Periodic radial growth in ring-banded spherulites of poly(epsilon-caprolactone)/poly(styrene-co-acrylonitrile) blends

The isothermal crystallization process of a PCL/SAN blend (90/10 wt.-%) was investigated by using real time image analysis and hot stage optical microscopy. It was found that the growth rate of ring-banded spherulites in the isothermal crystallization process is not constant. Slow growth occurs in the bright bands, while fast growth is found in the dark bands. The radially unequal growth rate of ring-banded spherulites in PCL/SAN blends may be related to the convex band structure on the surface. This new discovery gives us the idea that rhythmic growth is effective in the growth process of ring banded spherulites.

The formation of ring-banded spherulites of poly(epsilon-caprolactone) in its miscible mixtures with poly(styrene-co-acrylonitrile)

Ring-banded spherulites in polymer blends of poly(epsilon-caprolactone) (PCL) and poly(styrene-co-acrylonitrile) (SAN) were investigated by optical microscopy equipped with a digital image analysis system. PCL/SAN blends exhibit not only spherulites with a Maltese cross, but also distinct extinction rings. The periodic distance of rings changes with blend ratio and crystallization temperature and was plotted as a function of the undercooling and overall mobility of the mixtures, respectively. It was found that the overall mobility of chain segments in the mixtures could be mainly attributed to the origin of the formation of ring-banded spherulites. It was believed that for the first time a quantitative experimental result was obtained about the relationship of periodic distance of rings and the overall mobility of the mixtures. This relationship may be useful to explain the formation mechanism of ring-banded spherulites in polymer blends or even in homopolymers in the future. (C) 1977 Elsevier Science Ltd.

Synthesis, structure and ring-opening polymerization of macrocyclic arylates containing phthalic unit

A series of macrocyclic arylate dimers have been selectively synthesized by an interfacial polycondensation of o-phthaloyldichloride with bisphenols. A combination of GPC, FAB-MS, H-1 and C-13 NMR unambiguously confirmed the cyclic nature. Although single-crystal X-ray analysis of two such macrocycles reveals no severe strain on the cyclic structures, these macrocycles can undergo facile melt polymerization to give high molecular weight polyarylates.

Isolation, spectra, structure, and ring-opening polymerization of strained macrocyclic aryl(ether ketone) dimer

Macrocyclic arylene ether ketone dimer was isolated from a mixture of cyclic oligomers obtained by the nucleophilic substitution reaction of bisphenol A and 4,4'-difluorobenzophenone and easily polymerized to high molecular weight linear poly(ether ketone). The cyclic compound was characterized by FTIR, H-1- and C-13-NMR, and single-crystal x-ray diffraction. Analysis of the spectral and crystal structure reveals extreme distortions of he phenyl rings attached to the isopropylidene center and of the turning points of the molecular polygons. The release of the ring strain on ring-opening combined with entropical difference between the linear polymer chain and the more rigid macrocycle at temperatures of polymerization may be the proposed motivating factors in the polymerization of this precursor to high molecular weight poly(ether ketone). (C) 1997 John Wiley & Sons, Inc.

Synthesis, structure, and ring-opening polymerization of macrocyclic aromatic esters: A new route to high-performance polyarylates

A series of macrocyclic arylate dimers have been efficiently synthesized by an interfacial polycondensation of o-phthaloyl dichloride with bisphenols. A combination of GPC, FAB MS, and H-1 and C-13 NMR unambiguously confirmed the cyclic nature. Although single-crystal X-ray analysis of one such macrocycle reveals no severe strain on the cyclic structure, these macrocycles can undergo facile melt polymerization to give high molecular weight polyarylates.

H-1 nmr study on the ring opening selectivity of aromatic dianhydrides towards methanol

Several isomeric aromatic diester-diacids may appear as a result of the opening selectivity of anhydride groups towards the alcohol. H-1 n.m.r. was thus used to characterize the isomeric structure and to quantify the isomer composition. It was found that the isomer ratios quantitatively correlate with electron affinity of bridged dianhydrides and is independent of the alcohol structure used. Furthermore, the H-1 n.m.r chemical shift of bridged diester-diacids was found to be a very sensitive probe of chemical nature of bridged groups and can be used as indices of the opening selectivity. (C) 1997 Elsevier Science Ltd.

Activation of a ring methyl substituent in pentamethylcyclopentadienyl rhenium(V) compounds: Synthesis and characterization of the 1,2,3,4-tetramethyl-5,6-dihydrofulvene-5,6-dithiolato complex [ReO{(S)(SCH2)C(5)Me(4)}(C(5)Me(5))]

Reaction of the half-sandwich rhenium(v) complexes [Re-Cl-4(C(5)Me(5))] or [Re(O)Cl-2(C(5)Me(5))] with H2S in chloroform in the presence of pyridine leads to the chiral dithiolato complex [ReO((S)(SCH2)C(5)Me(4))(C(5)Me(5))] 1.

RING-OPENING POLYMERIZATION OF TETRAHYDROFURAN WITH RARE EARTH-CONTAINED CATALYSTS

Rare earth trifluoroacetates, Ln(CF3CO2)(3) (Ln = thirteen rare earth elements), combined with R(n)AlH(3-n) (R = methyl, octyl, n = 3; R = ethyl, i-Butyl, n = 2, 3) were used as catalysts for the polymerization of tetrahydrofuran (THF). The activity increased by adding propylene oxide (PO), as a promoter, to the polymerization system, producing high molecular weight polytetrahydrofuran (PTHF). The effects of Ln, PO/Ln, and Al/Ln, and others on the polymerization of THF were also studied. (C) 1993 John Wiley & Sons, Inc.

THE RING-BANDED SPHERULITE STRUCTURE OF POLY(EPSILON-CAPROLACTONE) IN ITS MISCIBLE MIXTURES WITH POLY(STYRENE-CO-ACRYLONITRILE)

The structure of the PCL spherulite in poly(epsilon-caprolactone)/poly(styrene-co-acrylonitrile) (PCL/SAN) blends was investigated by optical microscopy and small angle light scattering. The spherulite structure with a Maltese cross has been observed in pure PCL. Similar PCL/SAN blends exhibited not only spherulites with a Maltese cross, but also distinct extinction rings. The H(v) light scattering pattern especially caused diffraction rings in PCL/SAN blends but not in pure PCL. The spherical symmetry of spherulite PCL becomes more incomplete and the twist of the lamella becomes more irregular with increasing SAN content. It is found that the spherulite structure of PCL/SAN blends is dependent on the crystallization temperature and the concentration of SAN in PCL/SAN blends.

AMPEROMETRIC DETECTION AT A CARBON-FIBER ARRAY RING GLASSY-CARBON DISK ELECTRODE IN A WALL-JET CELL

A wall-jet cell incorporating a carbon fibre array ring/glassy-carbon disk electrode has been constructed, and characterized by the cyclic voltammetry and flow-injection techniques. The ring (composed of several microdisks) and glassy-carbon disk electrode, can be used separately for different purposes, e.g., detection in solution without a supporting electrolyte, collection/shielding detection with dual-electrode and voltammetric/amperometric detection with series dual-electrode. The electrode shows better collection and shielding effects than usual ring-disk electrode in quiescent solution and the series dual-electrode in a thin-layer flow-through cell. The detection limit at the ring electrode is comparable with that at a conventional-size electrode, and has been used in the mobile phase without a supporting electrolyte, proving to be a promising detector for normal-phase liquid chromatography.

DILUTE SOLUTION PROPERTIES OF RING-SHAPED POLYSTYRENE II. THE SECOND VIRIAL COEFFICIENTS

Using a low angle laser light scattering photometer (LALLS) the second virial coefficients(A_2) of ring-shaped and linear polystyrene (RPS and LPS) samples were determined in both toluene and butanone solutions. The A_2 of RPS in the good solvent (toluene) is smaller than that of LPS with the same molecular weight, but in the poor solvent (butanone) these two are very close. For RPS in the molecular weight range of 4×10~4——2.2×10~5, we haveA_(2r)=1.28×10~(-2)M_w~(-0.283) (Toluene 25℃) and A_(2r)=5.06×10~(-2...

Skeleton-rearranged pentacyclic diterpenoids possessing a cyclobutane ring from Euphorbia wallichii

Two novel rearranged trachylobane diterpenoids, designated as wallichanol A (2) and wallichanol B (3), consisting of an unprecedented pentacyclic skeleton named wallichane with a cyclobutane ring, and a new ent-trachylobane diterpenoid, 3-oxo-ent-trachyloban-17-oic acid (1), were isolated from the roots of Euphorbia wallichii. Their structures were elucidated by comprehensive analysis of 2D-NMR spectroscopic data, with the stereochemistry of 1 confirmed by X-ray crystallographic study. All of these compounds potently block osteoclastogenesis in vitro, suggesting a potential therapeutic application in prevention of osteoporosis.