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Introduction The reaction of isocyanates with alcohols has been widely studied and successfully used as the basic reaction during polyurethane synthesis [ 1 – 7 ]. There are several factors such as the reactant

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The urethane forming cure reactions of hydroxyl terminated polybutadiene (HTPB) binder with three different isocyanate curatives, viz., toluene diisocyanate (TDI), isophorone diisocyanate (IPDI) and 4,4'-methylene bis(cyclohexyl isocyanate) (MCHI), were investigated by differential scanning calorimetry (DSC). The effect of two cure catalysts, viz., dibutyl tin dilaurate (DBTDL) and ferrric tris-acetylacetonate (FeAA) on the cure reactions was also studied. Cure kinetics was evaluated using the multiple heating rate Ozawa method. The reactivities of the three isocyanates and catalytic efficiencies were compared based on the DSC reaction temperatures, activation energies and rate constants. Viscosity build-up in these systems at isothermal temperature was also studied and compared with the results from DSC.

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For the enhancement of thermal stability of poly(p-dioxanone) (PPDO), the isocyanate end-capping reagent was prepared by treatment of toluene-2,4-diisocyanate with an equivalent of 1-hexyl alcohol. The end-capping reagent and the end-capping PPDO with an inherent viscosity of 0.26 dL g−1 were characterized by FTIR and 1H-NMR. Thermal stability of the end-capping PPDO with an inherent viscosity of 0.92 dL g−1 was investigated isothermally and non-isothermally under air atmosphere using thermogravimetry. It has been shown that the addition of the prepared isocyanate can enhance significantly the thermal stability of PPDO. The activation energies for non-isothermal degradation estimated by Kissinger method and Friedman method are 91, 81 kJ mol−1 for as-prepared PPDO, and 160, 149 kJ mol−1 for the end-capping PPDO, respectively. The activation energy increases by about 70 kJ mol−1 through the end-capping.

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Kinetics of polyurethane formation between several polyols and isocyanates with dibutyltin dilaurate (DBTDL) as the curing catalyst, were studied in the bulk state by differential scanning calorimetry (DSC) using an improved method of interpretation. The molar enthalpy of urethane formation from secondary hydroxyl groups and aliphatic isocyanates is 723 kJ mol-1 and for aromatic isocyanates it is 552 kJ mol-1 . In the case of a single second order reaction for aliphatic isocyanates reaction, activation energy is 705 kJ mol-1 with oxypropylated polyols and 503 kJ mol-1 with Castor oil. For aromatic isocyanates and oxypropylated polyols the activation energy is higher around 77 kJ mol-1 . In the case of two parallel reactions (situation for IPDI and TDI 2-4) best fits are observed considering two different activation energies.

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Abstract  

New polyurethanes with mesogenic units in the main chain due to the use of a liquid crystalline chain extender were synthesized from 4,4'-methylenebis(cyclohexyl isocyanate) (HMDI)using diisocyanates of different trans, trans isomer content, a low molecular diol4,4'-bis(6-hydroxyhexoxy)biphenyl (BHHBP) and a high molecular poly(hexyleneadipate)diol (PHA). The growth of trans, trans isomer content in HMDI used to syntheses of PU induces monotonic growth of melting point, rectilinear growth of crystallization temperatures and the growth of crystallization enthalpy, both for hard segment polyurethanes and block polyurethanes. The increase of trans, trans isomer content in HMDI increases also glass transition temperatures and dynamic storage modulus of the polyurethanes.

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In order to investigate the utility of selected thiols as scavengers of MIC, we first assessed the chemical stability of SMG, AMCC and SMC by measuring their rates of reaction in vitro with thiophan. The inital rates of carbamoylation of thiorphan (0.5 mM) by the above conjugates (0.5 mM) in aqueous buffer at pH 7.4 and 37°C were 2.51, 0.76 and 8.47 mol L–1 min–1, respectively, indicating that the mercapturate AMCC was the most stable of the three MIC conjugates.In light of these results, studies were conducted to examine the effect of pretreatment withN-acetyl-l-cysteine (l-NAC; 500 mg kg–1, i.p.) on the urinary elimination of AMCC in rats dosed with MIC (15 mg kg–1, i.p.). In separate experiments, groups of rats were pretreated with eitherN-acetyl-d-cysteine (d-NAC) orN-trideuteroacetyl-l-cysteine (d3-l-NAC) in order to explore the mechanism by which MIC undergoes conjugation to AMCCin vivo. The results indicated that exogenous NAC effectively enhances the urinary excretion of MIC in the form of AMCC, and that it does so largely by direct conjugation with the isocyanate, rather thanvia biosynthesis to GSH.

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Non-isothermal crystallization kinetics of polypropylene (PP), m-isopropenyl-α,α-dimethyl-benzyl isocyanate grafted PP (PP-g-m-TMI), and styrene(St), as comonomer, together with m-TMI grafted PP (PP-g-(St-m-TMI)) was investigated by using differential scanning calorimetry (DSC) under different cooling rates. The crystallization rates of all samples increased with increasing cooling rate. The relation of the half time of crystallization (t 1/2) of the three samples, t 1/2(PP-g-(St-m-TMI)) < t 1/2(PP-g-m-TMI) < t 1/2(PP), implying the introduction of St could effectively improve the degree of grafting of m-TMI, resulting in crystallization temperature increased, and the crystallization rate was the fastest. Three methods, namely, the Avrami, the Ozawa, and the Mo, were used to describe the crystallization process of the three samples under non-isothermal conditions. The Avrami and Ozawa neglected the secondary crystallization that follows primary crystallization. The Mo method can successfully describe the overall non-isothermal crystallization process of all the samples. It has been found that the F(T)(PP-g-(St-m-TMI)) < F(T)(PP-g-m-TMI) < F(T)(PP), also meaning that the crystallization rate of PP-g-(St-m-TMI) and PP-g-m-TMI were faster than that of PP. The activation energy (ΔE) for non-isothermal crystallization of all samples was determined by using the Kissinger method. The result showed that the lower value of ΔE for crystallization obtained for PP-g-m -TMI and PP-g-(St-m-TMI) confirmed the nucleating effect of St and m-TMI on crystallization of PP.

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isocyanate prepolymer (MDI-ISO 145/8 from Elastogran, Hungary) and a polyol (Polyesther Elastoflex W5516/115 from Elastogran, Hungary). Two type of stabilizers were used (see Scheme 1 ): Scheme 1

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Abstract  

Different ACTRON calorimeters were used to investigate the alcoholysis of phenyl isocyanate and acetyl chloride, and the reaction of o-chloronitrobenzene with alkaline alcohol. An example for a scenario to break off a reaction in a hazardous situation is given.At least it will be shown, that it is possible to evaluate an interrupted reaction to get the kinetic activation parameters.

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