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  • Author or Editor: B. Bogdanov x
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Abstract  

The soft segment crystallinity and morphology of poly(ester-urethanes) (PEUs) based on poly(&-caprolactone) (PCL) as a soft segment and an aliphatic diisocyanate in the hard segment were studied. It was found that the restriction of the crystallization of the PCL soft segment depends on the hard segment concentration, the length of the soft segment, and the total molecular mass of the PEUs. The PEU based on a low molecular mass PCL (M=2000) is an amorphous elastic material during a long time after casting from solution or after melt crystallization. A soft-hard segment endothermal mixing transition (Tmix) of about 70-80C is observed in the DSC curves of this PEU sample.

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Abstract  

The melting and crystallization of copolymers of tetrafluoroethylene with ethylene, synthesized in bulk and in suspension by semi-flow method, were studied by DSC. X-ray diffractions and infrared spectra of the copolymers were measured and new crystalline reflections different from those of the homopolymers were observed. The melting temperature of the copolymers synthesized in bulk depends strongly on the composition and exhibits several maxima. A certain small decrease in the melting temperature within the range of the alternating composition is observed. For alternating copolymers synthesized in suspension, the peaks are monomodal indicating a higher structural and chemical homogeneity of the copolymer. The nonisothermal crystallization kinetics in the temperature interval from 260 to 255°C of the alternating copolymer prepared in suspension can be described by a modified Avrami equation. The mechanism of nucleation and nuclei growth during the nonisothermal crystallization of the tetrafluoroethylene-ethylene copolymer is close to that of polyethylene.

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Abstract  

The influence of a wide range of concentrations (0.1–40 mass%) of Na(K)I on both the thermal behaviour and melt indexes of polyoxyethylene (POE) in a broad temperature interval was investigated by combined dynamic thermal analysis and with an extrusion plastometer. It was found that addition of 2–5 mass% of alkali salts resulted in the optimum thermal stability of POE and increased the melt index of high molecular POE, regardless of the mode of introduction of the additives into the polymer.

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Abstract  

Hydrogels prepared by crosslinkage of gelatin with dextran dialdehyde have been characterized by dynamic shear oscillation measurements at small strain. Isothermal as well as temperature scan measurements were performed. The results obtained demonstrated that the final polymer network is a result of a chemical gelatin-dextran dialdehyde interaction as well as a gelatin-gelatin (physical association) and a polymer-solvent interaction. This balance is strongly dependent on the composition of the system, the polymer concentration, the storage temperature and the storage time. We found that a short cryogenic treatment at −20°C of physically structured gels, significantly increases the chemical crosslinkage. DSC measurements at low cooling rate confirm these results and demonstrate a chemical reaction enthalpy contribution.

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Abstract  

The thermal behaviour (from 20 to 500°C) of high-molecular polyoxyethylene-urea mixtures which formed a molecular complex was investigated by means of a derivatograph. Under the conditions of the investigation, there were no indications of an interaction between the thermal decomposition products and the initial components, or of new intermediates with a thermostabilizing effect. A linear coorelation was obtained between the mass loss at 250°C and the urea content of the mixture, which may be used to determine the urea content of similar mixtures.

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