Kazunobu Senoo

Structural development of natural rubber during uniaxial stretching by in situ wide angle X-ray diffraction using a synchrotron radiation

Structural development of natural rubber during uniaxial stretching was examined by an in situ wide angle X-ray diffraction measurement using a synchrotron. During stretching, the amorphous part showed little change, i.e. an amorphous halo remained clear even at 500% strain. The fraction of induced crystals was very small, though a clear crystalline pattern was observed at 400% strain. Some polymer chains were oriented and crystallized, but most of the chains were not oriented at all in spite of large deformations of the specimen. Only a small amount of polymer chains contributes to the stress and hysteresis loss during elongation.

Syndiospecific copolymerization of styrene with styrene macromonomer bearing terminal styryl group by CpTiCl3–methylaluminoxane catalyst

Abstract Copolymerization of styrene with styrene-terminated polystyrene macromonomer (SSTM) by CpTiCl 3 –methylaluminoxane (MAO) catalyst was investigated. SSTM was prepared by a reaction of living polystyrene initiated with sec -butyllithium ( s -BuLi) and p -chloromethyl styrene at −78°C. The synthesized SSTM has a high terminal functionality and a narrow molecular weight distribution. Graft copolymers of polystyrene consisted of syndiotactic main chain and atactic side chain were synthesized by CpTiCl 3 –MAO catalyst. The synthesized graft copolymer was confirmed to have highly syndiotactic sequence on the main chain.

Crystallization of stretched network chains in cross-linked natural rubber

Relatively fast kinetics of strain-induced crystallization (SIC) of cross-linked samples with various network-chain densities (ν) of natural rubber and its synthetic analog was examined by the fast time-resolved wide angle x-ray diffraction and simultaneous tensile measurements. The lateral crystallite size was almost unchanged with elapsed time, though the crystallization proceeded considerably during the period. The rate of SIC was faster for the samples having the higher ν during the first tens of seconds. While the development of SIC obviously depends on ν, progress of relative stress relaxation with time was almost independent of ν. The different dependence of the experimental results on ν was explained by assuming coexistence of stretched and relaxed network chains. During SIC at a fixed strain ratio, the intensity of crystalline reflections increased without reducing the intensity of anisotropic amorphous halo on the equator. Accordingly, rather relaxed chains that had shown the off-equatorial scat...

Synthesis of porous cross-linked polymer monoliths using 1,1,1,2-tetrafluoroethane (R134a) as the porogen

In this paper, we describe the synthesis of porous, cross-linked polymethacrylate monoliths by free radical polymerization using 1,1,1,2-tetrafluoroethane (R134a) as the porogenic solvent. Solvent separations were simple (boiling point R134a=26.5 C) and the reactions were carried out at relatively low pressures (< 20 bar). It was found that the surface area and the median pore diameter of the materials could be varied over a wide range (5–320 m 2 /g and 15 nm–5 mm, respectively) by varying the monomer concentration. By contrast, pressure had little influence on the structure of the materials due to the relatively incompressible nature of liquid R134a. # 2003 Elsevier Ltd. All rights reserved.

Syndiospecific copolymerization of styrene with styrene terminated isoprene macromonomer by CpTiCl3-methylaluminoxane catalyst

Copolymerization of styrene with styrene terminated polyisoprene macromonomer (SIPM) by CpTiCl3-methylaluminoxane (MAO) catalyst has been investigated (Cp: cyclopentadienyl). SIPM was prepared by reaction of living polyisoprene initiated with sec-butyllithium (s-BuLi) and p-chloromethylstyrene. The synthesized macromonomer has a high terminal degree of functionalization and a narrow molecular weight distribution. Graft copolymers of polystyrene-graft-polyisoprene have been synthesized with the CpTiCl3-MAO catalyst. The synthesized graft copolymer was confirmed to have a highly syndiotactic sequence on the main chain.

Synthesis of a novel syndiotactic poly(macromonomer) consisting of styrene‐terminated polyisoprene macromonomers using half‐titanocene catalysts

Homopolymerization of a stytene-terminated polyisoprene macromonomer (SIPM) by half-titanocene catalysts in conbination with methylaluminoxane (MAO) was investigated. Polymerization of the SIPM with CpTiCl 3 -MAO as the catalyst was found to proceed readily to give a high molecular weight polymer. 1 H and 13 C spectra of the poly(SIPM) after ozonolysis of the isoprene side chain revealed that poly(SIPM) is a highly syndiotactic polymer. Syndiotactic poly(SIPM) is soluble in usual solvents in spite of having highly syndiotactic sequences on its main chain and a considerable degree of polymerization.

Isospecific copolymerization of styrene and a styrene‐terminated polyisoprene macromonomer with the Ni(acac)2/MAO catalyst

The copolymerization of styrene (St) with a styrene-terminated polyisoprene macromonomer (SIPM) by a nickel(II) acetylacetonate [Ni(acac)2] catalyst in combination with methylaluminoxane (MAO) was investigated. A SIPM with a high terminal degree of functionalization and a narrow molecular weight distribution was used for the copolymerization of St. The copolymerization proceeded easily to give a high molecular weight graft copolymer. After fractionation of the resulting copolymer with methyl ethyl ketone, the insoluble part had highly isotactic polystyrene in the main chain and polyisoprene in the side chain. Lowering the MAO/Ni molar ratio and the polymerization temperature were favorable to producing isospecific active sites.

Synthesis of polyisoprene macromonomer having terminal vinyl group and copolymerization of the macromonomer with ethylene and propylene

Abstract Synthesis of polyisoprene macromonomer having terminal vinyl group and graft copolymerization of the macromonomer with ethylene and propylene was investigated. The polyisoprene macromonomer having terminal vinyl group (VIPM) was synthesized by a reaction of allyl chloride with living polyisoprene (PIP) initiated with s-butyllithium (s-BuLi) catalyst. The graft copolymers consisting of olefins and VIPM as a grafts was synthesized with classical Ziegler–Natta catalyst from the copolymerizations of the prepared VIPM with ethylene (E) and/or propylene (P).

Synthesis and Characterization of Syndiotactic Polystyrene‐Polyisoprene‐Syndiotactic Polystyrene ABA Type Triblock Copolymer

The synthesis of a model ABA type triblock copolymer, consisting of syndiotactic polystyrene (SPS) (A) and polyisoprene (PIP) (B) blocks is demonstrated. The 3,4‐vinyl carbon on the polyisoprene side chain in the SPS‐graft‐PIP was effectively lithiated with sec‐butyllithium, which was subsequently utilized for further living anionic polymerization of isoprene. Propagating polyisoprenyl anions were terminated with 1,3‐diiodopropane to make the ABA type triblock copolymer. From the 1H NMR and GPC measurements, the composition ratio of ABA block was found to be almost 1:3:1.

Synthesis and processing of porous polymers using supercritical carbon dioxide

The production of porous polymers is often solvent intensive. As environmental regulations become more stringent, there is a need to consider cleaner routes to these materials. Carbon dioxide has emerged as a clean and versatile solvent for the synthesis and processing of a range of polymers(1). CO2 is inexpensive, non-toxic, non-flammable, and easily separated from products. This review focuses upon the formation of porous polymers and polymer blends using supercritical CO2 (scCO2). The advantages of CO2 are evaluated in each case.