New Fluorinated Poly(imide siloxane) Random and Block Copolymers with Variation of Siloxane Loading

Several new random and block copoly(imide siloxane)s have been prepared by the solution polycondensation of commercially available 4,4′-oxydianiline (ODA) and amino-propyl terminated polydimethylsiloxane (APPS) with 4,4′-(hexafluoro-isopropylidene)diphthalic anhydride (6FDA). The siloxane loading was kept to 10, 20, 30, 40 and 50 wt% in the copolymers. The random copolymers were prepared by a one pot solution imidization technique, and two pot solution imidization technique was adopted for the synthesis of the block copolymers. The diamine ODA and the dianhydride 6FDA composed the hard block segment, while APPS and 6FDA composed the soft block segment. The hard block length was kept constant while the soft block lengths were varied by varying the siloxane loading. Accordingly, block copoly(imide siloxane)s were prepared on increasing the soft block lengths (DP) from 3 to 6, 10, 18 and 36 for fixed hard block length of 22. The resulting polymers have been well characterized by IR, NMR and GPC techniques. Thermal and mechanical properties of the random and block copolymers were compared with the already reported homopolyimide without siloxane moiety.     

Crystallization of Pseudopolymorphs of Some Gamboge Pigments. Pyridine,Dimethylformamide and Dimethylsulfoxide Solvates of Morellic Acid,Gambogic Acid and Guttiferic Acid

Abstract

Morellic acid, gambogic acid and guttiferic acid are related naturally-occurring xanthone pigments that yield X-ray quality crystals only from solvents like pyridine, dimethylformamide (dmf) and dimethyl sulfoxide (dmso). The structures of four of these crystals have been determined and are found to contain solvents of crystallization. The solvents hydrogen bond to the carboxyl groups with O—H…O/N motifs previously seen in other carboxylic acids. Distinctive, however, is the presence of an extended though somewhat diffuse array of C—H…O hydrogen bonds that aggregates the entire solute-solvent assemblage in a multi-point manner. Pyridine and dmf are able to mimic each other with respect to their hydrogen bond donating and accepting characteristics and in this respect play equivalent roles in their solvates with morellic acid and gambogic acid. Dmso is seen to self-associate in its guttiferic acid solvate. It is possible that these solvents with multiple hydrogen bonding donor and acceptor capability can act as hydrogen bond nucleators, providing just enough rigidity to the solutes to ensure crystallization.     

Fluorophore-labeled Polyamidoamine (PAMAM) Dendritic Architectures: Synthesis and Fluorescence Sensing Properties

Novel polyamidoamine (PAMAM) dendrimers (G=0.5–2.5) with a naphthalene core unit have been prepared. They were found to display acid as well as metal ion sensitive fluorescence signal amplification, making them of potential use as chemosensing materials. PAMAM dendritic wedges as well as naphthalene-centered PAMAM dendrimers were characterized by FT-IR, ¹H and ¹³C NMR spectroscopic methods and elemental analysis.     

Phase diagram study of CaBr2–CaHBr system

A study of binary, CaBr₂–CaHBr system was carried out by differential thermal analysis (DTA), covering the composition range from 100 % CaBr₂ to 100 % CaHBr between room temperature and 800 °C. From DTA results, the contour of solidus and liquidus temperatures with composition is plotted and the phase diagram of CaBr₂–CaHBr system is constructed. The system shows an eutectic reaction at 576 °C and the eutectic composition is 79.6 mol% CaBr₂. Co-existing phases in different phase fields are characterized by X-ray diffraction analysis.     

Association reaction between SiH3 and H2O2: a computational study of the reaction mechanism and kinetics

The association reaction between silyl radical (SiH₃) and H₂O₂ has been studied in detail using high-level composite ab initio CBS-QB3 and G4MP2 methods. The global hybrid meta-GGA M06 and M06-2X density functionals in conjunction with 6-311++G(d,p) basis set have also been applied. To understand the kinetics, variational transition-state theory calculation is performed on the first association step, and successive unimolecular reactions are subjected to Rice–Ramsperger–Kassel–Marcus calculations to predict the reaction rate constants and product branching ratios. The bimolecular rate constant for SiH₃–H₂O₂ association in the temperature range 250–600 K, k(T) = 6.89 × 10^?13 T ^?0.163exp(?0.22/RT) cm³ molecule^?1 s^?1 agrees well with the current literature. The OH production channel, which was experimentally found to be a minor one, is confirmed by the rate constants and branching ratios. Also, the correlation between our theoretical work and experimental literature is established. The production of SiO via secondary reactions is calculated to be one of the major reaction channels from highly stabilized adducts. The H-loss pathway, i.e., SiH₂(OH)₂ + H, is the major decomposition channel followed by secondary dissociation leading to SiO.     

Studies in [3, 3] Sigmatropic Rearrangement: Regioselective Cyclization of 5-(Cyclohex-2-Enyl)-6-Hydroxy-1-Methylquinolin-2(1H)-One

Thermal [3,3] sigmatropic rearrangement of 6-cyclohex-2-enyloxy-1-methylquinolin-2(1H)-one (3) afforded 5-cyclohex-2-enyl-6-hydroxy-l-methyl-quinolin-2(1H)-one (4) in 86% yield. Compound 4 on treatment with pyridine hydrotribromide in CH₂Cl₂ gave exclusively non-bridged product 6 (85%) whereas compound 4 by a different route viz., acetylation followed by bromine addition and cyclization gave the bicyclic product 7 (80%). Compound 4 also furnished a bicyclic product 11 (80%) on treatment with cone. H₂SO₄.     

Convenient Synthesis of Bicyclic Lactones Related to the Trichothecenes

Short and convenient synthesis of bicyclic lactones (1) and (2), important intermediates in trichothecene synthesis is described.     

Regioselective Synthesis of Thiopyrano[3,2‐c][1]benzothiopyran‐5(2H)‐one and Thieno[3,2‐c][1]benzothiopyran‐4(2H)‐one

4‐Mercaptothiocoumarin was alkylated with different propargylic and allylic halides under phase‐transfer‐catalyzed conditions in the presence of tetrabutylammonium bromide (TBAB) or benzyl triethylammonium chloride (BTEAC) catalyst in dichloromethane–aqueous NaOH solution (1%) at room temperature. These 4‐thiopropynyl and thioallyl thiocoumarins were then refluxed in chlorobenzene and quinoline to give thiopyrano[3,2‐c][1]benzothiopyran‐5(2H)‐one and thiopyrano[3,2‐c][1]benzothiopyran‐4‐one respectively.