Crosslinking of Polydimethyl Siloxane Copolymers with Aromatic Dianhydrides: The Study of Thermal and Flame Retardant Properties †

Aromatic dianhydrides have been identified as potential candidates for crosslinking with biocatalytically synthesized siloxane copolymers containing a functional amino group on the isophthalate moieties. We present the synthesis, characterization, thermal and flame retardant properties of this novel class of crosslinked organo-siloxane copolymers. We also discuss the effect of the concentration of one of the crosslinkers, 1,2,4,5-benzenetetracarboxylic dianhydride (DAH), on thermal decomposition and flame retardant properties using thermogravimetric analysis (TGA) and pyrolysis combustion flow calorimetry (PCFC) studies. The char yields were improved in all the polymers crosslinked with the various aromatic dianhydrides. The heat release capacity of a polymer crosslinked with 20% DAH, compared to the pure polymer, was tremendously reduced from 190 J/gK to 100 J/gK. The decomposition kinetics from TGA showed that the crosslinked polymer is thermally more stable than the non-crosslinked polymer.     

Synthesis and Characterization of Amphiphilic PEG Based Polymers and Their Self Assembling Behavior

Sixteen amphiphilic polymers were synthesized using poly(ethylene glycols) (PEGs) of different molecular weights, viz. 1000, 1500, 2000 and 4000 as hydrophilic block and linkers namely azelaic acid, suberic acid, terephthalic acid and glycolic acid as hydrophobic block in the presence of catalyst conc. H₂SO₄ out of which four with glycolic acid as linker are new. Synthesized polymers were characterized by using ¹H-NMR, ¹³C-NMR and IR spectroscopy. Micellar sizes of the polymers were determined using Dynamic Light Scattering (DLS) technique which ranged from 32.1–262.0 nm and confirmed by Transmission Electron Microscope (TEM) analysis. Molecular weights were determined using HORIBA SZ-100 scientific and varied from 6.5?×?10² to 6.5?×?10³ Kilo Daltons(kDa) by Debye plot. Critical Micelle Concentrations (CMC) of the synthesized polymers was determined using electrical conductivity meter and it ranged from 105 to 125 milligrams per litre (mg L^?1).     

Mannuronolactone acetonide: easy access to C-3 OH and C-5 OH of mannose

The synthesis of d-mannuronolactone acetonide 1 is described from alginic acid and provides an efficient route for the manipulation at C-5 of mannose. Reduction gives a new acetonide of mannose, which, on further acetonation, gives [giving easy access to C-3 OH of mannose] together with a small amount of . Some silylated derivatives of mannuronolactone allow immediate access to the C-6 of mannose. Such intermediates are likely to be of value in the synthesis of derivatives of mannose.     

Supramolecular assemblies based on copolymers of PEG600 and functionalized aromatic diesters for drug delivery applications

A chemoenzymatic approach has been developed to synthesize poly(ethylene glycol)-based amphiphilic copolymers under mild reaction conditions that self-assemble in aqueous media to form polymeric nanomicelles in the range of 20-50 nm. The supramolecular organization of polymeric nanomicelles was studied by 1H NMR longitudinal relaxation time (T1) and light scattering techniques (static and dynamic). Interestingly, the enzyme novozyme-435 plays an important role in controlling the polymerization and distribution of polymer chains, which is critical for the formation of nanomicelles with unimodal distributions. The methodology developed is highly flexible as it allows the introduction of various functionalities in the polymeric nanomicelles. These self-organized nanomicelles are highly efficient drug delivery vehicles for hydrophobic and partially hydrophilic drugs, both transdermally and orally, as they have the ability to encapsulate guest molecules during self-organization. In vivo studies by encapsulating anti-inflammatory agents (aspirin and naproxen) in these polymeric nanomicelles and by applying topically resulted in significant reduction in inflammation. The % reduction in inflammation using polymeric nanomicelles containing aspirin and naproxen was 62 and 64%, respectively.     

Optimisation of irradiation and decay times in nuclear activation analyses

A mathematical model has been developed to describe the behaviour of the statistical error in the determination of gamma-ray peak areas in instrumental activation analysis as a function of the irradiation and decay times. This model has been used to investigate the best values of these parameters for the determination of a particular peak in a complex spectrum. It has also been used to investigate the effect of the maximum count rate on the best precision obtainable.     

2,3-Bis(phenylsulfonyl)-1,3-butadiene: Substrate for Michael Donor/Acceptors in a Novel Synthesis of Fused Cyclopentenes

The reaction of 2,3-bis(phenylsulfonyl)-1,3-butadiene with the anion of various 1-substituted dimethyl 1-pentenedioates has been investigated with the purpose of devising a tandem conjugate addition-[3 + 2]-anionic cyclization route for the synthesis of bicyclo[3.3.0]octenes. The reaction proceeds with complete stereospecificity as was evidenced by treating (E)- and (Z)-dimethyl (3-cyano-2-propenyl)propanedioate with NaH in the presence of the bis(phenylsulfonyl)diene. In both cases only a single cycloadduct was obtained with no detectable signs of the other diastereomer. The overall process involves a series of three sequential conjugate additions followed by benzenesulfinate ion ejection. The success of the method is dependent on the electrophilicity of the proximal pi-bond. When 2-((5-oxo-2,5-dihydrofuranyl)methyl)malonic acid dimethyl ester was used, a mixture of the tricyclic adduct as well as an allene was obtained. In this case, elimination of the benzenesulfinate group from the initially formed sulfone-stabilized carbanion is competitive with the intramolecular [3 + 2]-annulation process. The base-induced reaction of dimethyl 2-(methoxycarbonyl)-2-pentenedioate with the bis(phenylsulfonyl)diene was also studied. Even though the position of the acceptor moiety on the pi-bond was altered, the tandem Michael reaction sequence still occurs. The course of the reaction is dependent upon the length of the tether as well as the relative placement of the electron-withdrawing group on the olefin. Reaction with gamma-substituted beta,gamma-alkenyl derivatives leads to bicyclo[3.3.0]octenes, whereas beta-substituted beta,gamma-alkenyl reagents provide bicyclo[3.3.0]octenes derived from a novel alpha-elimination reaction.     

The photocurrent response of human cones is fast and monophasic

Background  

The precise form of the light response of human cone photoreceptors in vivo has not been established with certainty. To investigate the response shape we compare the predictions of a recent model of transduction in primate cone photoreceptors with measurements extracted from human cones using the paired-flash electroretinogram method. As a check, we also compare the predictions with previous single-cell measurements of ground squirrel cone responses.     

Influence of EDA-pi interactions in drug encapsulation using nanospheres

We have evaluated the influence of aromatic and hydrophobic interactions on the strength and selectivity of encapsulation using polymeric nanospheres.     

Synthesis of novel poly(ethylene glycol) based amphiphilic polymers

The synthesis of new amphiphilic polyesters based on poly(ethylene glycol) (PEGs) and studies on their solution properties are reported. Two novel monomers, dimethyl 5-n-butoxy isophthalate (2) and dimethyl 5-n-octoxy isophthalate (3) were synthesized. Three series of novel amphiphilic polyesters, i.e. poly(ethyleneoxy isophthalate)s (10-15), poly(ethyleneoxy n-butoxy isophthalate)s (16-21) and poly(ethyleneoxy n-octoxy isophthalate)s (22-27) have been synthesized from PEGs of different sizes and dimethyl isophthalates 1-3 via the transesterification-polycondensation using dibutyltin diacetate as a catalyst. The structures of the polyesters were established from a detailed analysis of their spectra, i.e. FTIR, ¹H-NMR (one- and two-dimensional) and ¹³C-NMR. By adjusting the ratio of hydrophobic (diesters) and hydrophilic (PEGs) segments in polymers, their main chain structures and solution properties could be changed. The viscosity molecular weights (M_v) of polymers, obtained from Mark-Houwink-Sakurada relationship having poly(ethylene terephthalate) as a model, were in the range of 4500-32,000 g/mol. Intrinsic viscosities were studied based on polymer backbone length (PEGs effect) and pendant group (diesters effect) and these were found to be dependent on molecular weights of the PEGs used.     

Zur Assoziation von Seifen

Zusammenfassung Zwei technische Nonylphenol(poly?thylenglykol)-?ther mit 42 bzw. 62 ?thylenoxideinheiten pro Molekül wurden zwischen 20 und 50 °C auf ihr Assoziationsverhalten in Wasser durch Dampfdruckosmometrie, Lichtstreuung und Ultrazentrifugation untersucht. Bei den dampfdruckosmotischen Messungen wurde erstmals der von der Theorie der geschlossenen AssoziationN M _I ⇄M _N geforderte s-f?rmige Verlauf der Konzentrationsabh?ngigkeit der reziproken scheinbaren Zahlenmittel des Molekulargewichtes gefunden. Die AssoziationszahlenN aus Lichtstreuungs- und Sedimentationsgleichgewichtsmessungen stimmen gut überein, sie nehmen mit steigender Temperatur zu. Die unseres Wissens erstmals für Seifen bestimmten Gleichgewichtskonstanten der Assoziation wurden für eine bestimmte Seife bei konstanter Temperatur als unabh?ngig von der verwendeten Me?methode (Dampfdruckosmometrie, Lichtstreuung, Sedimentationsgleichgewicht) gefunden. Assoziationszahlen und Logarithmus der Gleichgewichtskonstanten sind einander proportional. Zwischen der AssoziationsenthalpieΔH _I für die Anlagerung eines Unimeren und der entsprechenden Assoziationsentropie besteht unabh?ngig von Temperatur und ?thylenoxidgehalt der Seifen eine lineare Beziehung. Die Seifenmizellen sind mit gro?er Wahrscheinlichkeit kugelf?rmig. I. vgl. (1). Die Arbeit wurde mit Mitteln der Schweizerischen Volkswirtschaftsstiftung, Projekt Nr. 387, ausgeführt. Herrn Prof. Dr.W. Simon danken wir für die überlassung des Hitachi-Perkin-Elmer-Dampfdruckosmometers und des Prototyps, Herrn Dr.J. G. Watterson für die Computerprogramme.