William H. Daly

The preparation of N-carboxyanhydrides of α-amino acids using bis(trichloromethyl) carbonate

Abstract A synthesis of the N-carboxyanhydrides (NCAs) of several α-amino acids using bis(trichloromethyl) carbonate, 1 , is reported. The triphosgene is used to supply phosgene in situ in stoichiometric amounts; it is particularly effective for preparing NCAs of amino acids with long, aliphatic side chains.

Quaternization of N-aryl chitosan derivatives: synthesis, characterization, and antibacterial activity.

Chemical modification of chitosan by introducing quaternary ammonium moieties into the polymer backbone renders excellent antimicrobial activity to the adducts. In the present study, we have synthesized 17 derivatives of chitosan consisting of a variety of N-aryl substituents bearing either electron-donating or electron-withdrawing groups. Selective N-arylation of chitosan was performed via Schiff bases formed by the reaction between the 2-amino groups of the glucosamine residue of chitosan with aromatic aldehydes under acidic conditions, followed by reduction of the Schiff base intermediates with sodium cyanoborohydride. Each of the derivatives was further quaternized using N-(3-chloro-2-hydroxypropyl)trimethylammonium chloride (Quat-188) as the quaternizing agent that reacted with either the primary amino or hydroxyl groups of the glucosamine residue of chitosan. The resulting quaternized materials were water soluble at neutral pH. Minimum inhibitory concentration (MIC) antimicrobial studies of these materials were carried out on Escherichia coli (Gram-negative) and Staphylococcus aureus (Gram-positive) bacteria in order to explore the impact of the extent of N-substitution (ES) on their biological activities. At ES less than 10%, the presence of the hydrophobic substituent, such as benzyl and thiophenylmethyl, yielded derivatives with lower MIC values than chitosan Quat-188. Derivatives with higher ES exhibited reduced antibacterial activity due to low quaternary ammonium moiety content. At the same degree of quaternization, all quaternized N-aryl chitosan derivatives bearing either electron-donating or electron-withdrawing substituents did not contribute antibacterial activity relative to chitosan Quat-188. Neither the functional group nor its orientation impacted the MIC values significantly.

Recent developments in cellulose grafting chemistry utilizing Barton ester intermediates and nitroxide mediation

Esters or carbonates of N-hydroxypyridine-2-thione (Barton esters) were appended to either carboxymethyl or hydroxypropyl cellulose. Irradiation of the cellulose bound Barton esters in monomer initiated free radical graft copolymerization with minimal concomitant homopolymerization. Grafting of styrene to carboxymethyl cellulose was accompanied by backbone cleavage. The hydroxypropyl spacer group minimized backbone degradation; styrene, acylamide and N-isopropyl acrylamide could be grafted to hydroxypropyl cellulose in tetrahydrofuran solution. Treatment of Barton carbonate modified hydroxypropyl cellulose with styrene in the presence of TEMPO afforded corresponding TEMPO adducts, which can be used to promote the controlled radical graft polymerization of styrene. Grafts were analyzed independently after hydrolysis of the cellulose backbone.

Synthesis and characterization of N-aryl chitosan derivatives

Selective N-arylation of chitosan was performed via a Schiff bases formed by the reaction between the 2-amino group of glucosamine residue of chitosan with an aromatic aldehyde under acidic condition followed by reduction of the Schiff base intermediate with sodium cyanoborohydride (Borch reduction). Aromatic aldehydes bearing either an electron donating or electron withdrawing substituent were used. The chemical structures and thermal properties of the N-aryl chitosans were characterized by FT-IR, (1)H NMR, (13)C NMR, TGA, and DSC. The extent of N-substitution (ES) was influenced by the molar ratio of the aldehyde to the glucosamine residue of chitosan, the reaction time and the substituent on the aromatic ring. Lower ESs resulted from N-arylation using an aldehyde with an electron donating substituent. A linear relationship between the targeted ES and the ES obtained was observed when aldehydes bearing electron withdrawing substituents were employed.

Modification of Condensation Potymers

Abstract Techniques for chloromethylation of polyarylether sulfones, poly-phenylene oxide, phenolic resin, and a model compound for the polyarylether sulfone are described. The rates of quaternization of chloromethylated polyarylether sulfone, I, and the corresponding model compound, II, with triethylamine, tri-n-butylamine, and quinuclidine in either DMSO or DMSO/dioxane are reported. Second-order kinetics are observed in the quaternization of II for the entire range of substitution. In contrast, quaternization of I followed second-order kinetics during the initial 35–60% of reaction only; higher degrees of quarternization occurred at reduced rates. After evaluating the potential impact of steric hindrance, added electrolyte, and initial extent of chloromethylation, the decrease in quaternization rate at high degrees of substitution is attributed to steric effects imposed by restricted rotation of the polymer chain. Comparable retardations are not observed during the quaternization of chloromethylated po...

Relationship between Molecular Compositions and Rheological Properties of Neat Asphalt Binder at Low and Intermediate Temperatures

The main objective of this study was to establish the relationship between asphalt binder deformation properties at intermediate and low temperatures, its molecular compositions, and mix performance. To achieve this objective, nine straight binders obtained from two asphalt suppliers were tested using the ductility and the direct tensile tests. To assess the results of these tests, selected asphalt binders were evaluated using high pressure gel permeation chromatography (HP-GPC), differential scanning calorimetry (DSC), and dynamic mechanical analysis. Measurements showed that an inverse correlation exists between binder ductility at intermediate temperatures and failure strain at low temperatures. In other words, a binder that provides high ductility at intermediate temperatures would be characterized by poor elongation properties at low temperatures. This trend was related to the binder molecular compositions as characterized by HP-GPC. An increase in the binder content of low molecular weight results in an increase in its ductility at intermediate temperatures. However, an increase in paraffinic maltene content results in the binder tending to crystallize at higher temperatures as it approaches the glassy region. This was confirmed through DSC measurements, which showed that an increase in crystalline fractions may have a negative impact on the binder stiffness at low temperatures. In general, physical properties of the binder can be strongly linked to its molecular constituents. In addition, there was a positive correlation between the binder ductility and the measured tensile strength of the mixture as well as its strain at failure. Using a binder with a high ductility resulted in a mixture with greater indirect tensile strength and a stronger ability to resist cracking at intermediate temperatures.

Interactions of aminoalkylcarbamoyl cellulose derivatives and sodium dodecyl sulfate. 2. Foam stabilization

Abstract We have compared the interactions between polyquaternium 10 and sodium dodecyl sulfate with similar complexes of mono and diquaternary ammoniumalkylcarbamoyl cellulose derivatives by measuring the foaming efficiency and foam stability of their aqueous solutions. At approximately a 1:1 stoichiometric ratio of sodium dodecyl sulfate (SDS) to quaternary groups, an insoluble precipitate began to form. Maximum foamability and foam stabilization were observed in systems close to the 2 dimensional phase boundary between soluble polymer–surfactant complexes and insoluble complexes. Foaming studies indicated that for a given amount of sodium dodecyl sulfate, the most kinetically stable foam was obtained using a monoquaternary polymer. The addition of a second cationic charge on the grafted polymer substituents apparently destabilized the foam.

New Approach to Recycling Asphalt Shingles in Hot-Mix Asphalt

AbstractThe objective of this study is to introduce a new approach to recycling asphalt shingles in asphalt paving construction in which recycled asphalt shingles (RAS) are ground to ultrafine particle sizes and blended with asphalt binder through a wet process. In the proposed wet process, the ground recycled material is blended with the binder at a high temperature prior to mixing with the aggregates. Two unmodified binders that are classified as PG 64-22 and PG 52-28 were blended with two contrasting sources of RAS at a modification content ranging from 10–40% by weight of the binder. The use of RAS modification through the proposed wet process was successful in the laboratory. Based on the results of the experimental program, the use of RAS modification through the proposed wet process would generally improve or not influence the high temperature grade of the binder, but it may reduce the low temperature grade of the binder. As demonstrated in this study, an optimum shingle content may be identified t...

Grafting of vinyl polymers to carboxylated poly(arylene ether sulfone) utilizing barton ester intermediates and nitroxide mediation

Esters of N-hydroxypyridine-2-thione (Barton esters, BE) were appended to a carboxylated poly(arylene ether sulfone), PSF-COOH, backbone. Irradiation of the polymer bound Barton ester in monomer/DMF solution initiated a free radical graft polymerization at 25°C without promoting concomitant homopolymerization. The following monomers were grafted to PSF backbones using this technique: styrene, methyl methacrylate, vinyl pyridine and acrylamide. Since the grafts are attached to the backbone by an ester linkage, the graft segments were cleaved and subjected to independent characterization. Graft length is dependent upon the [BE]/[M], and the degree of BE substitution on the backbone. Treatment of BE modified PSF with styrene in the presence of TEMPO afforded the corresponding TEMPO adducts, which were used to promote the controlled radical graft polymerization of styrene.

Synthesis and properties of fluorinated poly(ester-imide)s

A series of new, fluorinated poly(ester-imides)s has been synthesized by solution condensation, in a high-boiling-point solvent, of dihydroxy compounds containing imide and hexafluoroisopropylidene units with diacid chlorides containing preformed ester groups. Solutions of these polymers in NMP or in a mixture of trifluoroacetic acid with chloroform were cast into colourless, thin, flexible films having a low dielectric constant. These polymers show high thermal stability, with the initial decomposition temperature being over 400cC. The glass transition temperature is in the range 215-272C for fully aromatic structures and is about 170 TC for those polymers containing some ethylene groups along with aromatic ones. All these characteristics are discussed and compared with those of related poly(esterimide)s which do not contain 6F groups.