Anionic ring-opening polymerization of silacyclobutane derivatives

Anionic polymerizations of 1,1-dimethylsilacyclobutane, 1,1-diethylsilacyclobutane and 1-methyl-1-phenylsilacyclobutane were investigated. Addition of 5 mol % of butyllithium to a solution of 1,1-dimethylsilacyclobutane in THF-hexane (1 : 1) at −48°C provided poly(1,1-dimethylsilabutane) in 99% yield. M_n and M_w/M_n of the obtained polymer were 2400 and 1.10. This polymerization proceeded with a living nature. M_n increased in proportion as the yield of polymer increased. Addition of the second fresh feed of the monomer to the reaction mixture restarted polymerization of the second monomer at the same rate as in the initial stage. Addition of styrene to the living poly(1,1-dimethylsilabutane) provided a poly(1,1-dimethylsilabutane-b-styrene) block copolymer. It was also found that a polymerization of 1,1-diethylsilacyclobutane in THF-hexane at −48°C showed a living nature. In contrast, a polymerization of 1-methyl-1-phenylsilacyclobutane in THF at −78°C did not show a living nature. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35: 3207–3216, 1997     

Tetrahydropyranyl-protected poly( p -hydroxystyrene) containing vinyl ether compound for three-component photopolymers

Poly(p-hydroxystyrene)s (PHSs) partially protected by tetrahydropyranyl (THP), PPT-x, containing 2,2′-bis(4-(2-(vinyloxy)ethoxy)phenyl)propane as a crosslinking agent were used as three-component photopolymers in combination with diphenyliodonium 9,10-dimethoxyanthracene-2-sulfonate (DIAS) as a photoacid generator. The PPT-x with a higher THP-protecting ratio was deprotected at higher temperatures than the PPT-x with a lower THP-protecting ratio. The conversions of vinyl ether compound in the photopolymer films were not related to the THP-protecting ratios in PPT-x and increased with increasing baking time. Under different THP-protecting ratios and prebaking temperatures, the PPT-x showed varying lithographic behavior between a positive-working mode and a negative-working mode. These three-component photopolymer solutions of PPT-x have good preservation stability. © 1998 John Wiley & Sons, Ltd.     

Novel dual-mode photoresist based on decarboxylation by photogenerated base compound

The copolymers containing a carboxyl group were used as the two-component photopolymers in combination with dimethyl 4-(o-nitrophenyl)-2,6-dimethyl-1,4-dihydro-3,5-pyridinedicarboxylate (NMHP) as a photobase generator. Under irradiation by 365 nm light, NMHP is converted to dimethyl 4-(o-nitrosophenyl)-2,6-dimethyl-3,5-pyridinedicarboxylate (NMP). NMP acts as a base catalyst for the thermal decarboxylation of a carboxyl group in the polymer. The decarboxylation in the polymer provides a negative-working photoresist under the additional flood-exposure of 365 nm light before development. This process is called the photoassisted contrast (PAC) process. NMHP acts as a dissolution inhibitor for the aqueous base development of the polymers containing a carboxyl group but NMP promotes the dissolution of the polymers. This change in the solubility inhibition of NMHP offers a positive-working photoresist without the process of post-exposure baking (PEB) and the PAC process. Therefore, NMP, the photoproduct of NMHP, produces dual-tone-mode photoresists with the copolymers containing a carboxyl group. © 1998 John Wiley & Sons, Ltd.     

Synthesis of carbosilane block copolymers by means of a living anionic polymerization of 1,1-diethylsilacyclobutane

Block polymerization of 1,1-diethylsilacyclobutane with styrene derivatives and methacrylate derivatives was investigated. Sequential addition of styrene to a living poly(1,1-diethylsilabutane), which was prepared from phenyllithium and 1,1-diethylsilacyclobutane in THF–hexane at −48°C, gave poly(1,1-diethylsilabutane)-b-polystyrene. Similarly, addition of 4-(tert-butyldimethylsiloxy)styrene to the living poly(1,1-diethylsilabutane) provided poly(1,1-diethylsilabutane)-b-poly(4-(tert-butyldimethylsiloxy)styrene). Poly(1,1-diethylsilabutane)-b-poly(methyl methacrylate) was obtained by treatment of living poly(1,1-diethylsilabutane) with 1,1-diphenylethylene followed by an addition of methyl methacrylate. Poly(1,1-diethylsilabutane)-b-poly(2-(tert-butyldimethylsiloxy)ethyl methacrylate) was also synthesized by adding 2-(tert-butyldimethylsiloxy)ethyl methacrylate to the living poly(1,1-diethylsilabutane) which was end-capped with 1,1-diphenylethylene in the presence of lithium chloride. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 2699–2706, 1998     

Novel Thermo‐Responsive Formation of a Hydrogel by Stereo‐Complexation between PLLA‐PEG‐PLLA and PDLA‐PEG‐PDLA Block Copolymers

Gel formation was discovered in an aqueous mixture of enantiomeric triblock copolymers, PLLA‐PEG‐PLLA and PDLA‐PEG‐PDLA. This system is characteristic in that an interesting sol–gel transition was induced by the stereo‐complexation of the PLLA and PDLA segments of the block copolymers around 37°C. The process of gel formation was clearly monitored by the rheological change, and the responsibility of the stereo‐complex formation for the gelation was confirmed by wide‐angle X‐ray scattering. The mechanism of this gel formation is discussed in relation to its potential applications.     

Electrooptics of β-FeOOH Particles in Aqueous Media: 1. Reversing-Pulse Electric Birefringence in the Low Field Region

Reversing-pulse electric birefringence (RPEB) of a nearly monodisperse iron(III) hydroxide oxide sample in the β-form (β-FeOOH) was measured at 25°C and at a wavelength of 633 nm in aqueous media in the presence of NaCl. The concentrations of β-FeOOH and added NaCl varied between 0.00111 and 0.0555 g/L and 0.03 and 2.0 mM, respectively. Except for the suspensions with high salt concentrations, each RPEB signal showed a dip or minimum in the reverse process upon electric field reversal, together with a smooth rise in the buildup and a fall in the decay process. The observed signals were analyzed with a new RPEB theory, which takes into account not only the permanent electric dipole moment (μ) but also the root-mean-square ionic dipole moment (m^21/2) due to the ion fluctuation in ion atmosphere, in addition to the field-induced electronic (covalent) dipole moment Δα′ E. The results showed that the slowly fluctuating moment of m^21/2 is by far the most predominant one for the field orientation of the β-FeOOH particle, though the permanent dipole moment μ may not be completely excluded. The rotational relaxation time of the whole particle was evaluated from the decay signal, while the relaxation time for fluctuating ions was estimated from RPEB signal fitting. The sign of the steady-state birefringence for β-FeOOH suspensions was positive without exception under the present conditions. The birefringence signals in the steady state (δ/d) were proportional to the second power of the applied field strength (E) in the low field region; thus, the Kerr law was verified to hold for β-FeOOH suspensions. The specific Kerr constant was evaluated for each suspension by extrapolating the values of δ/d to zero field (E→0).     

Highly selective mono-functionalization of open-cage silsesquioxane toward film-formable homopolymer

Open-cage silsesquioxanes have lower crystallinity without diminishing the thermal stability than traditional closed-cage silsesquioxanes. Two of the three siloxane groups of commercially available corner-opened cage silsesquioxanes were selectively substituted, and the remaining one was functionalized for the mono-methacrylate monomer. The resultant polymer formed a homogeneous and transparent film with high-thermal stability.     

Photo‐alignment material with azobenzene‐functionalized polymer linked in film

Application of a new azo‐polymer as a photo‐alignment material for liquid crystals (LCs) was demonstrated. 4‐(Vinyloxyethyloxy)azobenzene (VAZO), which has thermally reactive vinyl ether groups, reacted with the ? OH groups of poly(4‐hydroxystyrene) (PHS) during the baking process. The azo‐attached polymer (PHS‐VAZO) film showed anisotropic spectra after exposure to 365‐nm linear polarized light (LPL) unlike the VAZO‐doped poly(methylmethacrylate) (PMMA) film. The anisotropy of the film was small at high concentration of the azo‐chromophore because of thermal randomization of the polarized state. In the evaluation of photo‐alignment of the LC, the LC hybrid cell using the PHS‐VAZO film achieved high LC alignment. The azo‐attached polymer using the thermal reaction of vinyl ethers is useful for a photo‐alignment material. Copyright © 2002 John Wiley & Sons, Ltd.     

Elastic/adhesive double-layered PLA-PEG multiblock copolymer membranes for postoperative adhesion prevention

Tissue adhesions cause severe and life-threatening conditions, including pain, infertility, and heart defects. The purpose of this study is to develop an anti-adhesion membrane that sticks onto the injured tissues or organs in order to avoid the suturing of the membrane which may lead to the unnecessary tissue adhesion. We previously developed poly(lactic acid)-poly(ethylene glycol) (PLA-PEG) multiblock copolymers as soft, water absorbable, and quickly degradable biomaterials. The copolymer with the highest PEG content adsorbs body fluid in vivo and sticks to the tissues. In the present study thin film and nanofiber mat were prepared from the copolymer and evaluated in vitro and in vivo. The hydrophilicity and the degradation rate increased with the increased PEG content of the multiblock copolymers. The copolymer with PEG content of 88% (LE(m)-88) was quickly swollen, become viscous, and rapidly collapsed in PBS, which was suitable feature for adhesion prevention material without suturing. Various double layered membranes with different characteristics were evaluated in vivo by applying onto the cecum scrubbed with abrasive paper, and onto the heart surface after pericardium removal. LE(m)-88 was swollen with tissue fluid and had a hydrogel-like nature. LE(m)-88 film/LE(m)-32 film double layered membrane was found to be the most effective in preventing tissue adhesion in cecum model. This excellent performance was confirmed in the rat heart adhesion model. In both models, the LE(m)-32 support film was detached from the site of application, which leads to the healing without adhesion.     

Comparison theorems for oscillation of second-order half-linear differential equations

Summary We establish new comparison theorems on the oscillation of solutions of a class of perturbed half-linear differential equations. These improve the work of Elbert and Schneider [6] in which connections are found between half-linear differential equations and linear differential equations. Our comparison theorems are not of Sturm type or Hille--Wintner type which are very famous. We can apply the main results in combination with Sturm's or Hille--Wintner's comparison theorem to a half-linear differential equation of the general form (|x'|^α-1x')' + a(t) |x|^α-1x = 0.