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91.
Poly(vinylidene fluoride)(PVF2) produces thermoreversible gels with alkyl diesters of general formula (CH2)n (COOEt)2 as well as with camphor, a naturally occurring ketone. These gels containing polymer-solvent intercalates yield multiporous materials when subjected to controlled solvent removal techniques. The micro and meso pores are attributed to polymer-solvent complexation while the macro pores are formed as a result of removal of the solvent trapped in the fibrillar network. PVF2 –diethyl azelate (DEAZ, n = 6) and PVF2 -camphor gels produce porous polymer network when dried by cyclohexane leaching. FESEM images exhibit porous network structures with fibrillar morphology. Mercury intrusion porosimetry (MIP) shows presence of pores having diameter in the range 4 nm–400µm for both the systems. The BJH pore size distribution curves for both systems confirm the presence of mesoporosity. The HK pore size distribution plots indicate that micropores are also created and it also puts evidence of single molecule solvent intercalation between the PVF2 strands. The hysteresis between the extrusion and the intrusion curves indicates the presence of channel type/ink-bottle type structure in these systems.  相似文献   
92.
Concise total syntheses of naturally occurring antiviral indolosesquiterpene alkaloids, xiamycin C (2a), D (2b), E (2c) and F (2d), have been achieved via a late-stage oxidative δ-Csp3–H functionalization of an advanced pentacyclic enone intermediate 8. This strategy takes advantage of ipso-nitration of naturally occurring abietane diterpenoids to synthesize o-bromo nitroarene derivative 11. A Suzuki–Miyaura coupling of 11 with phenylboronic acid followed by Cadogan''s ring closure provided a modular approach to a carbazole ring required for a functionalized pentacyclic core of indolosesquiterpene alkaloids.

Enantioenriched enone 8 was synthesized via three key transformations: ipso-nitration of abietane diterpenoids to furnish o-bromo nitroarene 11, Suzuki coupling with phenylboronic acid, and Cadogan''s reductive ring closure to craft a carbazole ring.  相似文献   
93.
The melting of isothermally crystallized poly(vinylidene fluoride) (PVF2), produced in the intercrystalline spaces of poly(ethylene terephthalate) (PET) from its blends, showed a unique behavior: the melting temperature decreased with the increasing crystallinity of PVF2 (i.e., with increasing crystallization time) for PVF2 volume fractions of 0.64 and 0.51. The melting temperature of already crystallized PET also decreased as the PVF2 crystallization progressed and the isothermal crystallization temperature of PVF2 increased. Separate reasons were proposed to account for these behaviors. The equilibrium melting temperatures of PVF2 in the blends, measured by the Hoffman–Weeks extrapolation procedure, were used to calculate the polymer–polymer interaction parameter (χ21); only the noncrystallized portion of PET contributing to the mixed amorphous phase was considered. The χ21value (−1.75) was lower than χ12 (−0.14), calculated from the melting temperature depression of PET. However, when they were normalized to the unit volumes of the respective components, the two values were found to be the same. The crystallization rate of PVF2 decreased with an increasing volume fraction of PET in the blend. The Avrami exponent increased for the volume fraction of PVF2 (0.77) and then progressively decreased with an increasing volume fraction of PET. A gradual change in the nature of the regime transition from regime II/regime I to regime III/regime II with increasing PET concentration was observed. The value of the chain-extension factor of PVF2 significantly increased with an increase in the PET concentration in the blends. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 2215–2227, 2004  相似文献   
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