Yoshinobu Isono

Preparation and characterization of novel star-shaped copolymers having three different branches

Abstract Star-shaped copolymers having three different branches, poly(styrene), poly(dimethylsiloxane), and poly(tert-butyl methacrylate), were prepared by coupling of poly(styryl) anion with end-reactive poly(dimethylsiloxane), followed by anionic propagation of tert-butyl methacrylate. End-reactive poly(dimethylsiloxane) was prepared by anionic polymerization of hexamethylcyclotrisiloxane initiated with the lithium salt of p -(dimethylhydroxy)silyl- α -phenylstyrene. The resultant polymers were characterized by osmometry, g.p.c., 1 H-n.m.r., and found to be pure and to have narrow molecular weight distributions.

Preparation and characterization of natural rubber dispersed in nano-matrix

Abstract Preparation of a model nano-matrix-dispersed polymer was investigated in terms of graft-copolymerization of deproteinized natural rubber latex with styrene, using tert -butyl hydroperoxide/tetraethylenepentamine as an initiator. The products were characterized by 1 H-NMR spectroscopy and size-exclusion-chromatography after ozonolysis. The grafting efficiency of styrene was found to be more than 90% under the best condition of the graft-copolymerization. The morphology of the film specimens, prepared from graft-copolymers, was observed by transmission electron microscopy after staining the films with OsO 4 . Natural rubber particle of about 0.5 μm in diameter was dispersed in polystyrene matrix of about 15 nm in thickness.

Morphology of model three-component three-arm star-shaped copolymers

Abstract The microdomain structure of a model three-component, three-arm, star-shaped copolymer consisting of polystyrene (PS), poly(dimethylsiloxane) (PDMS) and poly(tert-butyl methacrylate) (PTBMA), each of them having nearly the same weight fraction, was investigated by means of differential scanning calorimetry (d.s.c.), transmission electron microscopy (TEM) and small-angle X-ray scattering (SAXS). D.s.c. results exhibiting the glass transition of PS and PTBMA and the crystallization and melting of PDMS strongly suggest the microphase separation of the three components into three microdomains. The microdomain structure is considered to be extremely complicated because the chemical junction points of the three constituent polymers must be confined on the lines where three kinds of interfaces meet. TEM and SAXS results strongly support the existence of a very regular microdomain structure with three-fold symmetry. Each of the three components possibly forms a three-dimensionally continuous network domain resulting in an ordered tricontinuous microdomain structure.

Stress Relaxation and Differential Dynamic Modulus of Carbon Black-Filled Styrene-Butadiene Rubber in Large Shearing Deformations

Abstract Combined measurements of shear stress relaxation and differential dynamic storage and loss shear moduli G′ and G″ have been made on styrene-butadiene rubber (type 1502) containing 50 phr N299 carbon black and 10 phr Sundex 790 oil, both cured and uncured, and compared with similar measurements on the cured and uncured gum rubber. The range of temperature was −22.5° to 63°C, and of static shear strain 0.01 to 0.40; the maximum oscillatory shear strain was about 0.005 and the frequency was usually 0.64 Hz. Dynamic measurements of G′ and G″ with no superposed static strain and stress relaxation measurements at small strains on the filled samples could be reduced by frequency-temperature superposition with αT shift factors that were somewhat larger than those that applied to the raw or crosslinked gum. At about 0.6 Hz, the filler increased the storage modulus by about a factor of 5 for the cured sample and about 10 for the uncured; the moduli for the cured and uncured filled samples were almost ident...

Effect of Gel on the Green Strength of Natural Rubber

Abstract The outstanding properties of natural rubber, e.g., green strength and rapid crystallization, were attributed to the chemical branching that formed at both chain ends of the rubber molecule during the preservation of the latex in the presence of ammonia. The gel content of natural rubbers from various clonal origins increased during the preservation, but decreased after deproteinization of the aged latex. The crystallization of acetone-extracted rubber was slightly suppressed as the gel content increased. The increase in green strength during the preservation was studied in connection with the gel content and degree of branching of the rubber.

Characterization of fatty acids linked to natural rubber-role of linked fatty acids on crystallization of the rubber

Abstract Natural rubber isolated from Hevea brasiliensis contains two types of long chain fatty acids: fatty acids linked to rubber chain at the chain-terminal and those present as a mixture. The composition and role of these fatty acids were characterized by 1 H NMR spectroscopy, gas chromatography and differential scanning calorimetry. The linked fatty acids were composed of saturated and unsaturated C 10 –C 22 fatty acids, the composition of which was similar to that of mixed fatty acids. As models of natural rubber, fatty acid groups, such as decanoyl (C 10 ), myristoyl (C 14 ) and stearoyl (C 18 ), were esterified to synthetic cis -1,4-polyisoprene (IR) selectively at 3,4 isomeric units, by hydroboration followed by esterification with acyl chloride. The acceleration effect of linked fatty acids on the crystallization behavior was analyzed for these models and natural rubber. The IR linked with myristoyl group showed the most rapid crystallization at −25°C among the samples prepared, as it was mixed with palmitic acid. This was explained to be due to the nucleating effect of saturated fatty acid and plasticizing effect of unsaturated fatty acid for the polymer.

Depolymerization and ionic conductivity of enzymatically deproteinized natural rubber having epoxy group

Abstract Preparation of liquid epoxidized natural rubber (ENR) was made by oxidative depolymerization of ENR in latex stage without loss of epoxy group. Epoxidation of fresh natural rubber latex, which was purified by deproteinization with proteolytic enzyme and surfactant, was carried out with freshly prepared peracetic acid. The glass transition temperature ( T g ) and gel content of the rubbers increased after the epoxidation, both of which were dependent upon an amount of peracetic acid. The gel content was significantly reduced by oxidative depolymerization of the rubber with (NH 4 ) 2 S 2 O 8 in the presence of propanal. The resulting liquid epoxidized rubber ( M n ≈10 4 ) was found to have well-defined terminal groups, i.e. aldehyde groups and α-β unsaturated carbonyl groups. The novel rubber was applied to transport Li + as an ionic conducting medium, that is, solid polymer electrolyte.

Fabrication of solid polymer electrolyte based on block-graft copolymer. 1. Precision synthesis and characterization of polystyrene-block-[poly(p-hydroxystyrene)-graft-poly(ethylene oxide))-block-polystyrene

Abstract Block-graft copolymer, poly(St)- block -[poly(HSt)- graft -poly(EO)]- block -poly(St) was prepared from styrene (St), p-tert -butoxystyrene (BuOSt), and ethylene oxide (EO) in four steps through anionic polymerization: (1) block copolymerization of St, BuOSt, and St; (2) deprotection of tert -butoxy group; (3) potassiation of phenolic OH; (4) graft copolymerization of EO initiated from phenoxide anion. The samples obtained were confirmed to have predictable number and length of graft chains as well as predictable length of backbone triblock copolymer and narrow molecular weight distributions by precise characterization using osmometry, 1 H and 13 C-NMR. The sample showed very clear microphase separation structure and the sample/LiCIO 4 complex showed high ionic conductivity. The block-graft copolymer is expected to be a new class of material for solid polymer electrolyte.

Stress Relaxation and Differential Dynamic Modulus of Polyisobutylene in Large Shearing Deformations

Stress relaxation in shear has been measured at 25°C for a polyisobutylene sample with viscosity average molecular weight 7.7×105, at shear strains γ from 0.2 to 0.5, over a time scale from 102 to 104.5 s. In this range, the relaxation modulus G(γ;t) could be expressed by the product G(0;t)h(γ); at γ=0.5, h=0.76. Simultaneous measurements of the differential storage and loss shear moduli, G′(ω,γ;t) and G″(ω,γ;t) were made throughout the relaxation process by intermittently superposing small oscillating deformations with a maximum additional strain of 0.01, at a frequency of about 0.33 Hz, which falls in the middle of the plateau zone of the polymer. For γ=0.2, G′ and G″ remained unchanged from their values at zero static strain, G′(ω,0) and G″(ω,0) respectively, confirming that the density of entanglements (or topological obstacles, or temporary network junctions), remains constant throughout the relaxation process at small strains. At higher strains, G″ was nearly constant, but G′ was somewhat smaller at...

Weak acid-strong base type charge-mosaic membrane. I. Carboxylic acid-quaternary amine system

Abstract A film prepared from a pentablock copolymer, poly [isoprene-b-styrene-b-isoprene-b-(4-vinylbenzyl)dimethylamine-b-isoprene] (ISIAI), was subjected to chemical modification in three steps: the A block was quaternized, the I block was cross-linked, and the S block was acylated. The threelayer lamellar structure of the original film was retained even after these processes. The resulting membrane behaved as a charge-mosaic membrane at higher pH values and as an anion-exchange membrane at lower pH values, the behavior corresponding to the degree of dissociation of the carboxyl group. This weak acid-strong base type charge-mosaic membrane exhibited quite high ion selectivity in comparison with previous strong acid-strong base type charge-mosaic membranes.