3,4′-oxydianiline (3,4′-ODA) and/or 4,4′-oxydianiline (4,4′-ODA) with 4-phenylethynyl phthalic anhydride (PEPA) were synthesized and characterized. The imide oligomers derived from 3,4′-ODA; 4,4′-ODA (50:50) comonomer having molecular weights of 5240 g mol−1 (Oligo-10) and 1340 g mol−1 (Oligo-1.5) showed good solubility in aprotic solvents such as DMAc and NMP, and were successfully cured at 370°C for one hour. The thermal curing process, and thermal and rheological properties of the imide oligomers were investigated by FT-IR, differential scanning calorimetry, thermogravimetric analysis, and dynamic rheometry. It was observed that the melt flow dramatically decreased above the T g for Oligo-1.5, resulting in a viscosity as low as 200 Poise at 300°C. Whereas, a melt viscosity for Oligo-10 was 20 000 Poise at 365°C. The glass transition temperatures of these cured oligomers were 341°C and 308°C, respectively. In addition to the excellent melt property, the cured oligomers exhibited good thermo-oxidative stability. Furthermore, the cured imide oligomer consisting of a-BPDA and 4,4′-ODA with PEPA (Oligo-4.5) exhibited over 13% flexural elongation and a T g of 343°C. Their T-300 carbon fibre composites were also well consolidated demonstrating excellent processability and properties. It is concluded that amorphous, aromatic imide structures without any weak linkages such as alkyl and methylene groups are very effective in the molecular design of heat resistant, addition-type polyimides. The excellent properties exhibited in a-BPDA based polyimides demonstrate a promising potential for future aerospace applications.

Preparation and characterization of hydroxypropyl cellulose/silica micro-hybrids

Hydroxypropyl cellulose (HPC) was incorporated in situ with silica by the sol-gel process involving various amounts of added tetraethoxysilane (TEOS), and hybrids with nanometre-sized silica particles were prepared. To determine the effect of TEOS content on the mechanical properties of the micro-hybrids, the TEOS content in the hybrids was varied from 20 to 60%. The mechanical properties of the micro-hybrids were compared with those of HPC composites mixed with various amounts of glass beads (diameters of 20–40 μ m) by solvent blending. The ultimate tensile strength of the micro-hybrid was improved from 6 to 18 MPa when the TEOS content reached 40 wt%. On the other hand, the strength of the blend composite decreased with glass-bead content. The α 1 - (molecular motion in a highly ordered amorphous phase), α 2 - (molecular motion in a random amorphous phase) and β -relaxations (relating to molecular motion of hydroxypropyl groups) were observed in the temperature dependence of the dynamic viscoelastic properties of HPC. The level of the dynamic modulus, G ′, of the micro-hybrid increased with initial TEOS content. By hybridization, the α 1 -peak in the tan δ curve broadened and its intensity lowered as the initial TEOS content increased. The α 2 -peak was observed for the micro-hybrid composed of 20 wt% TEOS, but disappeared when the TEOS content exceeded 40 wt%. The β -peak was not observed in the hybrid. No drastic change was observed in the dynamic viscoelastic behaviour of the blend composite as the glass-bead content was varied. The mechanical properties of the in situ micro-hybrid were completely different from those of the blend composite. This difference was caused by the interaction between the filler and matrix. In the micro-hybrid, nanometre-sized ceramic particles may be dispersed in the HPC component, and strong interaction occurs via hydrogen bonding. In contrast, the interaction between the glass beads and HPC in the blend composite is weak.

Dynamic viscoelasticity and structural changes of regenerated cellulose during water sorption

Abstract The dynamic viscoelasticity of regenerated cellulose was studied as a function of relative humidity (r.h.). At 50 and 80°C the dyanamic modulus E′ decreased rapidly at about 70–80% r.h. and a steplike change in E′ was observed at 50–60% r.h. Simultaneously, a peak in tan δ appeared at about 90–95% r.h. and a shoulder was observed at about 50–60% r.h. From the X-ray analysis and nuclear magnetic resonance study, the steplike change in E′ and the shoulder in tan δ at about 50–60% r.h. may be caused by crystal growth accompanied by molecular rearrangement due to sorbed water. The significant drop of E′ and the tan δ peak at 90–95% r.h. may be due to the onset of micro-Brownian motion in the plasticized chain molecules.

First Catenane‐Containing Phosphino Groups: A Step toward a Catenane Ligand

Abstract A novel [2] catenane containing a diphenylphosphino group on each ring was prepared. Synthesis of the new catenane involved the use of tetraamide rings to form an efficient pseudorotaxane intermediate. The catenane was found to be applicable as a ligand for metal-catalyzed reactions such as Suzuki-Miyaura coupling.

Chemical recycling of commodity vinyl polymers: selective preparation of end-reactive oligomers by controlled thermal degradation

A newly designed experimental apparatus has been developed to effectively depress the secondary reactions of volatiles, which are the primary products of thermal degradation of polymers. In this communication, we report that controlled thermal degradation of polystyrenes and polypropylenes leads to effective preparation of novel macromonomer-like oligomers and telechelic oligomers.

Dynamic viscoelastic properties of carboxymethylcellulose during isothermal water sorption

The dynamic viscoelastic properties of carboxymethylcellulose sodium salt (NaCMC) were measured isothermally as a function of relative humidity (r.h.). The dynamic modulus decreased with increasing r.h. and dropped markedly at about 70% r.h. In the tan δ curve, a small peak appeared at about 20–30% r.h. and a large peak was observed at 80% r.h. To study the mechanism of these relaxations, the dynamic modulus was measured isothermally as a function of time at constant r.h. and the data were analysed in terms of the kinetics. Below about 70% r.h. bound water may be formed, having an activation energy of 15.0–15.6 kJ mol−1. On the other hand, above 70% r.h., two types of mechanism may occur simultaneously: formation of bound water around hydrophilic groups with activation energy of 15.6 kJ mol−1, and formation of free water with activation energy of 13.0 kJ mol−1. Consequently, the tan δ peak occurring at about 20–30% r.h. may be caused by the onset of local molecular motion of the hydrophilic groups, and the peak at about 80% r.h. by the onset of micro-Brownian motion of chain molecules plasticized with free water.

An effective method for selective formation of telechelic oligomers by controlled thermal degradation of polypropylenes

Abstract The controlled thermal degradation of some samples of isotactic and syndiotactic polypropylenes with molecular weights ranging from 3.8×10 4 to 1.1×10 5 in M n was examined to develop an effective method for selective formation of telechelic oligomers having two isopropenyl end groups, TVD. The principal conditions are at 370°C for 30–90 min. The average number of TVD per molecule f t determined from the 13 C NMR spectrum of the nonvolatile oligomers ( M n 3000–7000) isolated from the sample residues in the degradation ranged from 1.5 to 1.9 with an increase in the initial molecular weight of the original polymer, independent of the stereoregularity. The maximum f t value observed is 1.87, which indicates that about 88 mol% of the oligomer molecules are structurally symmetric telechelic oligomers having two TVDs. With an increase in the initial molecular weight M n0 , the yield of residue decreases and the relative molecular weight ( M n / M n0 ) of the nonvolatile oligomers decreases. These results strongly suggest that the intermolecular hydrogen abstraction of volatile radicals occurs more frequently than that of the terminal macroradicals, because almost all of the end double bonds of these oligomers are formed via the intermolecular hydrogen abstraction of various radicals followed by the β scission of on-chain macroradical and, thereby, the marked increase of f t value is caused by a greater contribution of volatile radicals to the scission of main chains of polymer molecules. Thus, it becomes clear from these results that the rates of elementary reactions in the degradation process increases with an increase in initial molecular weight owing to the diffusion-controlled mechanism of termination.

Temperature dependence of the tensile properties of lignin/paper composites

Abstract The mechanical properties of dioxane lignin (DL)/paper and kraft lignin (KL)/paper composites were investigated as functions of temperature and strain rate. The tensile properties of the lignin/paper composites were governed by the viscoelastic properties of lignins used as a matrix. In the temperature dependence of the tensile properties, the strength of DL/paper composite decreased at 70° and 130°C at which the elongation had maxima. This behaviour was caused by the viscoelastic properties of DL having two relaxations in the primary dispersion region at 120° and 160°C. In the case of KL/paper composite, a drastic decrease in the strength and maximum of elongation were observed at the glass transition of KL (140°C). The strain rate dependence of the strength of DL/paper composite showed behaviour typical of viscoelastic materials. The strength increased with increase of the strain rate and then decreased after reaching a maximum, which showed a transition from a brittle to a ductile type of fracture.

Photo-oxidation of nylon 6 above 300 nm

Abstract The photo-oxidative degradation of nylon 6 with light above 300 nm was investigated. The increase in the dynamic modulus (E′) and the change in the ultra-violet spectrum at 280 nm were observed on irradiation with spectrally dispersed light between 300 and 600 nm. Scission was the predominant reaction accompanying crystallisation of the broken polymer segments, as shown by the decrease in intrinsic viscosity and the development of the peaks in the X-ray diffraction pattern. E′ during the photo-oxidation above 365 nm increased linearly with time reflecting crystallisation. The activation energy was obtained as 20·0 kJ/mole according to the Arrhenius relation of the rate constant k, which was determined from the equation E′t = E′0 + kt, where E′t is E′ at time t and E′0 is that at t = 0. The effect of the photo-oxidation above 300 nm on the temperature dependence of the viscoelastic property of nylon 6 was also investigated. On irradiation, the α-relaxation at 85°C broadened, the β-relaxation at −45°C decreased in its intensity, and the γ-relaxation at −95°C was unchanged in the tan δ versus temperature curves.